Special Observing ReportScope Comparison: Argo, the Pup & the World
The Essence of Optical Excellence "Startesting" Both Scopes Different Scopes for Different Folks A Critique of Sheer Aperture Show and Tell Always Room for Improvement The Show Goes On!
The Essence of Optical Excellence
We know the stars always shine. Within the great whirling island universes, they blend their light. Many populate great cities of suns. Others inhabit lesser townships. Even without optical aid, stars join to take on delightful shapes. Wandering among them are our closest celestial neighbors. Even a single hour following Royal Jupiter's wheeling dance telescopically, reveals a continuous parade of features. And Saturn, all icy and still, can cut the field of view with absolute splendour and crystalline clarity. Our own Moon may never be exhausted of fine detail. Each view is the combined result of feature and sunlight as it plays across Selene's high contrast surface.
Between us and these celestial wonders may be all-encompassing sunlight by day. Soft, silvery moonlight by night. Twenty miles of the earth's ocean of air. Water vapor and dust of various densities. Blocking that view may be mountains, trees, and human habitations of all sort. But unlike all of this, a truly fine telescope does not inhibit the view. A truly fine telescope betray's neither sky or eye. It gets out of the way and disappears itself. It seeks only to serve, and in so doing lets light reveal itself unedited, unabridged, unexpurgated.
A night of great transparency and stillness is a rare thing of beauty. On such a night the Moon, planets and stars can almost be plucked from the sky. Even the dimmest stars shine like diamonds against the ebony of space. While the brightest glow steady and unperturbed. On the very finest nights, all of eternity could pass while the stargazer remains engrossed in the light of a single star.
A truly fine telescope will make the most of such a night. For such a telescope adds nothing to, nor detracts from, the image of the sky it presents. Every photon takes its original place. A particular study is seen enlarged and illumined by the greater resolving power, magnification, and light gathering capacity that optics can provide. Arranged and assembled photons fall upon the retina in exact verisimilitude to their emanating source. And the eye in turn, communicates a vision of that original harmony and beauty to the mind of the perceiver.
A telescope of poor optics would waste such a sky and trip over its own tripod. Pristine drops of photonic luminesence would spray about the field of view like a miscreant water hose. Yes, you might sense the presence of such a sky - even through a poor scope - but you would not become its intimate. You would not feel the swelling of the human heart as it expands to encompass this world and others...
In making this statement about fine optics - I refer not to the type of scope in use. Nor am I speaking of a particular aperture, resolving power or magnification. I refer to quality. On a perfect night, a healthy pair of human eyes is all that is needed to get in touch with the Great Beyond. A set of low power, steadily held, field-flattened binoculars can also help achieve this same mysterious sense of engagement. Rapture in seeing the Pleiades or Praesepe, for example, is possible unaided, through small binoculars, or by coma-free finderscope of almost any aperture. What is needful are the eyes, the skies, the knowledge of where and when to look and a humble receptivity to the wonders of creation.
By increasing aperture, resolving power, and magnification, numerous additional denizens of the night sky are possible. But the mere multiplication of inches is not enough to conjure up ever more refined and rapturous views. Again it comes down to quality. Quality inches may expand the depth of detail to which the finest of skies may be experienced. But aperture has it own constraints...
"Startesting" Both Scopes
The finest sky I've personally experienced occured on Tuesday evening, the 13th day of March, 2001. On that particular evening, I was fortunate to have a very fine telescope to appreciate it with. And that telescope - a 150mm Maksutov-Cassegrain - remains with me still.
Both MCT "Argo" - and achromatic refractor ('the Pup") - are the subject of this "scope review". A review which unfolds in its own way and own time. A review that flows like a river - meandering toward a sprawling delta at the frontier of a great ocean of possibilities...
Most skies I've experienced have not been as rapturous as 13 March. Some have been as still. Others, as transparent. None, in my recollection, have ever been both as still and as transparent at once.
It's easy to quantify the clarity of the night sky. It is almost as easy to assess its stability. Any decent telescope, at higher magnifications, will show average brightness stars as false or "airy" disks. This, of course, is possible when the sky is reasonably stable. As sky stability improves past this point, such an airy disk is seen to be surrounded by one (or more) luminous rings of light. These "rings" are made up of light from the star which would ordinarily have fallen into the airy disk but, because light moves in waves, is "diffracted" away from it. Generally, the dimmer and fewer these rings the better. The thinner and more evenly illumined these rings, the better. All this says that the the optical set is especially good at organizing photons. If the airy disk of a star is well-formed, shows high contrast and the first diffraction ring (moving outward) is evenly illumined for extended periods of time - the sky is extremely steady and optics highly refined and aligned (collimated).
On such a night as March 13, 2001, I could have turned Argo on a third magnitude star and, at 180x seen a single gorgeous, perfectly round "bead of light" surrounded by two rings. One very thin, concentric, evenly illumined and positioned very close to the airy disk. And a second - after a rather large gap - exceedingly faint "echo" of the first, ghostly, and pale but wonderously constructed. Thus, Argo's optics are such that they can reveal the presence of an almost perfect sky of unparalleled stability. Those who follow such things closely would say that I was seeing the first and fourth harmonic diffraction rings characteristic of a high quality obstructed telescope...
Had I been viewing that same star though the Pup, I would have seen a similarly sized airy disk at lower magnification (say 100x). The stars disk would appear a slightly flattened "bead of light". A very dim magenta fringe would be seen surrounding it - but only on eye movement. The Pup's slightly deformed first diffraction ring would display two nodes of perceptible brightening. No other diffraction rings would be seen. One of these two nodes however, would appear bright enough to be mistaken for a very, very faint, stellar companion some 2.5 arc-seconds distant from a third magnitude primary.
This slightly aberrant view of our star - even on a superb night of seeing - is the result of a lack of critical (micrometric) adjustments in the collimation of the Pup's object glass elements, lens carriage, and focuser mechanism. Add to this, slight zonal deficiencies in the shaping of one or other lense elements and we have a scope that does not quite meet the very highest standards of quality. At best, the Pup is able to perform to the limits of a very good, but less than excellent night of seeing. A night when the sky shuttles light about and randomly brightens small segments of the diffraction ring. Thus adding some slight chaos to the view at higher magnifications.
There are those in amateur astronomy (scopists by reference) who take a great deal of patience and bring much of knowledge and experience to bear in evaluating a particular scopes optics. One favored method of scope testing is to take a scope out of focus first to one side and then another and compare the resulting afocal patterns seen at high magnification. This, of course is the famed "Suiter Startest" based on evaluating the display of the "fresnel" rings seen when afocal light interferes with itself. These bright and dark regions may be inspected by the discerning eye and a particular scopes optical quality evaluated.
As a scopist, I've tried to get a better understanding of this particular arcanum. In examining Argo for instance, I've found that inside focus, the intrafocal interference pattern shows a large, circular, bright ring of light, with a second, slightly thinner ring within that. This inner ring is of similar average surface brightness to the outer one. Between these two, no others are seen. Inside the inner bright ring, a series of very faint and fine rings may be seen. These concentrically converge toward a central point of light. Meanwhile outside the outer ring, two other faint rings are visible, the outermost dimmer than its partner. Intrafocally, the pattern is very similar, except the inner "bright" ring is perceptibly dimmer (in terms of surface brightness) than the outer. In effect, the extrafocal spread of photons is not quite as well organized as the intrafocals - but very close...
| Focused Star | Disparate Double | Extrafocal Startest | Planet Saturn | Planet Jupiter |
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Argo therefore is slightly "undercorrected". Light emanating from a star tends to favor better organization inside focus and light also tends to come to more of a point at the center of the airy disk (as opposed to its perimeter). Since no optic can ever be made absolutely perfect in this regard, slight undercorrection is preferable to overcorrection. This, plus the quality of in focus views tell me that Argo is a fine scope indeed.
Not quite so the Pup. Evaluating the 80mm achromats fresnel patterns is complicated due to the amount of chromatic aberration present. Inside focus the theme is "green". Magenta fringes the outer diffraction ring while green light sprays everywhere within this. All this green makes it very difficult to see the interstitial ring pattern. While the lack of precision collimation for the two elements, lens carriage, focuser and the sloppy support for the barlow lens, mirror diagonal, and eyepiece complicates getting a good view of the inner "bright ring".
| Focused Star | Disparate Double | Extrafocal Startest | Planet Saturn | Planet Jupiter |
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Outside focus the bright ring is green-fringed with magenta spraying about elsewhere. The same mechanical issues contribute to a less than perfectly concentric presentation here as well.
To assist in seeing the inner bright ring, I have to use colored filters. Use of a medium blue filter shows that the inner bright ring - close to focus - is less defined than in Argo. The difference between intra- and extrafocal inner ring presentation is more pronounced. Like Argo, the Pup is "undercorrected". The degree of undercorrection is more severe than in the Maksutov-Cassegrain.
