Astronomy Lab – the Wanderers
Goal
The purpose of this activity is for you to learn how the planets appear in the sky and how their appearance changes over time.
You will make observations of the planets using the Stellarium Web program. With this program you can make observations in a few minutes that took ancient astronomers years and even centuries to make. Lucky you!
Complete the checklist below in order to set things up with Stellarium Web.
❑ Start by running Stellarium Web in a browser. Adjust your view so that you are looking directly toward the South horizon and zoomed out so that you can see the East point of the horizon on the left and the West point of the horizon on the right. You should be able to see the letters E, S, W across the horizon. Throughout this exercise it is best to keep the S at the bottom of the view!
❑ From the tool bar at the bottom set: Constellations on, Atmosphere off, Landscape off, Equatorial Grid on, and Deep Sky Objects off. Full Screen is a good option for this lab!
❑ From the View Settings menu at upper left set: Milky Way off, DSS off, Meridian off, and Ecliptic on.
❑ With the above settings you can now click on the time control and use the slider and/or click forward/backward by days to view the changing appearance of the planets moving among the stars. To focus on a single planet, it is convenient and helpful to click on it so that is marked by a “cross hairs symbol”, which makes it easier to follow.
❑ While viewing a particular planet, it may drift out of the field of view. When this happens, it is convenient and helpful to use the time slider control to bring it back into view.
Observations and Data
1. The Sun is
always found on the ecliptic. The Moon is always found near
the ecliptic. What can be said about the planets and the ecliptic?
2. Motion
from west to east through the stars is called prograde (or direct)
motion. Motion from east to west through the stars is called retrograde
motion. Does each planet do both types? Which type of motion
occurs most of the time?
3. If a planet passes by the Sun (or the Sun passes by the planet) it is called a conjunction. Does each planet undergo conjunction at some point? Fill in the column in the table yes or no.
4. Opposition of a planet means that it passes a point on the ecliptic that is exactly opposite the Sun. Does each planet undergo opposition at some point? Fill in the column yes or no.
5. a. Upon
reaching opposition a planet is moving prograde or retrograde? Is this always
true?
b. Which planets move retrograde during a conjunction? Do such planets move
retrograde at every conjunction?
Use these observations to fill in the column describing when retrograde occurs.
6. Elongation is the angular separation of a planet from the Sun. Determine the maximum elongation for each planet. Any and every planet that reaches opposition has maximum elongation 180°, but planets that do not reach opposition only get so far from the Sun. Use the difference in right ascension (Sun vs. planet) to estimate the maximum elongation. One hour of right ascension is equal to 15° and four minutes of right ascension is equal to 1°.
7. Synodic
period is the time for a planet to undergo a complete cycle of motion relative
to the Sun. Determine the approximate synodic period of each planet. The best
way to do this is to freeze the motion when a particular planet reaches
conjunction – note the date and year. Then go forward in time until the same
planet again reaches a conjunction, moving in the same direction, having
completed one cycle of its motion. Note the date and year. Determine the
approximate number of days between the two events.
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Planet |
Conjunction occurs? |
Opposition occurs? (yes or no) |
When does retrograde occur? (conj. or opp.) |
Maximum Elongation? |
Synodic Period (days) |
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Mercury |
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Venus |
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Mars |
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Jupiter |
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Saturn |
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