Jupiter
Goals of the Lab
To identify and observe the moons of Jupiter and their movements;
To identify and observe the features of Jupiter through careful observation.
Required Equipment: the telescope, a calculator, a watch, a stopwatch or watch with a second hand, and several printouts of the Observation Templates (the large version or the small version. You will also need to print out The Method of Transit Times. You will want to have read the help file on Angular Distances.
Background: Jupiter is the largest planet in the solar system and the second brightest nighttime object in the sky after Venus. Its mass is 318 times greater than the Earth's. From its mass and volume, one can calculate its density to be 1.3 grams per centimeter squared, not much greater than the density of water. Jupiter's low density is related to the fact that it is a gaseous planet, composed primarily of the light elements hydrogen and helium. Jupiter's composition is more similar to the sun and stars than to the earth. As a result, the surface of Jupiter is not solid. Instead, the atmosphere becomes thicker and denser at greater depths. The outer layers of the atmosphere are cold enough for ammonia, ammonium hydrosulfide, and water to condense into clouds. Jupiter's distinguishing colors are somewhat of a mystery to scientists. The ammonia clouds formed at high altitude are white, as expected. However, the lower clouds of ammonium hydrosulfide are also expected to be white; but reds, tans and browns are observed. Some sulfur or phosphorus compounds (we are not sure yet) add coloration to these white clouds.
The famous great red spot of Jupiter is an enormous hurricane system more than twice as wide as the Earth. The great red spot has endured since its discovery 350 years ago. The "red" color of the spot is actually quite subtle. The intensity of its color has changed with time and it has been very pale for more than a decade. The red spot is usually identifiable as an oval, white area surrounded by a darker outline. Jupiter's rotation carries the spot to the back side once every rotation, making it not always visible from earth.
When Galileo aimed his telescope at Jupiter in 1610, he noticed it had four companions or moons. These are the four brightest (and by far the largest) satellites of Jupiter and are known as the Galilean moons. In order of increasing distance from Jupiter, the Galilean moons are: Io, Europa, Ganymede and Callisto. They are roughly the same size as our Moon and each appears quite unique. Jupiter has dozens of other satellites; none are nearly as large as the Galilean moons.
NASA has explored Jupiter through the Voyager I and Voyager II missions (in 1979 and 1981) and in the 1990s through the Galileo mission. For the latest information and cool pictures, consult the Galileo spacecraft home page.
Part I: The Moons of Jupiter
Find Jupiter using the 25mm eyepiece. You should be able to see Jupiter and as many as four moons. Once you find Jupiter, pan the telescope east and west, moving Jupiter to either side of the field of view, to ensure you've seen all the moons.
Draw the 25 mm eyepiece field of view on an observation template. Include Jupiter and all moons, as well as any stars in the field of view. Draw the positions of the moons as accurately as possible.
Repeat step 2 four more times during the night, with each drawing separated by half an hour. You will need to come back during your work in Part II (below) to complete this. The repetition of this step will allow you to see the movement of Jupiter's moons.
Use the Method of Transit Times to measure the angular separation between the center of Jupiter and the moon which is closest to it. To determine this angular separation, you will use the same principle as the Method of Transit times. In this case, you want the distance between the center of Jupiter and its closest moon.
If Jupiter is to the West of the closest moon: use the fine adjust knobs to position the center of Jupiter at the edge of the field of view, i.e. half of Jupiter appears in your field of view. Turn off the drive, and measure the time it takes the closest moon to hit the edge of your field of view.
If Jupiter is to the East of the closest moon: use the fine adjust knobs to position the moon right at the edge of your field of view. Turn off the drive, and measure the time it takes for the center of Jupiter to leave the field of view, i.e. the time until Jupiter is just half visible.
Report the time you measured (in seconds). You will use this data in Part III to calculate the physical distance between Jupiter and this moon.
Note: All observations should contain the directions N/S and E/W, the time, the date, and the weather conditions.
Part II: Jupiter
Suggestion: Take your time with this part of the lab. It is often difficult at first to see planetary details in the telescope. The inevitable shaking of the field of view of the telescope from the parking garage adds to the difficulty. Patiently study the image of Jupiter in the eyepiece.
Begin with Jupiter centered in the 25mm eyepiece. Once Jupiter is centered, switch to the 10mm eyepiece. Focus the image of Jupiter well.
Sketch Jupiter, as well as the entire field of view, on a large observation template. Include all noticeable details about the planet. You should be able to see two east-west bands. Use the following questions to help you look for harder-to-see features. You may not be able see all of the features listed, just draw the features you are able to see. Address the following questions, as well as drawing additional features.
Comment on how dark the two most prominent east-west bands appear to be? Is one darker than the other? Is one wider than the other?
Do the bands appear uniform or "clumpy"? Are some spots on the bands darker/lighter than the rest of the band?
Are there any additional east-west bands which appear darker or lighter than the rest of Jupiter?
Comment on noticeable differences between the north and south poles and the rest of Jupiter. Do you notice any differences in color?
Can you see any features oriented north-south?
Comment on the coloring at the limbs (edges) of Jupiter. Note any colors you see, and where do you see them.
Can you see the Great Red Spot? In recent years it has been very pale, and it is not always facing us. If you can see the Spot, indicate its location on your sketch, and describe its appearance.
Can you see any moons in the 10mm field of view? If yes, locate them on your sketch.
Describe Jupiter's shape. Does it appear perfectly circular, or is it squashed in one direction? Is it wider east-west or north-south? How apparent is this, if you can see it at all?
Measure the angular diameter of Jupiter using the Method of Transit Times. Report your observations (the time of the transit). You will use this time in the next section to calculate the diameter of Jupiter in kilometers.
Part III: Questions and Calculations
From the observations you made repeatedly in part I.3., did any of the moons of Jupiter move? Using what you observed, comment qualitatively on how the period Jupiter's closest moons compare to the period of Earth's moon (approximately a month).
Jupiter is between 4 and 6 AU away from the Earth. Typically when it is visible in lab, it will be roughly 4.5 AU (=6.7×108 km) away. Covert your time to arcseconds and then to radians using the conversions in the Method of Transit Times. Then, calculate the physical diameter of Jupiter in kilometers (km) using the small angle formula:
a (in radians) = h / dwhere a is the angular diameter in radians, h is the physical diameter of Jupiter, and d is the distance to Jupiter.
How does the diameter of Jupiter compare with Earth's diameter (13,000 km)? In other words, what is the ratio of Jupiter's diameter relative to that of Earth? How does Jupiter's diameter compare with the average Earth-Moon distance (384,000 km)?
Using the same method used in question 2 of Part III, calculate the projected physical distance between Jupiter and the closest moon. In this case, use the time you measured in question 5 of Part I. Use the small angle formula (above), only now d is the projected distance. How does this compare to the average Earth-Moon distance?