Ultimately the startest method as outlined above is a bit of a sham. A particular scope's true worth is measured by its "in focus" performance. If a modestly-apertured scope (say 8 inches or less) can show 3rd magnitude stars as airy disks, it has "fair optics" - regardless of ring structure. Such a scope will do a decent job of revealing the benefits of a fair sky - one where a diffuse envelope of light surrounds a star without any special organization into "diffraction rings". If a scope's optics are such that one or more concentric diffraction rings is seen - but not necessarily of especially good definition and equal surface brightness - then it will be an adequate "starsplitter" and can reveal the joys of a good night of seeing. Should the rings be well defined, and as in the Pup, show only one or two fixed brightenings, the scope will perform to a very good night of seeing's level. Finally, if like Argo, the scope shows concentric and evenly-illumined ring structure, the wonders of a truly superb night of seeing are possible.
So in a way we've exposed a method of describing scope and sky quality at once. For you see, on a one to ten scale of sky stability - with 10 being the view enjoyed by the Hubble Space Telescope. And 1 being huge, diffusely bloated blobs of stars. Our fair scope/fair sky is a 6. A good scope/sky is a 7. A very good scope/sky is an 8. And an excellent scope/sky is a 9.
Stability of sky is not our only concern in observing. Often, a sky offering perfect in focus performance is afflicted by poor transparency. High thin clouds, humidity, and stray light, all reduce a scopes ability to reveal delicate structure, locate faint studies, and present high contrast views of moon and planets.
One way to test for sky transparency is simply to determine the magnitude of the dimmest star perceptible by eye within a well-mapped constellation. My experience has been that the very best of skies allow stars to be seen down to magnitude 6.0 and beyond. Such dim stars can be seen direct and require no special aversion of the sight (which adds about a half magnitude in reach unaided and a full magnitude telescopically).
But an even better way to determine both seeing stability and transparency is through the scope itself. On a night of poor transparency but excellent stability, a fine telescope will reveal fainter and fainter stars as magnification is increased. For instance, through Argo, on an 8/10 stability night, and under a sky limited to magnitude 4.5 stars (unaided), the 13.0 magnitude star just east of M57 can easily be held direct at 300x. Meanwhile at half that magnification (150x), I would be fortunate to hold the 12.3 magnitude star in the nearby "Challice of the Ring" asterism - almost a whole magnitude dimmer...
On nights of great transparency (6.0 unaided) and fair stability (6/10), 180x is enough to hold the 13.0 star. While on a similar night under 8/10 stability even 50x will show it. Thus, the lower the magnification needed to see a dim test star, the darker the sky and the steadier the seeing. And since optical quality is equatable to seeing stability, fine optics have always been noted to increase magnitudinal reach.
So to be clear, the dimmest star I have ever held direct through Argo at the lowest magnification was a 13.4 magnitude test star near M57 at 120x on a night where 6.0 magnitude stars could be held direct. All this equates to 8/10 seeing stability at the time. Effectively Argo added 7.4 magnitudes to what could be seen unaided at a mere .8 x per millimeter of aperture.
Meanwhile, through the 80mm Pup under similar skies and also at 120x, stars to magnitude 12.3 have been held direct in the same star field. The 80mm Pup then added 6.3 magnitudes to the unaided view at 1.5 X per millimeter of aperture.
Different Scopes for Different Folks
Though the eye alone is sufficient enough to put the sensitive observer in touch with a night sky of exceptional virtue, there remain limitations. The eye can appreciate the darkness of space. Trace out constellation patterns. Hold stars and planets as points of light and follow their motion. Unaided vision can discern vague shapes upon the Moon's surface and occasionally, with intervention of passing cloud, make out large imperfections on the Sun. But, outside Sun and Moon, the eye lacks capacity for detailed vision.
To apprehend detail, the eye needs augmentation. Binoculars and telescopes accomplish this by increasing the amount of light presented to the eye and by revealing closely-spaced detail through resolution and magnification. As every amateur astronomer knows, the amount of light presented to the eye is determined by the collecting area of the object glass or primary mirror. Magnification is achieved by increasing image scale (based on focal length) and by examining the resulting virtual image through even shorter focal length "eyepieces".
Effectively, the eyepiece allows the eye to arrive at focus very much closer to the virtual image provided by the objective. The result is a significantly larger image presented to the eye. There are limits however, as to how much magnification is possible through any given scope. Image brightness falls off with magnification. As eyepiece focal lengths shorten, a point is reached where the eye can not be brought any closer to the eyepiece's eyelens. Flaws in a scopes optics (along with randomizing factors associated with atmospheric turbulence) distort the virtual image. High magnifications reveal these modifications as "aberrations" and the eye is offended.
Meanwhile the laws of physics limit a scope's ability to resolve two closely spaced "features" within the field of view. Even as the area of a telescope's objective lens or mirror limits the intensity of the light seen through the scope, and the focal length, quality of the optics and atmospheric conditions limits how much magnification of the image is possible, the diameter of the objective determines how closely two adjacent features may be proximated before they are seen as one. This, of course, is the "resolving power" of a telescope. A power which is constrained by the diffraction of light as it propagates through unfocused portions of the field.
So aperture determines how much light is admitted to the eye and determines how closely two features may be positioned in the sky and still be resolved distinctly from one another.
Finally various telescopes have differences in archetecture. These differences are intended to optimize one behavior or characteristic over another.
For instance, telescopes of the Cassegrain type were developed to "fold" the converging light cone from the light-gathering primary mirror and send it back down the length of the tube. The goal was to shorten the length of the telecope. Thus cassegrains are optimized for maximum aperture to minimum scope length. In so optimizing, the Cassegrain scope (and its various derivatives Schmidt-Cassegrain, Maksutov-Cassegrain etc.), end up including a central "plug" which blocks some of the incoming light. This plug is, in fact, a mirror that sends the light cone back down the telescope assembly through a hole in the primary to form the virtual image.
The result of such an obstruction (the "plug") is to slightly reduce the collecting area of the scope but more significantly, to diffract light away from the body of one feature to another, neighboring feature. As a result, some loss of contrast is seen between two neighboring points at the limits of resolution. Scopes of comparable optical quality - without such an obstruction - are able to show two neighboring features with a slightly greater degree of definition.
However, unobstructed scopes have their own limitations. Cassegrains evolved to keep scope lengths to a minimum while maximizing aperture. Thus inch for inch, obstructed scopes are more portable, and if fixed in installation, may be housed in smaller observatories. Cassegrains may also be designed with greater focal lengths. This improves image scale (at the expense of image intensity). Fewer optical elements may be used along the optical train, greater "eye relief" is possible (so the eye may be held further from the eyelens of the eyepiece).
Generally, scopes without an obstruction are of the refractor type. This type uses a series of lenses to collect and shape light to form the light cone. Unfortunately, refracted light does not create a single light cone naturally. This requires a great deal of care in construction, assembly, and use of exotic materials. Effectively, all scopes of the refractor type create a multiplicity of light cones based on the frequency (or color) of the light they bring to focus. Because of the resources that must go into creating a reasonably color-corrected (apochromatic) refractor, such scopes are often five to ten times more expensive than comparable obstructed scopes of equal aperture.
To be sure there are versions of refractors available that do not use exotic glasses to correct chromatic aberration. Refractor's may be purchased that use very long focal ratios (F15 plus). Due to such ratio's, these scopes are better able to bring light cones of various colors (red, green, violet) together in a way that the eye is less offended. (As focal length increases depth of field (or focus) is enhanced for all colors. Thus, a single point of focus, that includes all colors, is more easily found during focusing.) Obviously, such scopes are very large and for this reason apertures are kept small wherever portability is an issue.
A third class of inexpensive, unobstructed refractor is available. These are short focal length "rich field" achromats intended for low power use only. Such scopes are generally limited to less than one magnification per millimeter of aperture (an "exit pupil" of 1mm) so that converging light cones are not examined too closely and therefore do not offend the eye with their multitude of conflicting colored images. When using such scopes, typically the eye will see a magenta "haze" around most bright objects inside focus and a green haze outside focus. But such chromaticism is generally only seen while observing Moon, planets and bright stars. Since such scopes are used primarily for "sweeping the sky" at low power, chromaticism is not an issue.
Of course, I have already introduced you to 150mm Argo - a Maksutov-Cassegrain or MCT - and the Pup - a fast refractor of the achromatic variety. The fact that I have two scopes suggests that neither one is capable of fully meeting all my observing needs.
A Critique of Sheer Aperture
In observing the night sky, all amateurs are aware that there are limits imposed by aperture. Theoretically, increased aperture has many benefits in terms of light grasp and detail resolution. But the realities of observing through our earth's atmosphere, difficulties with creating and aligning large, well-shaped optical components, and the need to get as much of the sky as possible into the telescopic field of view all suggest that visual quality falls off as aperture increases.
So there be tradeoffs...
For instance, small scopes are more easily pressed to service. A 400mm focal length, three inch diameter rich field achromatic refractor on altazimuth mount will be used with far greater frequency than a 24 inch dobson mounted newtonian. Small scopes give larger fields of view. Our 400mm focal length scope - using an eyepiece that admits light to the full 7mm of pupil size - can be used at 11x. At 11x, an eyepiece stopped to 60 degrees of apparent field, can pull some 5 angular degrees of sky into the retina at one time. Meanwhile, our 24 inch scope must bear a magnification of 87x to ensure that all the light collected by the 24 inch primary fits through that same 7mm eye pupil. Because of this, only 41 arc minutes or roughly 2/3rds of one degree of sky can be seen fully illuminated in most common eyepieces.
