Planetary Observers Club Chair:

Aaron Clevenson
19411 Cluster Oaks Drive
Humble, TX 77346

E-mail: aaron@clevenson.org

The Projects for the Outer Solar System

 

JUPITER: The Great Red Spot

Jupiter is by far the easiest planet to observe. Its giant disk offers the most detail to the amateur observer. Even at its smallest it is 30 arc-seconds in diameter, and at opposition it can be almost 50 arc-seconds, twice the size of Mars even though Jupiter is ten times further away from us! You are to time the rotation of the Red Spot across the center of the disk of the planet Jupiter. In the "Calendar Notes" column in Sky and Telescope magazine the dates and times are given when this famous feature on Jupiter is due to cross the Central Meridian of the planet. The Central Meridian (CM) is a line drawn from the planet's north pole to its south pole dividing the great globe into two equal eastern and western sections. This project will require three timings. The first is the time at which the leading edge of the spot crosses the CM. The second is the time at which the spot appears centered exactly on the CM. The third is the time at which the trailing edge of the spot reached the CM. Use the S&T column to guide your observing sessions. If you can only make one timing, make it number two, the central transit time. Access to a WWV time signal is preferable but if this is impossible, the observation is still acceptable. State if WWV or another standard time source was used in making your report. Do not forget to convert to Universal Time. During the past few years the Great Red Spot has been very pale and should perhaps be known as the Great Pale Salmon Colored Spot!

JUPITER: The Galilean Satellites

Ever since Galileo it has been noted that the planet Jupiter and its four brightest and largest satellites form a kind of miniature solar system with a speeded up time scale. This magnification of time scale makes the system specially interesting to those who study potential changes in orbital mechanics. We have observing data on Jupiter's moons going back about 300 years. This consists of the recorded times when a satellite disappeared on entering Jupiter's shadow or reappeared upon exiting from it. Studying this data makes it possible to determine if Jupiter' satellite's orbits, and by inference, planetary orbits, change over periods of time. These eclipses are spectacular phenomena to watch in a small telescope. Since timings require a WWV time signal receiver. For this exercise we will only ask you to sketch the satellite positions on the this page for six consecutive nights identifying each satellite in your sketches. Include a copy of them in your report. As much as possible, try not to skip more that one night between consecutive viewings. The "Jupiter's Moons" chart in the Almanac section of astronomy magazines each month will help you to identify the individual moons.

 

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To show the East-West direction of your sketches show with an arrow the direction of drift in your field-of-view without a drive running.

 

JUPITER: The Cloud Belts

The first thing that comes to a person's attention when looking at the disk of the great planet Jupiter are the striated clouds of it's turbulent atmosphere. Fascinating and compelling, even a modest telescope reveals a good amount of detail, but always leaves you yearning for more. Through the years a system of nomenclature has been applied to the alternating dark and light areas called belts and zones, respectively. Coupled with the giants fast rate of spin (Jupiter's bulk rotates once in a little under ten hours) even the casual observer can notice something new. Below is a detailed list of the main cloud bands. Not all are always present all of the time. Jupiter's dynamics are too complicated for that. How many can you see? Make your own sketch and label those parts that seem to match up with the accompanying diagram. Include a copy of your sketch in your report.

Do not worry about a lot of detail. In fact Jupiter rotates so rapidly that features may move if you take too long to work on details. NOTE: Your telescope may show Jupiter inverted.

To show the East-West direction of your sketch show with an arrow the direction of drift in your field-of-view without a drive running.

 

JUPITER: Satellite Discovery

On January 7, 1610 Galileo Galilei observed the planet Jupiter with his fourth and latest telescope. He had "spared no time and expense" in its production. With it he saw three small bright stars near the bright planet and assumed that they were fixed background stars. The next night he observed the Jovian planet again and was amazed to discover that the "stars" had changed their positions relative to the planet's disk. Very perplexing! Within a week he had seen all four of what we now call the Galileian satellites of Jupiter.

