LAB6

Orbits of the Planets Name: Objectives This exercise will help you visualize the relationship between the orbits of the planets in our solar system. You will observe the shapes of each planet's orbit, the different orbital periods in relation to one another, and the important positional alignments of the planets in relation to the Earth and Sun. Introduction The Ecliptic plane is the plane defined by the Earth's orbit about the Sun. It turns out that all of the planets' orbits lie within 7 ° of this plane. From the Earth view, the planets lie along the Ecliptic line (+/-). The positions of the planetary orbits, relative to the Earth's orbit, fall into two categories. These are the "Inferior" planets, whose orbits lie inside of the Earth's and the "Superior" planets, with orbits outside of the Earth's. This should not be confused with the terms "Inner/Terrestrial", for Mercury, Venus, Earth and Mars, and "Outer/Jovian" for Jupiter, Saturn, Uranus and Neptune. By now, you should know the order of the planets from the Sun outward as in Table 1: Solar System Physical Data Table 1. Name Equatorial Radii (km) [Earth] MASS (kg) [Earth] MEAN DENSITY (kg/m 3 ) Sun 6.96 X 10 5 [109.1] 1.99 X 10 30 [3.3 X 10 5 ] --- Mercury 2440 [0.38] 3.30 X 10 23 [0.055] 5430 Venus 6052 [0.95] 4.87 X 10 24 [0.82] 5240 Earth 6378 [1.00] 5.97 X 10 24 [1.00] 5520 Mars 3394 [0.53] 6.42 X 10 23 [0.11] 3930 Jupiter 71492 [11.21] 1.90 X 10 27 [317.8] 1330 Saturn 60268 [9.45] 5.68 X 10 26 [95.16] 690 Uranus 25559 [4.01] 8.68 X 10 25 [14.54] 1270 Neptune 24766 [3.88] 1.02 X 10 26 [17.15] 1640 1

Orbits of the Jovian Planets Figure 1. Orbits of the Jovian Planets Figure 2. Orbits of the Terrestrial Planets 2

Conjunctions  Inferior Conjunction is when the Inferior planet is in line with the Earth and Sun, and is located between the Earth and the Sun.  Superior Conjunction is when the Inferior planet is in line with the Earth and Sun, and is located on the opposite side of the Sun from the Earth. Figure 4. Inferior and Superior Conjunctions of Mercury G. Superior Planets 4

Figure 5. Oppositions and Conjunctions Opposition and Conjunction of Mars Step 1. A. Start Stellarium. It should be in the default configuration you setup in the Using Stellarium exercise. You should be viewing to your South and set the program to full screen. B. Bring up the Location Window and select your current location C. Bring up the Date/Time Window and set the time for 10:00:00 local time for today. Move the Date/Time Window to the upper right corner and leave it open. D. Set you view to the South with a Field Of View (FOV) of at least 100°. Use the mouse roll to adjust the field of view. Roll it forward to zoom in and outward to zoom out. E. Turn off the Ground and the Atmosphere. F. Open the Search window and type solar system observer and press search. G. Press “Ctrl” and then letter “G”. H. Open the Search window and type the sun. I. Open the Sky and viewing options window, and un-check the stars. Go to the second tab (SSO) and check show planets orbits, show planets orbits only, show orbit for selected planet, show planet trail, show trail only for selected planets, show planets markers, and move the slider of labels and markers all the way to the right 5

Step 3. A. Reset the date/time for today at 10:00:00. B. Now set the FOV until you can see Mars; and its orbit just fills the screen from top to bottom. C. Now advance the time in one day increments until you see at least one of the planets (Mercury, Venus or Mars) line up directly with an imaginary line through the Earth and Sun. D. Determine which type of conjunction or opposition is observed for any planets in alignment (Mercury, Venus and/or Mars). Record the date for that planet in the correct row corresponding to its current type of alignment. E. Continue until you have filled out all of Table 2 for Mercury, Venus and Mars. F. Reset the date/time for today at 10:00:00. G. With the Sun still selected and centered, zoom out until the orbit of Jupiter just fits in the screen from top to bottom. H. Now advance the time in one month increments until Jupiter is close to aligning directly with an imaginary line through the Earth and Sun. You may need to move the days back and forth to get a good approximation of the dates of alignment. I. Determine which type of conjunction or opposition is observed for Jupiter and record the date in the correct row corresponding to its current type of alignment. Conjunctions and Oppositions - Table 2. -Mercury- Year Month Day Inferior Conjunction Superior Conjunction -Venus- Year Month Day Inferior Conjunction Superior Conjunction -Mars- Year Month Day Conjunction Opposition -Jupiter- Year Month Day 7

Conjunction Opposition Step 4. A. Using the data in Table 1, answer the following:  Question 1: Which planet appears to have the most elliptical (non- circular) orbit? ______________  Question 2: Use your internet browser to look up the eccentricity of the terrestrial planets and Jupiter. Record your findings in the table 3 below. Table 3. Eccentricity of planets Planet Eccentricity Mercury Venus Earth Mars Jupiter  Compare your findings from question 1 to the data in the above table. Do they match? 8