Happily, with few exceptions, all single studies in the night sky are less than 41 arc-minutes. But there are other complications. As more and more of the retina receives an image, flaws in the eye (astigmatisms) may become problematic. In my own case, below 10x per inch aperture, bright stars no longer appear perfect points. In fact they flare astigmatically while passing through focus. Thus for me to see perfect stars through a 24 inch scope, some 288x is needed. This reduces the field of view to 12.5 arc-minutes!
Another tradeoff with aperture is the fact that a certain minimum exit pupil is needed to show stars against a "dark" background sky. My experience has been that roughly .5x per millimeter of aperture is the minimum magnification needed to experience this under average skies (where stars can be seen unaided down to magnitude 5.0 direct). Thus, our 24 inch scope must be used either under the darkest or at 300x plus under average skies to get a sense of skydark in the eyepiece. Meanwhile, the Pup accomplishes this same aesthetic at a mere 40 and Argo at 70x.
Larger apertures also collect more atmospherically aberrated light and make this type aberrations more apparent in the eyepiece. Generally, the 80mm Pup is able to experience 8/10 conditions where 150mm Argo experiences 7/10 skies. Thus, a rule of thumb might be that if a 3 inch scope has 9/10 seeing once every two weeks. A 6 inch scope may have 8/10 seeing that often. On that same night a high quality 12 inch scope might get 7/10 stability. While a 24 inch scope would, at best, have 6/10 seeing. At such an aperture, 8/10 seeing - even if the optics could support it - might be experienced only once or twice a year. Is it any wonder that the world's "great telescopes" were installed in locations where only the very finest seeing conditions prevail?
It is very clear to my way of thinking why scopists, such as myself, are attracted to smaller apertures. High quality scopes in the 3 to 6 inch aperture range can be found relatively inexpensively and the kind of skies needed to enjoy them come with far greater frequency.
But, if there were such a beast, and given the kind of skies that most amateurs observe through, what is the "ideal" aperture for observing all kinds of celestial studies?
Personally, I've found that - even through the very best skies - 6 inches of aperture is a little shy of the ideal. In particular, more aperture is needed to properly view face on and elliptical galaxies with satisfaction. Because of angle of presentation such galaxies provide poor contrast against the night sky. Although it is true that many of the brighter Messier-class galaxies display central starlike points and bright core regions, the frontiers of such "football-shaped" galaxies are poorly defined at six inch aperture. Also, due to innate faintness, spiral arms are rarely seen near galaxies presenting face on.
There is one class of galaxies that do give engaging and satisfying views. These are the brighter edge on galaxies. Edge-on's often offer good contrast to the night sky. A sense of "closure" is possible. Rarely do they simply "bleed off into space" - like ellipticals. Such galaxies are well-defined and show true frontiers. Unfortunately, too few edge-on galaxies of sufficient size exist to give much in the way of satisfaction. Frankly 150mm, is not enough aperture to make fine appreciation of galaxies a specialty.
Much less 80mms.
But for many other studies, and in their aggregate, six inches of aperture offers a very satisfactory deepsky experience of the heavens. In the realms of clusters and planetary nebulae, little is wanting. Add to this truly fine and well-collimated optics and numerous double stars of matched and disparate magnitudes come within reach. Include the Moon and planets Mars, Jupiter, and Saturn, and it is easy to find yourself setting up a six inch scope under numerous decent nights of seeing throughout the year.
Even the finest scopes of 80mm aperture only begin to whet the apetite for visual deepsky observation. To be sure, certain "showcase" studies give wonderful views. Many fine double stars of the 6th magnitude and brighter can be found. Numerous open clusters - and a few globulars - can be resolved. Due to limited light grasp and insufficient magnification most small planetary nebulae are out of bounds. But 80mms is just shy of the minimum needed to truly enjoy Mars and Jupiter. Ah, but Moon and Saturn can be wonderful in such a scope.
There is one area however, where a deepsky 80mm is valued - this lies in the realm of large open clusters, a few nearby galaxies, and certain over large, bright and obscuration nebulae. For here it is essential to get the "wide field" perspective - To gather as much of the night sky in the field of view as possible. And as we have seen, larger apertures and expecially longer focal length scopes are disadvantaged when it comes to studies of this kind...
It is in this area that the 80mm Pup is without peer, while 150mm Argo must go wanting. For neither perfect collimation, nor absolute color correction is needed to enjoy the Pleiades, Beehive, The Two Great Nebulae nor The Cygnus Veil Complex.
If 80mms and 150mms are shy of providing decent views of all denizens of the night sky, what aperture might be?
Setting aside the special issues of rich field telescopy, this question is fairly easy to answer (for me anyway). In attending various star parties under a variety of conditions, I've found that 200mm's of aperture provides the additional light grasp needed to enjoy every class of celestial studies. There are no exceptions here. Face on galaxies and extended bright nebulosity are all susceptible to a quality 200mm scope.
But unfortunately, few 200mm scopes possess the optical quality needed to give the kinds of views that 150mm Argo gives of Moon, planets and disparate double stars. (These are doubles whose magnitudinal delta is 1.5 or greater and are found are at or near Dawes limit of resolution.) But such scopes do exist (or can be made possible by simply collimating the optical train to the highest degree of perfection possible).
Having looked through many scopes, I've learned something else very important about deepsky observation. Even though 200mm's of aperture is ideal for all classes of studies, the difference between 200mm and 150mm - even 250 and 150 is not enough to justify acquiring a larger scope in this aperture range. However, if somehow, magically Argo's 150mm were doubled to 300mm a whole new world of observation would open up. But rare is the 300mm scope that possesses the kind of optics that can really deliver the goods. And rare is the night sky when 300mm of aperture can be put to full advantage on Moon and planets.
So 150mm is not ideal, but it is close enough...
Show and Tell
Over the last year or so, I've had a number of opportunities to observe various near and deepsky studies through both Argo and the Pup. There have also even been a few occasions when both scopes were setup side by side for comparison views. I've also had opportunities to compare the views of both Argo and the Pup with other scopes at star parties. It makes sense to gather a few of these together for convenience. The goal here is not to wax ecstatic about the virtues of either scope. No, the idea is to get a sense of what is possible using scopes of this aperture vis a vis other size (and type) amateur equipment.
What follows are all extracts from various observing reports. Most are posted right here at astro.geekjoy and can be explored in more detail by clicking on the associated link. Others are drawn from topics found on AstroTalk - the venue I now use to share information with a small community of other amateurs throughout the Blue Planet.
NOTE: AstroTalk is a members forum hosted right here on astro.geekjoy. Membership is subject to only one restriction - you need to request a password by registering.
Argo, the Pup and the Moon:
(From AstroTalk: Crater Clavius)
The Pup gave its finest view of Selene at 120X while Argo gave an equally fine view (in terms of sharpness) at twice that (240x). Both scopes showed brightenings in Plato (2) and most interestingly both brightenings at about the same level of contrast. So image scale - when searching for these ltlle "wisps" of light on the black floor of the crater - is very much an issue. (Under the 7/10 seeing - with Selene high overhead- I'm sure Argo would have showed it's usual retinue of 4 or 5 brightenings had I dropped down to the Pup's 120x magnification...)
Through Argo, also dawdled on the Alpine Valley. That region was crisply presented with many small sand-paperlike peaks marking the frontier and several fine features encroaching into and within the stilletto-like vale itself. A view sumptuous with low level detail...
But it was Clavius that really caught my eye. Here's what Menzel had to say about it in "A Field Guide to the Stars and Planets":
Quote:...largest of the lunar craters covers an area about equal to (the states of) Massachusetts and New Hampshire combined. This crater, 140 miles across, is ringed by mountains to 12,000 feet, with occasional peaks to 17,000...
Now it is not the size of the crater so much that impressed me, nor was it the mountainous rim. What impressed me was the "cochlea of craters" found within the floor of this huge basin itself. Six craters sweeping north and east from Rutherford - each smaller than the next - until impinging on the main craters southeast wall.
For you see the sweet little Pup was just able to hold the last of these at 120x - while Argo showed them all in exquisite detail and then some. For between the last of these six craters and heading back toward the originating Rutherford were a group of a half-dozen even smaller true craters that 150mm Argo revealed tantalizingly to my questing eye.
On return inside to reseach this region in Menzel's Guide, was astonished to see that Argo's powers of resolution even exceeded that of the photographic plate used as the guides moonmap - despite Clavius lying about the same distance (within two days) of the terminator.
The Pup, 70mm Ranger, and Vlacq Region:
(From SCAC Star Party -11/18/01: The Little 'Uns Square Off)
We turned both scopes on the Lunar crescent at about 70x. The limb trembled for lack of sky position. A hugely concave terminator divided Mare Crisium. A large, contrast-endowed "frozen wave" broke in a crescent shaped swath between the seas western frontier and terminator. Within that, a second dark wave broke closer to the terminator. And between these two, a faint subtle crescent shaped rise caught the lunar sunshine. There was nothing in the scene that neither scope couldn't share.
