NGC6888: "The Crescent Nebula in Cygnus"
NGC206: "Brilliant Star Cloud in M31"
NGC604: "Great Nebula of the Triangulum Galaxy"
Omicron Persei: Close Double of Disparate Magnitudes
NGC1245: Dim Open Cluster in Perseus
Companion of Aldebaran
NGC1300: Face On Spiral in Eridanus
Mu Ari: Wide-ish Double of Disparate Magnitudes

NGC6888 "The Crescent Nebula in Cygnus"

This reflecting nebula is easily confused with "star haze" caused by light scatter in a highly populated region of Cygnus. Complicating the search is the fact it is quite large and has an undetermined, low adjusted surface brightness. Lacking a published photographic magnitude, it is difficult to even say what the Crescent's average surface brightness is. Simplifying the search though is the fact the asterism of stars associated with 6888 brightest components is easily identifiable - once the asterism is itself located - just off the spine of the Cygnus Cross. Reports are that a 200mm is needed to show it. But I rather suspect that smaller apertures can reveal it in very dark skies, of low light scatter using a 30X ep. Send me an email when you find this baby. Be careful to note the limiting threshold magnitude of the sky and the magnification of your scope and its aperture. Using this info I can get an idea of its photographic magnitude.

Hold those emails. For I have seen the Light! And what a faint light it is... With the Moon moving in to second quarter, I decided to follow an example set by others and get up early in the morning (3am) after moonset and observe the Summer Triangle - a little out of season. During the course of the morning I toured many of my (and probably your) favorites - M13, M57, M27 - from the backyard. As it turned out, NGC6888 was the last adventure of the morning. For you see, after having positively acquired the Crescent Nebula in the region just west of the Swan's spine, "Rosy Fingered Dawn" touched the sky - and that was that.

Conditions were quite dark - for backyard, downtown Boulder Creek. Before locating the Crescent I was able to hold the 13.0 magnitude star bordering the Ring Nebula with slight aversion. Based on this, and the fact that the brightest parts of the Crescent were also visible using the same visual trick, I've determined that the Crescent visual magnitude is approximately 7.0 with an average surface brightness of 13.6. Thus most clean 6 inch scopes should reveal faint nebulosity with slightly averted vision in the region of the asterism shown at right under 5.5 plus ULTM conditions.

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NGC206: "Brilliant Star Cloud in M31"

Just found 206 this very evening. To locate it in a 6 inch you really have to know where to look and what to expect. At lower search magnifications you will basically see a "mound of ill-defined luminosity" just at the limiting threshold magnitude for a 150 scope at 70X magnification on a 5.0 ULTM night. Higher magnifications will give a sense of the "rectangular" shape reported in the books. There are probably other such regions in M31. Might make an interesting project to map them out -- after you've turned up all the usual deepsky subjects, of course. Check out the triangle shaped asterism to the lower left of the star cloud (mid-lower right triangulating with M31 core an M32). Notice the other stars around the triangle. Finding this asterism is the key. (Keep in mind your FOV may be inverted or flipped from mine. I've doctored the image to diminish the brightness, contrast and orient things the way I see them in my scope.)

BTW: I have not found a reported photographic magnitude for 206. Assuming the optimal scope size is 250mm, this star cloud has an "empirical" photographic magnitude of 13.2 (using new "revised" methods based on published angular size of object by type.)

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NGC604: "Great Nebula of the Triangulum Galaxy"

Finding NGC604 is another instance of knowing where to look and what to look for. Early on I spent a huge amount of time sweeping way outside the core of M33. (I assumed it was as extensive as M31 when in reality the whole thing sits inside a one degree FOV.) Later I did the research using astrophotos on the internet. This confirmed that one asterism in particular I had noted was very near 604. Prepped with this info, I was able to hone in on the locale. Finally, under decent conditions (ULTM=5.4) I made the find. When evaluating the astrophotos it became pretty clear to me that the surface brightness of 604 was about the same as the brightest part of M32 core. Unfortunately when I began my search I was looking for something much brighter than the core (certainly more compact). This false sense of expected "brightness" (like information I had read about NGC206 being a degree and half away from M31 core) caused me a lot of problems. Only goes to show that sometimes you gotta do your own homework...

