Download Ellipses, Parallax, and Retrograde Motion

Astronomy
2012
Name ___________________________
Ellipses, Parallax, and Retrograde Motion – Study Guide
Parallax
1. The farther an object is from the observer, the __________ the parallax.
2. T or F Parallax is an apparent motion. (appears to the observer only)
3. The smaller the baseline of the observer, the ___________ the parallax.
4. T or F
It is impossible to measure parallax with your unaided eye.
5. T or F
If a star has a parallax angle of 0.2, it is 5 parsecs distant.
6. T or F One parsec equals 3.26 light years.
7. The largest baseline astronomers use today is about equal to ________ .
a. the diameter of Earth
b. Earth—Moon distance
c. 2 AU’s
d. 1 AU
Ellipses
8. The greater the eccentricity, the more _________ the ellipse. Circular or oval?
9. Kepler’s 1st Law: All planets orbit in ____________(shape).
10. Kepler’s 2nd Law: The closer a planet is to the sun, the _________ it moves.
11. Kepler’s 3rd Law: The closer a planet is to the sun, the _________ its year is.
12. The Sun is at one ________ of the elliptical orbit.
Retrograde Motion
13. T or F All planets as observed from Earth will exhibit retrograde motion at some time.
14. T or F There are only two inferior planets in our Solar System.
15. T or F Retrograde motion is an apparent motion.
16. T or F Mars is brightest in our night sky when it is seen during retrograde cycle.
17. T or F Only superior planets can be in opposition with Earth.
18. T or F Any two celestial objects may appear in conjunction.
19. T or F The closer a planet is to the Sun, the faster it moves in its orbit.
20. T or F The more distant a planet, the longer it will appear in retrograde motion.
21. T or F All celestial objects will appear to move Eastward over a year’s time.
22. T or F During retrograde motion, an object appears to move westward over time.
23. T or F An example of opposition is when Mars appears directly overhead at midnight.
24. T or F When two objects are in conjunction, they are not actually very close together.
25. T or F Mercury and Venus do not ever appear very far away from the Sun.
Key Concepts/Possible Essay Questions
1. Why did the ancient astronomers not see parallax? What did they conclude?
2. How can you determine the latitude of Anchorage (or any place on Earth) using just your
hands and a clear night sky?
3. Discuss the difference between what we see (apparent) and what is real (actual) with
relation to retrograde motion or parallax.
4. Draw or describe a shape with an eccentricity of 0 (zero), 1 (one), 0.2 and 0.9. Include
where the foci (or center) are.
5. If the Earth still had a 23.5 tilt, but orbited the sun with an eccentricity of 0.8, how would
the length of our seasons change?
6. What causes retrograde motion? Do all planets appear to have retrograde motion?
7. How is parallax like retrograde motion? Hint: see question 3 above.
Make a system (sun-earth-planet) diagram that shows:
A. A planet at opposition with Earth.
B. A planet in conjunction with Jupiter.
C. A planet’s path during pro-grade and retrograde motion (label each portion, include E and W)
Draw a picture that defines:
A. Rotation
B. Revolution
C. retrograde motion
D. parallax
BONUS QUESTION(S) Only one or two will appear on the test. Answers ON LINE only
1. What does eccentricity of Earth look like?
2. Which planets are visible in our early morning sky (around 6 AM) this month?
3. Who explained retrograde motion by saying planets orbit in epicycles?
4. How many light years is a parsec?