We traced the terminator south looking for "on the edge" details. A group of three larger craters (joined by a more junior fourth member) formed a parallelogram. (The largest of the four is believed to be Crater Vlacq.) Dan caught a very faint, luminous prominence almost on the point of visual extinction through the 70mm. I could not locate it - only a larger, more obvious "apostrophe" of light in that general location. Dan could make out the apostrophe too, but was unable to see the same prominence using the Pup. Score another point for the Ranger.
The lunar limb showed a faintly perceptible "magenta" glow in the 70mm. In the Pup, chomaticism was more obvious at F5 than the 70mm at F6. By installing the 67mm aperture stop, color correction became more evenly matched between the two scopes. Still, to my eye, the Ranger was very close to apochromatic. Dan expressed some pleasantries concerning the degree of color correction in the much less expensive 80mm. He also felt the two were of a kind when the Pup was stopped down to F6.
The Pup and Mars:
(From Me, the Pup and the Sky
)
Time to head for the workout deck. Mars takes center stage. First look - and even at 133X without a filter, I see a thumblike darkening to the northwest. Doesn't seem right for Mare Serpentis. Too large. Too far north. Didn't plan on doing a drawing - but the Pup's showing more than expected. Even at 20 arc-seconds, Mars is small at 133x - but the limb is pretty sharp and contrast is fine. (250X doesn't cut it though.) OK. Grab that pencil - it's sketch time! Thread in the green filter. Polar cap just not happening. Large brightening to the northeast. Another smaller brightening on the eastern limb. Red filter really brings out the northwestern mare.
Mars' low sky position allows me to remove the mirrored diagonal and view the planet direct - just like refractors of old... Not sure if this improves image quality much, but after a while, I start to make out a second darkening south-southwest. By 12:30 the viewing session is over. A sketch is ready for scanning and the Pup is stowed in the study. Run MarsPreviewerII software. Woh, so THAT was Syrtis Major: THE SYRTIS MAJOR. Meanwhile, exiting southeast was Mare Erythraeum and company. Things be happening with Mars. Now for one good night of steady seeing!
Argo and Mars:
(From The REAL THING!
)
Syrtis Major is back! Sure, local disturbances continue to obscure S. Minor and environs - but S. Major is large and in charge. At north - rimming the pole: Mare Boreum, Uchronia, & Utopia - best views yet!. Why? Because these regions contrasted nicely with a luminous North Polar Cap (NPC). Yes, the NPC (and SPC) are prominent. So for the record: This sketch was done exclusively at 180x. Medium blue and red filters employed. (Syrtis Major was visible direct). Local sky stability at or slightly better than 5/10 -(edge focus achievable).
Argo, the Pup and Jupiter:
(From Galaxies in the Mist
)
One of the deepest, most profoundly engaging mysteries of my so-called astronomical life has been the failure of the Pup to show more than the two equatorial belts on Jupiter. Well tonight I have one less mystery to confound, vex, and otherwise complicate my convoluted world. The Pup finally showed enough detail on Jupiter to slake my designs and aspirations...
Tonight's sky was comparable in stability to that of the previous evening. On that occasion, Argo gave most satisfactory views of Jupiter - irrespective of its relatively low sky position. Saturn too was well-presented. Again, despite even poorer sky position. With the prospect of good seeing before me, I couldn't help but carry both scopes out on the back lawn for a few comparisons.
Again this evening, Argo delivered views comparable to (perhaps just a tad less satisfying than) those seen last evening. Possessed of this baseline sanity check, the Pup had no choice but to deliver the goods. And with his back (hackles raised) against the wall, the Pup rose in solemn strength and did so. To wit: Belt edge irregularities on the NEB, a glimpse of the NTB, and nicely graduated polar darkening, with some macro level contrast variations in both equatorial belts. Not much, but decent for 80mm's with 11 pieces of glass between seer and seen.
What the Pup did not show: Split in the SEB, smattering of finer detail in the NEB, delicate EB, and belt-like delineation at the fringes of the polar regions.
Conclusion: If the Pup approximated Argo's aperture, views of the planets would be comparable - and possibly superior - to those revealed by Argo.
What made this comparo possible? Well of course, the fine stability. Plus the fact that I could stack two barlows together along with the 15mm Ultrascopic eyepiece to achieve a high enough magnification (150X plus).
Argo and Jupiter:
(From SCAC Bonny Dune Star Party -11/18/01: Argo's Excellent Adventure)
It was Jupiter that offered up the truly "slack jawed" view of the evening. Both the NEB and SEB went beyond the usual belt edge irregularities usually seen. On this night, under 8+/10 stability, and despite high water trapped in thin cirrus clouds well overhead, both equatorial belts showed internal structure of such complexity that I would have despaired at even attempting any kind of sketch. Now mind you, none of this intrabelt detail was "obvious". We are not talking Hubble Space telescope view here! We are talking persistent, and directly viewable variations in contrast and luminosity. Features of a type that could be counted (if I had so chosen) - if not accurately labelled.
The drawing at left was done roughly two weeks earlier than the date of this discussion. It is added as an example of what is seen of Jupiter through Argo under very good to excellent seeing conditions...
Meanwhile, between the two belts, the gossamer thin EB stretched across the width of the EZ. (Curiously however, less of the "white curdling texture" usually seen under steady seeing was present.) North of the NEB the NTB traced a very slim, but high contrast dark line across the planets considerable 210x girth. (Again curiously, 210x was preferable to 360x on this particular occasion - perhaps due to atmospheric water.) Beyond the NTB, the NTTB held a sharp line while its northern frontier blended into the NPR.
South of the rifted SEB, three belts were seen. Both the STB and STTB stood alone and isolated - darkish lines across the planets disk. While a third belt blended into the SPR just as the NTTB had done within the planets northern hemisphere.
All eight belts (this enumeration includes the two polar region conjunct belts but not the SEBn and SEBs rifted "belts") showed variations in texture (and sometimes thickness) across their lengths - even as the SEB and NEB had shown intrabelt features in their midst. Truly an extraordinary view of the planet and one that was only approximated by that seen from Fremont Peak during the Millenium change...
The Pup and Jupiter:
(From AstroTalk: Jupiter in Gemini)
Woke early this morning and decided to take a look at the Gas Giants through the reworked 80mm Pup achromat. Had the best view of both planets yet. The Pup delivered views of both planets comparable to what is seen through 150mm Argo under 5/10 seeing stability.
Although the NEB showed much greater contrast than the SEB - both EB's were easy. For the first time saw hints of barges along the NEB. Central rift suggested in the SEB. Both the NPR and SPR were definitive. Just south of the NPR could make out the NNTB. Strangely the NTB was not visible.
The planet's presentation now highly favors the NEB.
All four galileans hinted at varying sized airy disks.
Like I said best view at 80mm ever seen.
What really blew me a way was the view at 43mm. Stunning! Aperture stopped Pup is completely free of chromaticism at F9. Planets edge was crystal sharp and snapped to focus. If anything the SEB was more obvious at 43mm than at 80. However, the loss of resolution meant the disappearence of the barges on the NEB.
The Pup and Saturn:
(From AstroTalk: Saturn Still in Taurus)
Basically the view of Saturn seen was comparable to 150mm Argo under 5/10 seeing conditions. Cassini definite - but blurry. Nor could it be traced entirely around the system. SEB also obvious. Shadow of planet on posterior ring nicely visible. Good clean distinction between globe, space and ring.
The aesthetics were really quite good - but that's about all I got - good aesthetics.
For the Pup to really arrive need a sharper view of Cassini and more of Ring A to be really satisfactory...
Titan was visible - but then it was dawn. Even with the ailing Pup saw four satellites while at Crater Lake last week...
Not sure what the seeing conditions were. Didn't have a chance to check any stars before the Sun blanched the sky. But if conditions continued from last evening - probably 7/10.
Argo and Saturn:
(From AstroTalk: Saturn - On the Edge)
Last Saturday night attended a star party at the Santa Cruz Astronomy Club's Bonny Dune observing site. By 2am the sky had gotten superbly stable and transparent. Saturn had yet to reach the skies middle third but was giving simply audacious views through 150mm Argo at 120 and later 180X. The ring system is incredibly well presented. Certainly the tilt is such that the minor axis extends as far as the planets own 18 arc-second disk.
Saturn's globe was tack sharp. The southwestern edge was rimmed with sumptious shadowing. The South Equatorial Belt (SEB) pronounced - though lacking in fine detail. What I consider to be the most engaging aspect of the planet's body itself was supremely evident: Beginning slightly south of the SEB there is a blue gray mottling that extends alll the way to the south pole. The mottling is intricate in pattern and beyond all description. It is simply a texture - like a finely knit rug or carpet. The blue gray coloration most subtle and engaging.
As mentioned, the ring system itself was gloriously aspected. Cassini was sharp - but only occasionally razorlike. Outside Cassini (in Ring A) I was astonished to see the Encke Minima. (But only under the moments of finest seeing.) Why was I astonished? Because I was only viewing the planet at 180x!
Turned my attention to the transition region inside Ring B. Got a very substantial sense of a "milk-chocolate" region inside Ring B's frontier. Thus, to my eye, the Crepe Ring (Ring C) was also susceptible.