NGC604 was a much easier view than NGC206 in M31. The 150mm even came close to revealing shape and orientation. Assuming that a 200mm scope would just give the last bit of light grasp needed to reveal such characteristics, and based on published angular displacement of 2X1 arc-minutes the bright nebula NGC206 has an empirically arrived at photographic magnitude of 12.4.

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Omicron Persei: Tight Double of Disparate Magnitudes

Omicron Persi consists of a 3.9 magnitude primary and a 8.5 secondary separated by 1.0 arc-seconds. The difference in magnitude means that a large-apertured scope with excellent, clean, dew-free optics is required to make a clean split. Without saying, sky conditions would also have to be unusually fine as well. Information about this split would prove extremely useful in fine-tuning parameters within the Double Star Resolution Calculator. Any information I come by will be posted here. Please feel free to email me should you "make the split". Information about scope size, type magnification and especially seeing conditions (ULTM and stability) would be extremely useful.

NOTE: During an attempt to split Castor (on a poor seeing night) I found (unexpectedly) that an OIII filter does an outstanding job of suppressing light scatter from bright stars. Omicron's secondary is fairly dim, but it is more than one magnitude brighter than the threshold magnitude limit (of magnitude 10) imposed by my OIII filter. Once the weather clears up I hope to determine if the use of the filter will reveal the secondary...

BTW: The latest version of the Double Star Separation Calculator says that, on an excellent stability night, a 315mm (12.4 inch) apertured scope should just split this object. Whew! The same calculator says that Sirius A and B can be separated by a 200mm (8-inch) scope when at widest separation (11 arc-seconds). This is next expected to occur in 2025. (Literature on Sirius double resolution does in fact support this calculation - so it isn't necessary to wait 25 years to verify the calculator in this regard.)

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NGC1245: Dim Open Cluster in Perseus

1245 is an open cluster of 100 - 200 stars with an integrated magnitude of 8.4 and 10 arc-minute angular displacement. During my first effort to find 1245, I thought it was brighter (magnitude 6.9), larger (almost a degree) and sparser (40-50 stars). The object I turned up is probably 1 degree north of the real 1245 and makes for a pretty poor cluster. Due to it's poor visual characteristics (no core, extensive voids) I decided to do a little research on the web. One site quoted figures similar to those of the original 1245. Most cited the preceding smaller/dimmer values.

One interesting fact cited on the Internet was the fact that the brightest 1245 stellar component is mag 11.1. Since the initial search was done during a lunation cycle, such a star (not to mention even dimmer stars in the cluster) would be very easy to miss. So to recognize such a cluster as a cluster would require a solid telescopic 12.0 + magnitude seeing night. In searching for such an object, I would also hope to see a group of at least half a dozen stars against a background of "star haze" as well. This baby could definitely prove more elusive than it's 8.4 integrated magnitude suggests!

BTW: The latest version of the Deepsky Visual Brightness calculator calculates that, on a 5.5 ULTM night, a 71mm (2.8 inch) apertured scope should just detect this object. But one caveat, you have to know where to look and precisely what to look for when the brightest star in a cluster is magnitude 11.1.

NGC1245 Found: During a trip to China Ridge on Thursday evening February 15, I managed to conclusively track down NGC1245. Having become familiar with the image above, it was fairly easy to identify the keystone of stars that encapsulates it. Under 4.5ULTM conditions, "I noticed a 15 arc-minute sized keystone of stars that looked suspiciously like what I had seen in photos. Near the southern corner of the keystone, scintillation of two or three 11+ magnitude stars appeared. Switching to 120X (15mm Ultrascopic) I could directly acquire perhaps three of the stars. I could also make out the scintillation of perhaps a dozen others (as I flitted my eyes across the FOV)."

