Jupiter – the King of the Planets – presents more detail in a small telescope than any object but the Moon. Jupiter has light and dark bands running around the planet. The light-colored bands are called zones. They are where warm gas is rising high in the atmosphere. The darker-colored bands are called belts. They are where cool gas is sinking into the atmosphere. Within the belts and zones are many ovals and spots, which are storms in the planet’s atmosphere. The most famous and obvious spot is the Great Red Spot. The Great Red Spot can be seen on the south edge of the belt just south of Jupiter’s equator, but only when that side of Jupiter is facing us. Jupiter also has a complex system of moons, four of which can be seen in small telescopes. The four “Galilean Moons” discovered by Galileo are an obvious sight lined up in a row straddling the planet. From closest to furthest from Jupiter, these moons are Io, Europa, Ganymede and Callisto. (“I Eat Green Cheese,” can help you remember the order.) Jupiter does have a ring system, but it is not visible in small telescopes.
You will want to observe Jupiter with your mid-power (20-mm) eyepiece in order to see the moons, and then go to your high-power (10-mm) eyepiece to see detail on the planet. Note: If the atmosphere is particularly turbulent, you may want to stick with the 20-mm eyepiece so you don’t magnify the “mush.”
To observe the moons, you will use the space on the observing form which shows a small image of the planet. You should mark the position of any star-like objects you see in the eyepiece, trying to put them at a distance from the image on the paper that corresponds to their distance from the planet. You will need to judge this by eye; the best way is to try to judge how many planet diameters the nearest objects are, then you can space the more distant ones. Remember to use a pencil. It will be important to focus carefully. Make sure you indicate which directions are N, S, E & W. (Remember that if you turn off the clock drive, objects in the field of view drift toward the west.) Mark the positions of any star-like objects you see in the field with Jupiter. Jupiter is far enough away that its moons look like stars (although you may be able to notice the Galilean moons look like disks at high powers under a steady sky). After you make your sketch and return inside you may be able to identify which moons you saw.
For the planet itself, switch to high power and carefully focus. Take your time looking at the planet, waiting for moments when the atmosphere is steady and you can see more detail. As you notice features on Jupiter, sketch them on the observing form. Both you and your partner should make sketches from what you see at the eyepiece—you should both be observing—but you can compare notes about what you see. Look for subtle features on the planet’s disk. How many belts can you see? What colors do you see, and how do the width and darkness of the different belts compare? Sketch any ovals, spots or swirls that are visible. Make sure you indicate N, S, E & W on your sketch.
Procedure
· Polar align your mount and carefully align your finderscope. It will be difficult to locate Jupiter in the main telescope if your finderscope is not lined up with the telescope.
· On your observing form, make note of the time, conditions, equipment used, etc.
· Find Jupiter in your 30-mm eyepiece, then focus on it with your 20-mm eyepiece. Using the observing form and a pencil, make a sketch of all the star-like objects you see. Try to place them the correct distance from the planet, starting with the ones closest to Jupiter.
· Switch to your 10-mm eyepiece and focus carefully. If the image is mushy due to excessive atmospheric turbulence, you may want to go back to the 20-mm eyepiece.
· Using your observing form, carefully sketch the detail you see on the planet. Take you time and wait for moments of good seeing. Look for details in the belts and zones—in coloration, brightness, and structure. Compare notes with your partner as you take turns at the eyepiece and make your sketches.
· Once you are satisfied you have teased the last bit of detail out of your view and placed it on your sketch, return you equipment to the garage and return inside.
· Use the image on the overhead to identify any moons you saw.
· Include the sketches on your form as part of your lab report due next week.
Questions
1. Give two (2) reasons why you can expect to see more detail on Jupiter than on Saturn.
2. Sometimes not all 4 of the Galilean moons are visible around Jupiter (even when conditions are such that objects that bright are visible). What could cause a moon to not be visible? (Remember they orbit Jupiter.)