Because I was also doing a great deal of "Deep Sky" at the time, elected not to install the barlow and run up the magnification.
Other Scopes: Saturn (and Mars):
(From SCAC Star Party - 11/18/01: Planet and Stargazing Through Various Scopes)
The amazing thing about Mars is the fact that the "Incredible Shrinking Planet" is still hanging around in the night sky. And not only "hanging" but "hanging high". The planet took up a position some thirty plus degrees above the south southwestern horizon - well higher than the thin crescent Moon Dan and I had turned the little 'uns on earlier in the evening. With the planet at less than eight arc seconds apparent size, we stacked up all the magnification we could get on the 200mm Meade. Despite passable edge focus, there was just nothing to be seen beyond the planet's gibbous phase presentation. This surprised me - but only a little. Earlier I had viewed the planet at 150x through the 80mm and seen obvious darkening along the central meridian. But I'd seen this phenomenon on many other occasions and like always ascribed it to "contrast effect".
Saturn however, was another matter. The Ringed Wonder actually lay lower to the east than Mars to the west. But its 20 arc second disk and broad ring system showed quite a bit of detail. At 400x all you need do was spend a few "quality minutes" at the eyepiece and during the time you could literally follow the improvement in the planets presentation (as it gained altitude and seeing improved accordingly). Cassini's Division was evident from the beginning. Later on, as the planet approached the Zenith, we also make out the Encke Minima and hints of the Crepe Ring. On the planets disk, the broad patch of yellow which is Saturn's Equatorial Zone (EZ) surmounted by South Equatorial Belt (SEB) was a given. The SEB itself blended nicely into the temperate and this to the south polar region. The attractive "blue gray mottling" texture was visible throughout this transition.
But the 8 inch did not give the best view of Saturn seen that evening. One attendee had brought along an Orion Apex 127mm MCT. The MCT was definitely "in the zone". Its 300X view of Saturn (and later Jupiter) was superior to that of the 200mm in every respect. (Dwight and I both agreed the SCT needed collimation. Traversal of focus showed visible coma - even at magnification. Such ill-organized photonage is the bane of planetary observation.)
The Pup and Various Double Stars:
(From AstroTalk: STF 333/Eps Aries 5.2/5.6 1.4@209)
Epsilon Aries (along with Mu and Pi) were included in a report from astro.geekjoy. Of course those observations were through 150mm Argo and Epsilon was an "easy resolve". See( Two out of Three ain't Bad.)
So tonight, grabbed the Pup and made a few preliminary observations while Aries progressed toward the skies middle third.
Under 4.4 ULM and at 75x was able to "hairline separate" Epsilon-2 Lyrae. (More disparate Epsilon-1, though obviously a double, was a no show at this low a magnification.) Under same conditions, found I could just hold the 11.6 mag star in the M57 deepfield (again at 75x).
The new collimation mechanism held true from last night, and so did the stability: "8/10". Could even resolve the greenish secondary of Delta Cygni as a very faint and small "airy disk" - but only at 120x. (150 and it was too dim while at 75x lost in the primary.)
No run on Pi (Aquilae). By the time I got outside after chores (around 9:30pm) it was on the wrong side of the house. But no matter I had it's 1 magnitude brighter "twin" Epsilon Ari to go after.
And as you might expect from an 80mm (actually stopped to 77) got a Dawesian split. Elongated rod at 120x. Vaguely pinched at the waist at 240x. "Greyish-white" secondary leads pure white primary across sky and slightly to the south.
With this result, turned the scope on the Iota Cassiopeia triple - all members present and accounted for at 120x. 12.2? mag field star required slight aversion. So yah sky was not particularly deep this evening (probably approached 12.0 at 240x) but it was steady.
Once again the Pup achieved the theoretical degree of resolution. And this with a pair of stars about 1 magnitude brighter than Pi. I will note this however. Larger airy disks (VADs actually) are easier to inspect for resolution detail than smaller ones. In fact it's a pleasure to view all the Epsilons (Lyrae, Ari) but Pi is a struggle...
Argo and Various Doubles:
(From September, 2001 Reports: The Music )
To begin with had no trouble turning up STT383. New charts received from fellow observer Cor Berrevoets removed all ambiguity as to this 7th magnitude stars location. Started by dropping in on Delta Cygni. Delta showed the typical 7/10 stability view: Airy disk of primary ejecting luminosity out to the first diffraction ring. 6.4 magnitude secondary distinct and located well away from the threat of primary flaring. Decided to jack up the magnification. At 540X, sweet gray white airy disk of the secondary could be seen well away from the primaries influence. Primarys single diffraction ring distinct from its well defined but slightly unruly airy disk. Made an eyeball estimate of the relative sizes of the two stars airy disks: Primary about half-again as large as the secondary. Conditions would be excellent for resolving disparate (7.1/8.3), tight (.8 arc-second) STT383. The star was easily found some five degrees south of Delta.
The early view was suggestive but not definitive. At the time could hold stars unaided down to about 4.0. Stability not quite as good as later. Even so it was clear that something was different about this star. Eye movement revealed a "defect" near the small 7.1 magnitude primarys airy disk. The anomaly was located to the north-northeast. 360X made this evident. 540X sometimes showed a "dim companion". But it wasn't definitive. Decided to revisit the star later in the evening.
As you might guess it never did get much darker. The Moon was huge and rising to the southeast behind the foliage. The sky darkened to about magnitude 4.4 ZULM and stayed there. Despite the stability of the sky, 540X barely showed the 13.0 star east of the Ring direct. Later, as the Moon cleared the local foliage I understood why. There was a vague haze hanging in the air...
Before resuming the evening's double star theme, dropped in on the Great Hercules Cluster. Despite limited transparency (maximum telescopic limiting magnitude of 13.0 at maximum magnification), Very fine: Hundreds of stars resolvable - but no sense of "star chaining". Sky backdrop just too bright...
Turned Argo on Gamma Coronae Borealis - another "challenge double" from AstroTalk. Very tight (.74 arc-seconds) and somewhat disparate (magnitudes 4.1 & 5.6). Brightness of the primary meant it would have a relatively large airy disk. Very unlikely that a complete resolve was in the offing. Was only hoping to see the secondary as a "bump" on the limb of the primary. And that was exactly what I saw - but in the wrong position! As I was about to write up my triumphal results checked against Cor's notes on this pair. I was seeing it to the west whereas the position angle (115 degrees) is east-southeast. Decided that trying to stand up and view a close double whizzing past the eyepiece at 540X was not a good idea. Pulled up the observing stool and decided to take my time and observe more closely. Once steady (and comfortable) easily picked out the golden partial airy disk of the secondary. Here are my notes: "Almost resolvable at 540X. Yellow white primary leads golden secondary trailing and to the south. Hourglass shaped teardrop. Secondary easily held direct.".
Next on the evenings hit parade was Beta Delphinus. Surprisingly, despite hanging in one of the most easily recognized asterism in the sky - Beta was a hard find. Moon completely dominated to the southeast. This third magnitude star needed the finderscope to turn up! The pair is extremely close (.55 arc-seconds) but both stars are fairly bright (magnitudes 3.6 and 4.6). Notes say "easier than Gamma (CRB) colors pale white and gold, secondary to north-northwest and absolutely glued to the primary at 540x.. Its clear that Argo was unable to defy the laws of physics by resolving either of these sub-Dawes limit bright pairs. But it is surprising that the sky and Argo's optics could clearly show "deformations" in the airy disk of the primary caused by significantly dimmer secondaries. This is literally "on the edge" observation...
However there are limits, and this became obvious with the next pair - Tau Cygnus (AGC13). At .78 arc-seconds separation, 150mm Argo would probably just show two sixth magnitude stars of equal magnitude as separate entities. But mitigating against resolution in Tau's case are two facts: One is that the primary is brighter than 6.0 (magnitude 3.9). And as intimated above (in Delta Cygni's case) brighter stars have larger airy disks. The second and even more significant fact, is that, at magnitude 6.7, Tau's companion is 13 times dimmer than the primary. Experience has been that stars 2 times dimmer may be seen near primaries (through 150mm Argo) approaching Dawes limit. But in Tau's case, the brightness-delta far exceeds this.
Needless to say there was nothing about Tau Cygni's airy disk that smacked of anomaly. No dim "bulb" sprouting off one edge. So Argo runs up against a hard limit. Two stars at Dawes limit, one 13 times brighter than the other is just another single star glowing in the night sky...
But this was not the case with STT383. For on revisiting the pair, all ambiguity was removed. The dim secondary's bluish gray "star-point" could be held direct. This north of and slightly trailing the pale blue white primary. Two stars distinguished by 1.2 magnitudes and separated by a span approaching Dawes limit could be cleanly resolved at the highest possible magnification (540X) on a night of superb sky stability. And thus the frontier is rolled back. The Edge is probably very near - beyond which there be dragons...