Companion of Aldebaran (Alpha Tauri)

Aldebaran (Arabic "The Hindmost") is an orange-red star of magnitude 1.0. It is conveniently positioned well up in the sky near Jupiter and Saturn this month (February 2001) in the early evening sky. Aldabaran is known to have an 11.1 magnitude companion. One quick reference guide I possess (simply entitled "Seasonal Star Charts" distributed through Orion Telescope and Binocular) describes the component as separated by an angular distance of 31 arc-seconds. Reverend TW Webb's "Celestial Objects for Common Telescopes" cites an object of similar magnitude but at a distance of 109 arc-seconds. This latter object, is easily seen in the MK-67 at all magnifications and under any reasonable seeing conditions. This star is itself a possible binary (separated by roughly 2 arc-seconds) consisting of an 11th magnitude primary and a 13.5 magnitude secondary -- a good test for any scope and observer on any night. (I'd like to hear from anyone who splits this one and the conditions under which it is possible as well.)

Webb credits Burnham as discoverer of a closer 31 arc-second attendant of Aldebaran. This component displays the same proper motion and probably makes of the Hindmost a true double. This particular star is that of main interest here. In several attempts, I have yet to resolve this object. Obviously the difficulty is not separation. It is the low luminosity of the secondary within the expansive light scatter of the first magnitude primary. A problem compounded by the amount of moisture in the air typical of the Santa Cruz Mountains this time of year.

Interestingly enough the Double Star Resolution Calculator suggests that the Aldebaran split will require a night of fair stability and a local ULTM of 5.3 in a 150mm MCT (such as mine). Recommended magnification is 70X. To be honest, I may not have even observed Aldebaran under such conditions (over the last several attempts), but the fact that I have not seen the secondary prompts this post.

NGC1300: Face On Spiral in Eridanus

NGC1300 is located about 2.5 degrees north of Tau4 Eridanus - a region of 4.5 magnitude stars some 30 degrees above the southern horizon just after astronomical dusk in the month of February. At magnitude 10.4 you might suspect that a scope capable of revealing 13th magnitude stars would make pretty short work of NGC1300. But the fact that it is on my "Most Wanted" list suggests that something is amiss. So let's start by gathering a few clues...

NGC1300 is a face on spiral galaxy some 7 arc-minutes in length and 4 arc-minutes in width. It's per arc-minute 60x average surface brightness is magnitude 13.9. Half of 1300's perceptible luminosity should be visible in any scope capable of revealing stars of magnitude 13.9 through a 60X eyepiece. Employing The Telescopic Limiting Threshold Calculator we determine that a 350mm (14 inch) should show this brighter half through a regional 5.5ULM sky.

But we don't really need to see half of 1300's light to find it. This kind of deepsky reach is needed to plainly reveal structure. So we turn to The DSO Visual Susceptibility Calculator to determine the magnitude of the brightest part of 1300. To do so, we plug in the magnitude and apparent size of 1300, and select it's type (Galaxy Condensed). From this we learn that at 60X, the brightest part of NGC1300 shines at about magnitude 11.8. Prepped with this information, we go back to The Telescopic Limiting Threshold Calculator and determine that the minimum scope size that will reveal magnitude 11.8 stars (at 60 X through 5.5 ULM skies) has an aperture of almost 120mm.

We'll happily, I have a fine 150mm scope - but still 1300 eluded me. Where'd I go wrong? Well first, it's very rare for winter skies to go as deep as magnitude 5.5 some 30 degrees above the horizon (where I observe, anyway). So if I want to "get real" I have to plug practical values for transparency. So I use the Telescopic Limiting Threshold Calculator to figure out the lowest ULM sky that enables a 150mm MCT to detect 11.8 magnitude stars direct. Assuming fairly stable seeing (6/10+) - and a 60x eyepiece, that "magic number" turns out to be "5.2".

Now all this is well and good, but the opportunity to locate NGC1300 under such conditions never occured during 2001. As it turned out, by the time I had a good handle on the galaxy's precise location, weather, Moon, and season all conspired to allow Eridanus to slip too far west for success.

