Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS

1. Which of the following appears to move on the celestial sphere?
(a) Planets
(b) Stars
(c) Both "a" and "b"

Planets appear to move on the celestial sphere because they are close to us, but stars don't because they are so far away.

2. The Earth takes just over 365 days to orbit the sun. What is this time called?
(a) Rotational period
(b) Revolution period
(c) Circular period

The period an object takes to make one revolution around another object is the revolution period. The rotational period, on the other hand, is how long it takes an object to rotate on its axis.

3. If the moon rises just after the sun sets, what type of moon will it probably be?
(a) No moon
(b) Quarter moon
(c) Full moon

The moon and the sun rise in the east, and set in the west. If the moon rises right after the sun sets, it is likely to be lit by sunlight as a full moon.

4. How big is an astronomical unit?
(a) The semi-major axis of the Earth
(b) The semi-minor axis of the Earth
(c) The major axis of the Earth

An astronomical unit (AU) is the same as the semi-major axis of the Earth. An AU is about 150 million kilometers.

5. Do we travel at a constant speed on our orbit around the sun?
(a) Yes
(b) No
(c) Only when there are cops around

We don't travel at a constant speed on our orbit around the sun. The Earth's orbit is elliptical, not a perfect circle. Kepler's second law says that we move faster in our orbit the closer we are to the sun.

6. What is astronomy?
Astronomy is the organized study of the universe above the Earth's atmosphere.

7. Where is the celestial sphere?
The celestial sphere is in the mind of the beholder. It is an imaginary surface on which the stars and other heavenly bodies are plotted.

8. Why are stellar parallaxes so hard to measure?
Stellar parallaxes are small (less than one second of arc) and hard to measure because even nearby stars are so far from us…

9. As seen from the Earth, do stars appear to rise in the east or the west?
Because of the Earth's rotation, stars rise in the east, just like the Sun does.

10. How big is one AU?
One AU is the semi-major axis of the Earth's orbit around the Sun: 93 million miles or 150 million kilometers.

11. Whose carefully recorded positions of Mars and other planets were used by Kepler?
Tycho Brahe carefully recorded the positions of Mars and other planets without the benefit of a telescope.

12. Did Galileo invent the telescope?
No, but he perfected it and used it for the first time to record the appearance of the Sun, planets, and some of the planets' moons.

13. How did Galileo use the moons of Jupiter to argue for the Copernican view of a heliocentric universe?
He observed that the four largest moons of Jupiter revolve in the same direction and in the same plane around Jupiter from night to night, just like planets revolving around the Sun.

14. Why are Newton's laws considered more general and deeper than Kepler's laws?
Newton's laws are more universal than Kepler's laws, since they can be applied to the motion of any mass, be it baseballs, cars, rockets, or planets.

15. What's your favorite astronaut food?
Ours is frozen astronaut ice cream. It's sooooooo good that we need seven "o"s to say how good it is.

What's your favorite astronaut food? Email your responses to Astro Boy at astroboy@cerebellum.com.

  Click here to return to the Episode Page.