Argo, 200mm LX-200 and Zeta Cancri:
(From April, 2001 Reports: I like the Night Life, I Like to Boggle! )
The sky was so stable that two of the scopes present (Argo being one) achieved clean splits of the .9 (actually .83) arc-second Zeta Cancri pair. High magnifications (roughly 350X) were required by both scopes (the other was Dwight's 8" Meade LX200). A lot of ducks have to line up on a pond to split a sub one arc-second double. First you need aperture (125mm +). And not only aperture but well-shaped optics. And not only refined optics, but good optical collimation. Then there's the right binary (equal magnitudes in the range of magnitude 4 to 8). And finally - most unpredictably - the right night. (I had not been able to conclusively split this pair earlier under 7/10 seeing.) Like I said - a lot of ducks...
The Pup, 70mm Ranger and Ring Nebula:
(From )
By this time the sky was quite dark. Large gaps of sky opened up at various times overhead. Stars to magnitude 5.0 could be held direct. Turned both scopes on M57. Again those 10 extra millimeters of aperture were a boon. Both scopes could show the 11.6 magnitude star in the Challice of the Ring. But the Pup turned up the 12.3 mag star direct, the 12.8 on moderate aversion, and the 13.0 on eye movement. The Ranger was outgunned here. Meanwhile, the Ring itself was more visibly present at 80mm's than 70. (Although both scopes showed the annular nature of the ring plus well-defined frontier.)
So as you might suspect, excellent optics of lesser aperture can't beat good optics of greater aperture at the light gathering game - even if higher quality optics does a slightly better job of organizing what light it collects...
Argo, (Other Scopes) and The Ring Nebula:
(From SCAC Star Party Potpouri)
Had one final personal study for the evening - M57 - The Ring Nebula. Like the Dumbbell, decided the Ring needed a "formalized treatment". Had absolutely no trouble turning up the King of Rings. It is an inexhaustible fount of insights, challenges, teachings, and observations. The Ring continues to engage me despite dozens and dozens of visits over the last year or so. Along with M31, M42, and M13, the Ring is the only other deepsky study I remember viewing as an eleven year old with the 4 inch Dynascope available to me at the time...
Ring Nebula drawing done May 24, 2001. It is not "scientifically correct" but is included here to give a reasonably accurate impression of how the Ring appears through Argo under a halfway decent sky. Note: It does not show the two 13 plus magnitude stars occasionally seen embedded in the flanks of the annularity. (Sorry, no central star either!) However, the "Chalice of the Ring" asterism can be seen as a large left-facing "Y" to the right of the planetary.
The Ring Nebula lies in a rich non-Milky Way field between Beta and Gamma Lyrae. Gamma is easily picked out in finderscope as the brighter of a pair of stars which align with the planetary. The Ring is not visible in the 7X35mm finder. I just set the crosshairs halfway between Gamma's finderscope companion and Beta. Then sweep around until I make out the annularity (typically, but not necessarily, at 52x). The Ring lies in an unusal region. Southwest is a "cocktail glass" asterism whose cup faces more or less directly toward the western ansae of the ring. I've given this group a personal appellation: "The Chalice of the Ring". It is comprised of about six tenth to twelth magnitude stars. East of the ring are no bright stars. A 13th magnitude star lies very close to the eastern ansae. On a better night 150mm Argo allows me to just hold this star at 180x. On the best nights, it can be held direct at 120X and an even dimmer 13.4 magnitude star well away from the ring can be seen to the north-northeast. (Last evening's star party was held under such a night.) Between these two thirteenth magnitude stars is one of magnitude 14.1. The three make excellent test studies for atmospheric tranmsparency as has been discussed earlier in this report.
The Ring itself is clearly annular and appears to be about 2x1 arc-minute in apparent size. The major axis orients roughly east-west. Its central "void" is about half this in size. It is a rare (and poor) night when the Ring's annularity can not be made out. On such occasions the void "smears" into a poorly defined ellipticity requiring averted vision to make out the darker center. Needless to say contrast must be pretty bad for this to happen.
When contrast is very good, and the sky is especially transparent, an effect similar to that seen with the Dumbbell planetary occurs. Two stars can be seen scintillating within the flanks of the Ring north and south. Happily, this was, in fact, the case last night. This effect became apparent using the 15mm 120X eyepiece - a magnification which could easily hold the 13th magnitude star just east of the Ring's major axis.
The Ring itself is not a true "ring". It is actually quite elongated and gives the sense of "a single eye opened wide in surprise". It's color, like many planetaries, is "robbins-egg blue-green". Last night, I took especial care to notice which flank of the Ring is brighter. To my eye, the northwest flank appeared slightly brighter than the southeast. Also took note of the ansae: Eastern ansae is brighter than the west - which almost appears truncated in appearance. So there's a vague sense of an insect cacoon about the Ring - but not very obvious...
At very high magnifications, the core is visibly "brighter" than dark space around it. Apparently this is one reason why the fifteenth magnitude central star is such a tough catch...
Had a look at the Ring through the 8 and 14 inch scopes. As mentioned above, both scopes shared a similar 14.1 magnitude direct threshold limiting magnitude. To be accurate, the 14 inch had a 70X eyepiece loaded, while the 8 inch had 120X on tap. But the view of the planetary itself was cleaner and crisper in both Argo and the SCT than the Dob.
Argo and Veil Complex:
(From Will the Real Veil Nebula Please Stand Out?
)
I began my exploration of this region by aligning my finder on Epsilon Cygni. I then slewed due south about 3 degrees until my crosshairs intercepted 52 Cygni. With 52 Cygni centered in the finder all I needed to do was inspect the view in the main telescope and voila -- no nebulosity. OK, so install the OIII filter, then look. Nebulosity!
52 Cygni lies just west of the Western Veil Nebula (NGC6960). At 50X, the star appears to nestle right up against it (but without actually being a part of it).
Installing an OIII filter changes the Western Veil view magically. With the filter you can see a delicately curved finger of continuously flowing luminescence about 5 arc minutes in width and 25 arc minutes long. The nebulosity winds just east of 52 Cygni then elegantly swoops down and around it to the west. The effect is that of a calmly flowing stream of diaphanous light shaped like a gull's wing in flight.
The star 52 Cygni itself marks a break in the flow. Just south of 52 Cygni is a 10 arc minute discontinuity followed by a far less laminar remnant. This southern section swings to the east and takes on a broad-tailed diaphanous look. This section is frequently broken by the darkness of deep space.
If you are able to make out the features of the Western Veil, you will be happy to know that the Eastern Veil Nebula (NGC6992) is much more observable. However, you should also know that, unlike the Western Veil, the Eastern Veil is less recognizable when found. (Here again an OIII filter is very effective in revealing the nebula by significantly reducing the amount of broadband star light in the field of view.)
To locate the Eastern Veil, start by slewing 52 Cygni to the southernmost station in your 50X FOV. (This offsets the center of the eyepiece roughly 30 arc-minutes north.) From there, slew due east roughly 5 degrees. As you slew, you may notice various "patches" of reflective nebulosity. This will be followed by a large dark gap. Once the gap is crossed, a huge increase in the number of patches (to a point of rich profusion) is seen. This profuse nebular region is the "broad-tailed diaphanous" corrspondent to the one seen at the southern portion of the Eastern Veil Nebula.
Although this south eastern veil region is quite intricately complex and beautiful to view (again with filter) I found myself quickly swinging north and following the much more luminously continuous "winged" section of the Eastern Veil. This eastern version of the "wing" is much larger and brighter than the corresponding western wing. (The western wing filled about half the field of view in a 1 degree eyepiece.) The eastern wing extends more than a full degree and really needs a super wide field eyepiece to display it properly. (This alone might almost be worth the price of an SWF eyepiece and 2"star diagonal...) Unlike the western wing, the eastern wing hints at more featherlike detail. Hours could easily be spent roaming over it or attempting to create an eyepiece impression with pencil and paper.
After having finally really seen both the Eastern and Western Veils, I'm almost ready to give up globular clusters as my favorite deep sky delight.
The Pup and Veil Complex:
(From The REAL THING!
)
Now for the Pup and the Veil Complex: God, you have to love four degree views of the sky! Thread in an OIII bandpass filter. Drop in the 35mm Ultrascopic for 13X and you can pull in the three remnants of a star that died tens of thousands of years ago. A star which probably lit up the entire cosmos with the luminosity of an entire galaxy. A star that fulfilled its all too brief career as midwife to thousands of other dimmer Suns - each with its own special destiny to illumine the "dark matter" of space and give birth to time and home to sentience...
All three portions of the Veil Complex were possible. The Eastern Veil (NGC6960) wended its way from the brighter, tightly flowing stream some half a degree south of fourth magnitude 52 Cygni and spilled out into the wider, diffuse delta of nebulosity to the north. Meanwhile, some two and a half degrees west, large and "feathery" NGC6992 curved outward away from the eastern remnant. Long and more contrasty, the Western Veil's northern section is quite dense, and well-defined. South of a tenth magnitude field star, the dimmer southern region displays vague hints of delicate detail. Both of these sections are far wider and more luminous than the Eastern Veil. Finally, about halfway between the the Eastern and Western Veil, and much more difficult than either of the two, is an extremely diffuse, half-full-moon-sized remnant. This somewhat north of the bright sections of the two main nebulae. This "Northern Veil" (NGC6979) can be found by extending the curve of the Western Veil northeast. Just to glimpse it, even with averted vision is enough to satisfy a longing to encompass the entire complex in a single view... But beyond this, 80mm Pup was even able to show me a wee bit of central brightening. How much more will be possible on the darkest of nights as the Swan glides effortlessly overhead later in the Summer???