This brings us to the 2002 viewing season...

During Northern California winter months, skies are typically half magnitude less transparent than the remainder of the year. Due to rain and overcast, few opportunities to track down "on the edge" elusives such as NGC1300 also exist. (This has been particularly true of the late 2001 autumn and early winter seasons. However, last night (Saturday, January 12, 2002), gave me a chance to get away from the gauzy skies above Boulder Creek and visit the perceptibly deeper skies over rural Bonny Dune. There, some 1500 feet above the fogs and miasmas below, stars to magnitude 5.5 could be held direct on the zenith. Meanwhile, it was possible to fully follow the great flow of River Eridanus outside the Santa Cruz light dome to the southwest. Certainly stars to magnitude 5.0 were possible unaided...

While engaged in the general comraderie of fellow amateurs, I searched for face-on spiral NGC1300. Navigation was the same used (so many times) last season. Pick out Tau-4 unaided (in the lower stretches of the Great River). Center the finder. Slew three degrees north to 5.3 magnitude SAO 149063. Locate the sixth magnitude finder star some 30 arc-minutes south and east. Monitor the low power (50x) field while sweeping due south some 20 arc-minutes. And there, with guide star near the edge of that same one degree field, was just able to detect a surprisingly large (3X5'), southeast-northwest oriented, smattering of vague luminosity. Averting my vision strongly, could also see hints of a starry core within a wispy region of central brightening.

That's it, NGC1300...

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Mu Ari: Wide-ish Double of Disparate Magnitudes

Like Aldebaran, Mu Ari is a member of a class of double stars that are widely disparate in magnitude. Unlike Aldebaran, the primary itself is not particularly bright, but is bright enough to make definitive recognition of a very dim secondary a challenge. The following is from a report dated Friday, January 19, 2001:

Mu Ari is located about 2 degrees northwest of Pi. Both Mu and Pi are brighter members of wide line of sight doubles in the finderscope. Mu consists of a 6th magnitude primary and relatively distant (19.4 arc-second) 12.5 magnitude secondary. Despite the relatively wide separation, I used the 10mm Ultrascopic ep (180X) to offset the secondary's dimness. Even this approach was not enough to conclusively make out the secondary in the FOV. (The sky by this time was quite dark - 5.4 ULTM.) Certainly the light smear from the 6th magnitude primary washed the dimmer secondary completely out. It's possible that 360X may have revealed the secondary -- although barlow lenses damp out magnitude-magnification effects somewhat due to additional elements in the light path.

Under 4.8 ULM skies and through variable clouds (sucker holes), I revisited this pair almost one year later. The primary showed a sweet little 6th magnitude airy disk at 180x with just a hint of a first diffraction ring. Some 20 arc seconds almost due west (but slightly south) of the whitish primary I made out what appeared to be the faint twelth magnitude companion. To be sure that companion was faint and required some very slight aversion to confirm. Not knowing the position angle of the pair made it a cinch to confirm detection. And sure enough consulting http://www.alcyone.de/SIT/bsc/HR0793.html, I was able to verify the secondary's position just south of due west (PA=264 degrees - 1878).

What concerns me (a trifle) is why, under better conditions (5.5ULM) this time last year, I failed to detect any sign of a secondary. Certainly the sky on the evening of detection was problematic (in terms of transparency). But I must admit, despite intermittent (and quite extended) clouds, the usual "star haze" seen around sixth magnitude stars was not apparent. There is also the matter of Argo's improved alignment and finally a year's worth of experience with disparate doubles can not help but improve one's perception...

One allied mention - I have yet to turn up the closer (31 arc-second) 11th magnitude companion of Aldebaran. This despite a search for it on this same night. According to http://www.alcyone.de/cgi-bin/search.pl?object=HR1457 this is supposed to be the "E" member of the Aldabaran group, but unfortunately no magnitude is specified. (The 109 arc-second C component is cited as magnitude 11.3. On the evening in question it could just be held direct with aversion in the bright primary's glare at 70x.)

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