Galileo was using a primitive simple telescope magnifying about twenty times. Can you duplicate his feat with the modern lenses of a pair of binoculars?

It is important that the binoculars be held perfectly steady for the eye to pick out the tiny moons next to Jupiter's glare. Any movement, even the blood pumping through your veins will make them difficult to see. Try bracing your binoculars against a solid structure like a telephone pole or the roof of a car. Better yet, mount them on a tripod. Observe the satellites for several days and then describle your experience.

 

JUPITER: Satellite Shadow Transits

Shadow transits occur quite often and are a phenomenon that can easily be seen by the amateur. The shadows cast by the Galilean satellites are seen as tiny black dots slowly proceeding across the cloud tops of the giant planet.

Your task is to determine which of the four largest Jovian moons is casting the shadow. First you need to know if Jupiter is approaching its yearly opposition or if opposition has already passed. If Jupiter is moving toward its opposition then the shadow precedes the satellite. The moon's shadow will fall on the planet while the moon itself is still nearing the planet's limb. If opposition has passed, the moon will cross the planet's disc first, followed by its shadow. By consulting a Galilean Satellite Chart in an astronomy periodical you should be able to determine which satellite is casting the shadow. Which satellite was it?

 

JUPITER: Satellite Transits

Watching the Galilean Moons transit the disk of Jupiter is considerably more of a challenge than watching their corresponding shadows. The tiny little disks are similar in color to their parent planet so the satellite quickly gets lost from view in its frontal passage. The satellites can often be seen under the right conditions with larger apertures, for a few minutes, while still on the edge of Jupiter's limb. The limb tends to be slightly darker than the face of the planet itself. The contrast between the two helps the satellite to show up. The slow ingress or egress varies with each satellite. Io and Europa, being inner satellites, take only about two and a half minutes to ease onto or off of Jupiter's limb. Ganymede moves much more slowly, taking seven minutes, and Callisto crawls across the limb for nine minutes. If you are able to detect these ingresses or egresses, time them with a stop watch and compare the times with those just given. An alternative project would be to time the ingress or egress of one of the satellites into or out of Jupiter's shadow. What satellite did you time?

 

JUPITER: Satellite Occultations/Eclipses

Occultations of the Galileon satellites as they pass behind the limb or eclipses as they move into the shadow of the giant planet are much easier to see than transits. Your task is to time the disappearance or reappearance of one of these satellites by using a radio tuned to the WWV National Time Standards signal out of Ft. Collins, Colorado. Then compare it to the time printed in the astronomy periodicals. Note the time the moment the satellite completely disappears or reappears behind Jupiter's limb or shadow. Timing a reappearance is much more difficult since the you do not know precisely when or where it will reappear. What satellite did you time?

 

SATURN: The Rings

Saturn is the most impressive object in the solar system and surely one of the most beautiful. Saturn is the only ringed planet whose rings are visible in the amateur's telescope. On a clear steady night, nothing rivals the sharp divisions and contrast seen in Saturn's ring system. Because of Saturn's considerable distance, high powers must be used. Under average conditions use a power of about 40X per inch of telescope aperture. However, do not sacrifice a clear image for the sake of a larger one. Make a sketch of what you see. Using a pre-drawn outline for your drawing can save a lot of time and effort at the eyepiece. The "Planetary Data" section of the astronomy magazines is an excellent resource for this. Place an arrow on your drawing to indicate the direction of drift when your scope is not tracking. Include a copy of your sketch in your report.

 

OBSERVATIONAL NOTES

 

 

1. The day/month/year/time________________________________________

2. The seeing conditions___________________________________________

3. The aperture of the telescope._____________________________________

4. The focal length of the telescope.___________________________________

5. The focal length of your telescopes eyepiece.__________________________

6. Your own observational comments and impressions.____________________

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Sketch of Saturn

 

 

SATURN: The Cassini Division

Within the three major rings that can be seen through the amateur telescope is the prominent gap known as the Cassini Division. It separates the "B" Ring, the brightest ring, from the "A" Ring and appears as a fine black line circling the planet. It is most easily seen on the two protrusions of the rings on either side of the planet known as ansae.