Argo, Other Scopes, and Veil Complex:
(From We Gaze Not Alone)
Finally Cygnus rises far enough out of the Felton lightdome to become susceptible. And with Cygnus, the Veil Complex.
Here we all struggle. Old threads perhaps not well woven must be taken up anew. Finding the true 52 Cygni can be quite difficult when cobwebs take residence from lack of constant occupation. 41 Cygni kept coming up. This pretender constantly disappointing us all with it's lack of adjacent nebulosity. Eventually we caved and turned to our charts. 52 was found in the sky - but no thin small scarf of luminosity was in attendence. On with the OIII filter. Ahh, such smoothly flowing beauty and grace. At 50X, the nebula extended across Argo's field of view. Diaphanous, fluidic and supremely subtle - one part of a much more complex dying gift of an ancient star who in passing flooded the Universe with the Luminosity from the Single Source.
The Takahashi (FS102 - 4 inch apochromatic refractor) too showed it well. With OIII filter in place and 25X eyepiece, the Western Veil was even brighter and well-delineated than in Argo.
Repeated efforts finally located the brighter Eastern Veil. It spilled completely outside Argo's 1 degree field, but took up complete residence in the Tak at 25x. The view of this remnant of the Star that Gave was more obvious and replete with structure than I have ever seen before through Argo. With or without the filter, it remained instantly apparent and intricately emboidered onto the night sky. The entire crescent easily fit within the Tak's 2 degree field of view. Pinpoint stars accenting the wispy nebulosity like the background of a painting by one of the Old Masters.
Argo, Other Scopes, and the Great Nebula of Orion
(From General Public Cordially Invited)
Even with the moon up, transparency was pretty good (for this particular locale). To the unaided eye, Iota Cassiopeia was just direct (ULTM=4.6). As the night progressed (especially after moon-set), I would say (light domes of Santa Cruz - southwest - and San Jose - north - notwithstanding), transparency improved to an ULTM of 5.0. Interestingly enough, later in the evening, I had a visitor who asked me what I thought of sky conditions. With my usual enthusiasm for this topic, I approached an answer by explaining how I usually assess the sky based on stars in Cassiopeia and how this translated into what I would later be able to see through the scope. I made the especial point of saying that I needed good dark nights (ULTM>5.0) to get the kind of deepsky views my neighbor Ralph and his 10 inch scope would get even on "poor" (ULTM<4.0) nights.
This drawing of the Great Nebula in Orion was done March 9, 2001 and does no justice to the view through either Argo or the Pup. Despite a poor sky, and my own lamentable drawing skills, you can at least get a sense of the location of the "Tongue of Darkness" (above left of the Trapezium star group) and the "Darkness Cliff" (slightly below and right of same).
My other neighbor - Jeff - had setup a four inch NextStar "next door". We took a look at M42 in his scope, followed by mine, then Ralphs. The NextStar could just barely reveal the 7.9 magnitude member of the trapezium. (Unforunately, the ep's FOV was "curved" and the trapezium could only be resolved near the center of the field.) Nebular gases were gray and less expansive than in the six inch. The tongue of darkness licking at the Trapezium lacked depth of contrast. There was no sense of the dark slash of absorption nebulosity opposite the trapezium from the tongue behind it. The six inch showed the bright nebula as "white" rather than "grey". The trapezium was visible no matter where its position in the FOV. The dark slash was just visible with averted vision. The ten inch showed the dark slash obviously. (In fact I had first noticed this feature in the ten inch, then traced my way backwards through the series of scopes to determine where it was lost. I had never seen it before in my six inch.) The ten inch also showed only the four main stars of the trapezium - stability was just too poor for detecting any others.
The Pup and Great Nebula of Orion:
(From Fun with the Pup)
Sadly, Orion is now rapidly leaving for points west. So to catch it before it's dissappearance, I quickly turned the Pup on the Hunter's sword and centered The Great Nebula in the 132X OIII field of view. Superb! Even with the sky visibly moonwashed, I was able to see tenuous folds and rifts. Surprisingly, the darkness cliff west of the Trapezium was directly detected. The Trapezium displayed all four main stars. To the north and east, nebula M43 was easily made out. Further north, the four star arch embedded in bright nebulae NGC 1973-5-7 was also visibly entangled. Above that, "Pi"-shaped cluster NGC1981 showed about a dozen 6 through 10th magnitude stars, a subtle hint of nebula enshrouded all its members.
the Pup and the Pleiades:
(From Fun with the Pup)
The Moon was now about a third of the way up the sky to the southeast. I concentrated on a lowering Taurus and Auriga in the northwest. My first look was M45. The Pleiades are an example of the kind of deepsky object the Pup excels at. Lot's of bright stars spread over a 2 plus degree field, embroiled in low surface brightness nebulosity. Tonight, however, between the brilliant moon and Boulder Creek lightdome, there was no suggestion of nebulosity. The stars were bright, but backdropped by a deep blue - not indigo black - sky. One thing I did notice (something that is beyond Argo due to its narrower field of view) is the central position that 3rd magnitude Alcyone takes in the cluster.
the Pup, and Open Cluster M50
(From The Pup Pulls His Weight)
M50 in Monoceros, north and east of Sirius is the perfect object for an 80mm scope. It can just be detected as a swatch of light in the 6x26 finderscope. Turning to the main tube at 16X, a small, elongated scintillation in the field captures the eye immediately. At 44X, a half-dozen stars in a similar field can be caught with averted vision. It is only at 132X that M50's clusterlike nature can be confirmed. And this only at the price of great concentration by the observer. M50 is probably better suited to 100mm scopes, but in my estimation, on a reasonably dark night (ZULTM=5.0) it can be observed to satisfaction in a three inch refractor with fine optics.
Members of M50 begin at about magnitude 9.5 and go on down from there. The Pup probably showed about 2 dozen stars, few of which could be directly acquired without bowing out. The main group of stars is quite globular in appearance. At 132X that globularity appears encased in a triangle. The triangle fills about one-half the field of view. The core, at half that size, is displaced to the north. One tip of the triangle leads the cluster across the sky. Trailing this assemblage, just outside the 132 X field, is a blue 7.5 magnitude field star.
Argo and M50
(From The Plan)
I had also taken a look at open cluster M50 through the Pup. At cumulative magnitude 5.9 and apparent size 16 arc-minutes, M50 proved to be just barely resolvable at 132X. Since M50 is included on the 100mm scope list, I was very pleased with the result - especially given it's more southerly sky location. Under Argo's gaze, and slightly poorer conditions of this evening, the dozen or so stars seen by the Pup exploded into a group of perhaps fifty or sixty. And this at 50X! At 120X perhaps one hundred 10 - 13th magnitude stars were visible. The clusters shape also revealed itself. Like M35, it appears flowerlike. In this case though, the flower is rotated away from the viewer about 45 degrees. Also instead of a number of rose-like petals, this particular "flower" shows three, all oriented toward the northeast. A lovely sight.
Argo, The Pup, and the Great Hercules Cluster:
(From Pacific Ocean Marine Layer Subsides)
An eyepiece impression of the Great Hercules Cluster sketched in pencil May, 24, 2001. This gives an idea of how Argo shows the cluster under decent but, less than ideal, skies. NOTE: While scanning and compressing the original sketch, certain artifacts may be introduced. These may be virtually indistinguishable from actual detail seen in the cluster.
Basically, under 5.4 ULM skies (local to M13), 150mm Argo (at 120X - 15mm Ultrascopic eyepiece) resolved hundreds of stars using moderately averted vision - many right across the clusters core. Meanwhile, when looking at it direct, probably one hundred stars could be held direct - several on top of the core. In addition, much star-chaining was possible - especially arcing outward to the north and south from the core region. (This gives it a "scarab" appearance to my eye.)
Through the 80mm Pup and also at 120x (10mm Ultrascopic with 3x barlow), maybe 75 stars could be seen scintillating on eye movement. Some 2 or 3 dozen could be held with moderate aversion, and a handful were possible direct. There was no evidence of star-chaining whatsoever.
Argo, The Pup, and Various Summer Globular Clusters
(From But for a Stable Southern Sky
)
M10 Through Pup: "Scintillates direct using soft eye technique across core. (No need to avert whatsoever to see a dozen or so stars on the limit.) Under moderate aversion, dozen or so stars held direct. The globular is definitely blue (as opposed to grey at 43mm.) Where no outlier / field stars were seen near the frontier at 43mm, perhaps four or five could now be seen. Overall this cluster showed best with some aversion of the eyes...
M12 Through Pup: Perhaps a dozen stars scintillate on soft eyes. Two dozen held on aversion. Several outliers hinted at using the 43mm are now obvious. Less blue than its confrere. But due to looser constitution the cluster is more satisfying to the eye in an 80mm scope at 120X using direct "soft eye" contemplation. M12 is effectively closer to resolution.
By this point sky depth is now slightly better - certainly 5.0 - but Ophiuchus will soon duck out behind the tress. So quickly, 150mm Argo's turn at 120x...
