The Basics: Macro Features
Fine Detail: Micro Features
Labeled CCD Image of Jupiter (with Satellite Transit)
Unlabeled Sketch of Jupiter
Fill in the Blanks!
What 9 of 10 Seeing & Good Optics Makes Possible
And What Poorer Seeing & Good Optics Doesn't...
And Limitations Imposed by Aperture.

The Basics: Macro Features

Like all the nearer planets, Jupiter shows a disk. In fact, Jupiter's disk is the largest normally visible in the solar system. (Venus' apparent size can be larger - but only as a thin crescent - not a disk.)

The shape of Jupiter's disk is a bit unusual. It appears visibly "oblate" through the eyepiece. Jupiter's minor axis is roughly 90% the diameter of its major axis. That minor axis lies along the planet's central meridian. Its major axis of course, lies along the equator. Because the planet is so oblate, special blanks are needed for drawing purposes. Example blanks are available at the Association of Lunar and Planetary Observers (ALPO) Jupiter Section .

Like all disks, there is a visible transition from the edge to space around it. That transition is the planet's "limb". The clarity and sharpness of Jupiter's limb is the first clue visual observers get as to how well they will see Jupiterian features. Scope size, type, obstruction ratio, optical quality, selected magnification, and optical alignment, plus high and low frequency atmospheric stability all impact how sharply limb-focus can be achieved and subsequently how much detail can be seen on its "surface".

As we all know, Jupiter's true "surface" is hidden from us optically. We see only atmospheric formations caused by powerful forces unleashed by the planet's rotation and effects of temperature variation on constituent gases (which can be quite complex molecularly). But just because we can't see the planet's "surface", doesn't mean there isn't a lot to see.

Details on the disk of Jupiter are divisible into two main categories. On one level there are "macro-features". Macro features are analogous to the kind of things seen on the Moon without optical aid. This is "big stuff". Even a super-modest scope (50mm) will show some of these. Two such macro features have already been mentioned - the disk and the limb!

But of course there are others: At higher magnifications, a 50mm scope will divide the planet's disk into five main features: Equatorial Zone (EZ), North Equatorial Belt (NEB), South Equatorial Belt (SEB), North Polar Region (NPR), and South Polar Region (SPR).

Depending on seeing and optics, a 75mm scope may add four more: North Temperate Belt (NTB), South Temperate Belt (STB), North Tropical Zone (NTZ), and South Tropical Zone (STZ). So once we start increasing optical reach, things begin to get a bit more complicated.

Jupiter's macro features are of two types: "Bright" and "dark". The two polar regions, temperate and tropical zones, and the equatorial zone are all examples of "bright" macro-features. Contrasting with these are the dark "belts". Belts vary a great deal in thickness and contrast. Various thicknesses may also be seen among the various bands, zones, and regions as well.

Through a steady sky, three other "belts" may be visible through high quality 150mm reflectors or 100mm refractors. These are the Equatorial (EB), North-North (NNTB) and South-South Temperate Belts (SSTB). A total of 7 belts may therefore be seen running parallel to the planet's equator. Between these seven belts are six band-like zones: North Equatorial (NEZ), South Equatorial (SEZ), North Tropical (NTZ), South Tropical (STZ), North Temperate (NTZ) and South Temperate (STZ).

When the very thin, and low contrast Equatorial Belt can be seen, the Equatorial Zone splits into Equatorial Zone North (EZn) and South (EZs). (NOTE: When observers fail to distinguish between dark belts and light bands, they may misuse terminology by saying they saw as many as thirteen belts on the planet!)

This introduces an important aspect of Jupiterean observation. Although the thirteen belts and bandlike zones are more or less always present, there is considerable variation in contrast between them and their surroundings. Sometimes the SSTB (South-South Temperate Belt) is visible and sometimes not. Or perhaps only a short segment of the SSTB can be seen. For this reason, observers must be careful not to judge seeing conditions, eye or scope performance based on what can (or can not) be seen during any single observing session.

Jupiter is very much a living planet and is constantly changing...