The axial telt of Saturn and the inclination of Saturn's orbit compared with the Earth's, combine to cause the

plane of Saturn's rings to change their tilt. About every 7.25 years the rings go from edge-on to fully open. Your ability to see the Cassini Division will vary depending on how "open" or "edge-on" the rings are. Seeing and aperture size will also affect your ability.

Describe your view of Cassini's Division. Can you see it? Can you barely see it or does it "jump out at you?" How complete a circle of the rings can you detect?

 

SATURN: Disk Markings

At first glance the face of Saturn's disk seems rather boring, a bland creamy-yellow ball. Less than half the apparent diameter of Jupiter with proportionately duller markings, Saturn requires diligent study and a tranquil night of seeing. The greater your observing skill or equipment, the more subtle are the details you will see.

You should be able to tell that one hemisphere is decidedly darker than the other Can you tell which one? Be certain you know if your telescope shows an upright or an inverted image. Belts, zones and spots similar to Jupiter's can sometimes be glimpsed through the planet's top layer of obscuring haze. They are subtle. What do you see? Record your impressions.

 

SATURN: The Satellites

Of all the satellites of Saturn, only six of them can be seen in telescopes with moderate sized apertures. How many can you spot?

	Magnitude	Orbital Period (Earth Days)	Recommended Aperture
Enceladus	11.8	1.37	8-inch
Tethys	10.3	1.9	6-inch
Dione	10.4	2.7	6-inch
Rhea	9.7	4.5	3-inch
Titan	8.4	15.9	2-inch
Iapetus	10.2-11.9 (varies)	79.3	8-inch

How many satellites you will be able to see will depend a great deal on atmospheric conditions . For example, I have seen all of them in a six-inch. In contrast with Jupiter, where all four moons orbital plane is nearly a straight line from Earth's viewpoint, Saturn's equatorial plane is considerably more tilted. This means that the orbits of the satellites can vary from a nearly straight line configuration to that of nearly a 30° ellipse depending on where Saturn and Earth are located in their orbits. This inclination changes at about a 15 year interval. Finder charts can be found in astronomy periodicals that will help you determine which of the Saturnian satellites you are seeing.

A note on Iapetus. The magnitude variation can be explained by the fact that it has two vastly different hemispheres. One reflects light almost two magnitudes brighter than the other. What satellites did you see?

 

URANUS: Locating

In 1781 the first non-classical planet was discovered by amateur astronomer William Herschel. The discovery changed Herschel's life forever and was a blow to astrologers who by their "craft" had no inkling that a seventh planet existed. Actually the planet had been seen and charted years before on no fewer than seventeen different occasions. Uranus is visible to the dark adapted naked eye under good skies. But the astronomers simply added it to their charts just like any other sixth magnitude star. It was Herschel who finally had enough resolving power and the observer's eye who could tell it had, in fact, a tiny disk, and was not a simple star-like point. He first suspected the tiny object to be a distant comet and took a series of measurements of its position. It was somewhat later that he realized its true nature.

It is much easier today for you and I. The 3.8 arc-second greenish disk shines at a magnitude of 5.7 and can be readily found using locator charts published in the astronomical periodicals. Give a verbal description your eyepiece impression.

 

NEPTUNE: Identifying

Although similar in size and appearance as Uranus, Neptune's distance averages over one billion miles further from the Earth. This great distance makes it's apparent diameter about 2-1/2 arc-seconds, a little over half the size of Uranus.

The 7.6th magnitude bluish dot will probably look stellar, for its tiny disk is near the resolving limit of most amateur telescopes. Consult your favorite astronomy periodical to find out where it is currently located. Write a verbal description of your impression.