M10 Through Argo: Large shaft of stars skewer the core along north-south axis. (Otherwise, the cluster appears quite round for a globular.) Blue color quite obvious. Two dozen stars held direct without real effort. Several even seen before the core. Truncation to west very obvious. No sense of star chaining, but still a fine, partially resolved view through a six inch scope.
M12 Through Argo: Very elongated and indistinct core region - oriented north-south. Obvious linear shaft of bright stars also running north-south at core west. Not quite as blue as - and certainly not as condensed as - M10. However, more stars seem held direct using "softeye" technique. Has a more populous field - including a "cochlea spiral" of eight or nine eleven to thirteenth magnitude field stars. (These originate from the north, arc east, and unwind to the south.) Quite possibly a precursor to "star-chaining".
Both clusters gave fine views through Argo - no special techniques needed to see dozens of members. Blue color obvious. M12 less distinct core and is more open. M10 rounder, more obvious core, and compact. Both clusters have integrated magnitudes of 6.6. Both extend 12 arc-minutes in apparent diameter. Each bears an average surface brightness of 11.7 - yet one (M12) echos the brighter, more open and elongated M4 in Scorpio. While the other reflects the more classically globular, brighter, condensed M5 in Serpens.
However, there is the small matter of the "rolling pin" bisecting M10's core, and the "needle of stars" within M12. These features are more like the "String of Pearls" seen across core M4...
Later, turned Argo - again at 120x - on M92 in Hercules. (Great Cluster's sibling.) At magnitude 6.5 and diameter 11 arc-minutes, M92 has an average surface brightness .3 magnitudes more luminous than the two Ophiuchan clusters. Add to this M92's superior sky position (ZULM=5.5) and one would expect it to give the superior view. In fact, even at 120X, M92 showed subtle - but perceptible - "star chaining". This particular feature is only seen in the very finest half-dozen or so globular clusters visible in the sky (while using a 150mm scope from 37 degrees north latitude).
Argo, Other Scopes, and Various Summer Globular Clusters
(From SCAC Star Party Potpouri)
By skydark, neighbor Dean and I were off and running comparing globular clusters through the 150 and 200mm scopes. In every case, the extra 50mm of diameter gave visibly brighter images. Resolution of globular components was also slighly better - due specifically to the extra magnitudinal reach of the scope. I've now compared Argo's views two 8 inch Meade SCTs at SCAC star parties. Dean's LX50 and Dwight's LX200 have both acquitted themselves honorably. Argo's views of globular clusters are perhaps a tad closer to SCAC club member Dan's FS102 Takahashi Apochromat than to Dean and Dwights pair of 8 inch SCTs. This amounts to another good reason to have Argo's surfaces coated with high-efficiency surfaces and upgrade the mirror diagonal. Such changes would clearly shift Argo more toward 8 inch performance in terms of light gathering.
At left is an eyepiece impression of Globular Cluster M5 in Serpens done July, 8, 2001 through 150mm MCT Argo. All the usual caveats apply.
Dean and I started out west with the fabulous M5 globular in Serpens. Both scopes showed at least one hundred stars across the core at 120x. From there, moved on to the "Twin Clusters" M10 and M12 in Ophiuchus. It was here that I noticed something unexpected: The clusters really aren't "twins". M10 appeared considerably rounder and more condensed than M12. A significant amount of resolution was seen in both clusters - certainly several dozen stars. But M10 gave an appearence more like M5 seen before it. No question. I'll need to spend some quality time with these two clusters to really make a definitive comparison.
NOTE: This set off the comparison of M10 and 12 done in the previous extract that actually came out of a later report featuring the Pup and Argo.
While Dean mounted a camera on his scope (for a star field capture), I spent a good deal of time on globular M14. On such a good night, hoped to get a better sense of resolution. Backyard Boulder Creek's views to the south tend to be a bit marginal. As previously mentioned, seeing is exceptionally good to the south at the Bonny Dune site. Here follow a few field notes on M14 from last evening: "Large elongated core region oriented east-west, brighter to west than east. Two or three dozen stars hang right on the threshold of visibility at 120 and 180X..
Contemplated globular M9 as well: "Elongated core region. Center offset west. Dozen stars visible under moderate aversion at 180X. Best view of the cluster at 120X."
From M9, dropped south to Scorpius and M4. Numerous stars resolved. The six or seven that make up the"String of Pearls" across the core were quite evident. Next: M80 - very small and condensed. Only a handful of outliers possible at 180x. This has been and remains one tough customer! Needs more aperture and higher magnification to reveal anything of its mysterious goings ons.
Had two views of incomparable M13 during the evening. Dean turned it up in the 200mm. - Slightly brighter view of that normally seen through Argo. Jack turned it up in the 14 inch Dob! Simply incredible - must have been a thousand stars visible. HUGE! Star chain effects down played due to the many faint members filling the voids outside the core. As fine an instrument as Argo is for use with globulars - aperture continues to make the difference between presence and PRESENCE. You just don't have to work very hard at anything when using one of these big scopes - nebulae, clusters, galaxies - eveything except double stars and planets. (This is where smaller scopes tend to excel.)
The M71 globular lay well overhead at the time. Sky looked extremely dark in the eyepiece. The globular's field may not be as rich in stars as the Milky Way - but is nevertheless well populated. The cluster lies 20 arc-minutes due east of a sixth magnitude star. A ninth magnitude star lies just south of its visible frontier. Perhaps 3 x 4 arc-minutes of the cluster possible. At 50x, starlike core - but higher magnifications (120x) showed this to actually be a star (of about the 13th magnitude). The interesting thing about the cluster was the unexpected number of stars lying directly on its line of sight. In fact, one string of 13th magnitude stars cut east-west right across the cluster's core. (These were only visible at 180x.) Assuming the bulk of the stars seen in and around the cluster are members, then M71 is probably the dimmest cluster yet viewed that shows obvious resolution.
Argo and Galaxy NGC4565:
(From Missing Messier Found. Mystery Resolved?)
An eyepiece impression of Edge-on Galaxy NGC4565 executed May 23, 2001 through 150mm Argo. Perhaps a dozen edge on galaxies of this class - ranging from M82 (Ursa Major) to NGC7331 (Pegasus) - may be found throughout the heavens. Unfortunately, all too few a number to support the galactic aspirations of six inch scopists!
Galaxy NGC4565 Coma Bernices, Magnitude: 9.6, Size: 15x2', ASB: 13.3 Wow, I love edge-ons! This one is large, bright, and sharply delineated. A classic. Don't miss this one folks! Could make out almost 10 minutes of its length. Lenticular edge oriented along northwest to southeast axis. Galaxy nicely framed by a trio of 7th and 8th magnitude stars. At extreme aversion could just make out its star-like nucleus (70X). Add to this an obvious core region, a bright line of luminosity along the spine, and you have a beaut. The frontier of this galaxy is sharper to the west and softer east. A wispy halo east of core. If I were an intelligent octopusal alien, I'd give this one "eight thumbs up".
Always Room for Improvement
Admittedly, its rare to get such a lengthy and detailed "comparo" between a variety of scopes and apertures in a single report. But, over the last year or so I've had numerous opportunities to study the sky through a number of scopes and get a sense of capabilities under differing seeing conditions. Add to this an extensive archive of reasonably well-documented observations (right here on astro.geekjoy), and some kind of extensive discussion - such as the above - becomes feasible.
My hope is that you got the sense that there are better small refractors (in terms of optics) than the Pup. There are also scopes whose superior aperture and half-way decent optics give superior views of deepsky studies than Argo. In terms of scope types, the Takahashi FS102 (4 inch apochromatic refractor), offered views quite comparable to 6 inch Argo. AND under less than decent sky conditions, the Tak actually gave better views - according to my recollections.
Not referenced above was a particular star party where I had a chance to compare views between the Pup and a Televue 85 apochromatic refractor. That star party (see "A (Long) Night Under the Stars" and later views through the FS102, showed me that a world of difference exists between 85mm's of aperture and 100. So somewhere between 85 and 100mm there is a line to be crossed when it comes to the type of views you get.
Something else of note: Initially, Argo gave deepsky views comparable to a 200mm SCT. (See "Star Party Shootout" That scope, however, needed a good cleaning of the correcting lens before it was able to overmatch the 6 incher. Initially that same scope gave planetary views similar to Argo, but sometime after clean up, collimation went astray and it could no longer match Argo's - or a lesser aperture 5 inch MCT's - views of the Gas Giants (despite a very fine sky).
There were opportunities to view through 14 and 16 inch dobsonians. Neither scope had especially good optics. Much of this may be attributed to short focal ratios related difficulties achieving proper collimation. BUT when these Big Un's were turned on sky-stuff where quantity of light is more important than quality - even I lost my preoccupation with such trivialities as coma and astigmatism!
Through such scopes galaxies and extended nebulosity gave better detail direct than Argo revealed on the very finest of nights employing every degree of averted sight feasible. These scopes often made obvious to the eye what was vaguely hinted at through 6 inch Argo.
The Show Goes On!
Those of you who would like to delve into specific issues I've had over the months with both the Pup and Argo may like to make a hyperleap to the following pages. Things have not always been so keen between me and the scopes. We have been down a road together and other improvements are possible in the future.
Read On!