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Fine Detail: Micro Features

When a particular scope and seeing conditions reveal the four main belts (NTB, NEB, SEB, STB) it may also be possible to see one main micro feature - The Great Red Spot (GRS). The GRS lies on the southern edge of the SEB and nests within a second micro feature - the GRS "Socket". The GRS and GRS Socket lead the eye to another interesting micro-feature: The splitting of the SEB into two darker "beltlets" and a brighter "bandlet". The two beltlets are typically referred to as South Equatorial Belt North (SEBn) and South Equatorial Belt South (SEBs). Meanwhile, the bright zone between them may be spoken of as the SEBz.

GRS, GRS Socket, SEBn, SEBz and SEBs are all semi-permanent features - even as they change in visual contrast. The SEBn and SEBs may actually disappear as different hemispheres of the planet rotate in and out of view. (Something that in Jupiter's case happens very quickly due to its 10 hour "day".) Meanwhile, the GRS has lost a great deal of contrast and color density over the past few years but still remains detectable with scopes of modest aperture (75mms).

NOTE: There is about a 50/50 chance of seeing the GRS during any given observation. Ahkana Peck's Java Jupiter program can be used to determine the general location of the GRS for any time/date and also help identify the four Galilean satellites plus transiting shadows.

There are a number of less permanent Jupiter micro-features that may be thought of as temporary disturbences in atmospheric conditions. They are usually short-lived (days, weeks, possibly months) and most challenge scope, eye and seeing conditions. Individual features of this type may receive special designations when confirmed. These include bright "ovals", dark "barges", and "festoons". Whereas festoons are seen as "whirling" incursions into the EZ, white ovals and barges typically - but not necessarily - are embedded within - or along - the SEB and NEB.

Susceptibility of ovals, barges, and festoons to visual observation is quite low. Barges are the easiest of the three to discern. White ovals, like barges, may project into the EZ but only that part of the oval that lies within the belt frontier is usually seen. Occasionally, a transiting Galilean satellite may be mistaken for a white oval - but continued observation soon clarifies the matter. It takes fine conditions, a good scope, and a practiced eye to make out all such micro-features. A high quality refractor (4 inches and larger) or long focal ratio reflectors and catadioptics (6 inches or larger) are generally the minimum scope sizes needed to detect such features with confidence. Festoons often require even larger apertures, and may be detected as "textures" within the EZ by smaller scopes.

By definition "textures" are difficult to pin down, and usually extend over a large region of the atmosphere. One good place to look for "textural mottling" is within the NPR, SPR, SEB, or EZ. Textures often show repeating patterns of alternation in color or intensity. Once some part of a texture can be singled out by the eye, it achieves a level of susceptibility that warrants ongoing study and documentation. Thus, a barge, or oval may become apparent where none was seen previously. Monitoring the progress of individual features as they rotate (and sometimes migrate) around the planet is extremely useful in determining how "active" the planet is at any given time.

Jupiter has been aptly named "the Amateur's Planet". One reason is that professional astronomers are unable to watch it constantly. High quality / low central obstruction scopes of 12 inches in aperture or more can reveal as much of the planet as any well-established earthbased observatory scope. Identification of new features when they first become visible can be a means to make contributions to the study of the planet. Precise measurements of when such features transit Jupiter's central meridian or first become visible near the planet's limb can add useful data about events going on in Jupiter's very lively atmosphere.

A first step to enjoying the planets diversity, and making useful contributions to the scientific community begins with linking what you see with what you know. A solid foundation in the planet's nomenclature makes for an excellent start!

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Labeled CCD Image of Jupiter (with Satellite Transit)

Hi All,

Jeff made a good description of the many things visible on Jupiter. My friend Andrea (Tasselli) also supports us with a Jupiter image made on the 14th of November with a MN-66 (6 inch Mak-Newt).

Cor Berrevoets

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Unlabeled Sketch of Jupiter

Hi All,

At Cor's encouragement I made the following sketch of Jupiter. It is illustrative of what may be seen on a good night (7+/10) stability, through a well-collimated scope (in this case 150mm MCT Argo). High magnifications were used (most detailed view 360x, drawing at 210 to simplify manual tracking). No colored filters were employed. South is up.

Please note that the numerous darkenings in the various belts and along the edge of the N/SEB were actually seen through the ep. This is also true of the one lightening (oval) seen embedded in the NEB bordering the NTZ.

Carpe Noctem,

jeff

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Fill in the Blanks!

Hey its test time! Mentally fill in the blanks, agree/disagree and/or circle the correct answer in the statements below:

1. Jupiter's equator is about __% smaller/larger than its cental meridian.

2. A really good scope can reveal 13 belts running in parallel across the planets atmosphere!

3. The Equatorial Zone of the planet can at times be seen to consist of one belt and two bands through a high quality 100mm telescope.

4. The NEB is often seen to split into an NEBn and and NEBs.

5. The GRS is now a light colored hollow found at the southern side of the SEB.

6. Barges can often be seen along the southern edge of the NEB and may extend into the EZ.

7. White Ovals may be found anywhere in the planets atmosphere but are less likely to be seen in the ___ and ___ where temperatures are very low and corriolus forces are at a minimum.

8. NNTB stands for "North North Thermal Belt".

9. Features that are on the very limit of visibility within the planet's atmosphere contribute to the planets _______ especially when there are many similar features to be seen over a large area.

10. The advent of modern space probes, plus access to the HST along with the historical increase in the number of observatories throughout the world means that amateurs can make no real contribution to research on the planet.

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What 9 of 10 seeing & Good Optics Makes Possible

Jupiter showed a stunning amount of detail. A broad dark reddish brown belt and many smaller belts. The Great Red Spot is pale and gray. Nevertheless, it was easily seen with detail inside of it. Dark little notches (festoons?) off of the dark reddish brown belt toward the equator...at least five. Dark short rods in that belt. On GRS end of planet, below the easily seen double belt which contains the GRS, there were two additional thin bands seen on the side of Jupiter opposite the GRS. On the GRS side (and below the GRS) these thin belts faded away into a grayish area directly under the GRS.

Ganymede showed definite size. Though actually smaller, it seemed as large as Uranus and seemed to have a better delineated disk. Perhaps this is due to the color of Uranus being bluish green and Ganymede being yellowish. Also, I fancied I saw detail...only a hint....ONLY a hint...in the upper left hand corner (the corner toward Jupiter and toward the upper side of Jupiter (the side not containing the GRS).

- Otto Piechowski

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And What Poorer Seeing & Good Optics Doesn't...

...

Then I switched over to Jupiter, Io had just dissappeared it seems (checking the events list ... bummer). And the GRS was also not around, so what was I left with on this planet. A nice rich-colour NEB and a SEB that showed at times (seeing-dominates) that it is actually split into two. Below the SEB the signs of two dimmer belts once more. Above the NEB the NTB was rather dark but not over the whole span, from the meridian eastwards (westwards ??) it was definitely darker. At the point where the NTB became gradually dimmer (easily visible still) the NEB had a large extended dark area on the N-edge. But seeing dominated my views, the moons were not showing any decent airy-disc effects but were bumping around.

Cor

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And Limitations Imposed by Aperture.

Hi All,

Cat woke me early (round 5:30am) this morning. Couldn't sleep. Washed a few leftover dishes and noticed the Moon through the skylight in the kitchen. Finished up and grabbed the 80mm out of the study.

Fine view of Jupiter at 120x. Again the STTB is very contrasty. One of the Galileans cast a perfect little dot of light running right across it. A second more diffuse "spot" preceded that. Two Galileans lay to the west but not especially near the planets limb. STB was not visible. SEB appeared slightly thin at the middle (the rift or split). NEB very dark and contrasty - but red color not apparent. (There were thin clouds.) NTB could be faintly detected. NNTB was visible as a darkish line just below the NPR (All Things Considered).

I was very pleased with the quality of the planets presentation. Typical of a 6/10 seeing stability sky through Argo. One new first for the 80mm was a dark barge embedded in the NEB. So micro-level features are possible even at such a small aperture.

Because of this ran the magnification up to about 200X (9mm Plossl plus shorty thread in barlow). Sharp edge focus was lost, but I could still see the transit shadow reasonably well. Threaded the shorty in to the 10mm Ultrascopic for about 160x. This gave a solid view and may prove to be my "goto" magnification when looking for micro-features.

...

Clear and Steady,

jeff

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