Section I: Answer the following Questions using any source (textbooks, Google, Wikipedia, NASA etc.):

1. How does the Moon move with respect to the stars?

2. How does the fact that we always see one side of the Moon prove that the Moon rotates once every orbital period?

3. In a particular year the Moon is in the constellation Aries on June 1st. What date will it be in Aries the next time?

4. Why does the Moon have phases?

5. Why are New Moon phases longer than a sidereal period (27.3 days) apart from each other?

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6. If the Moon was full 7 nights ago, what time of day (night) should you look for the Moon to be up high in the sky in the south today? Explain your answer.

Lunar Phase Simulator.

7. What are the real angular separations for New and Gibbous phase?

8. About how much difference in time is there between moonset and sunset at first quarter phase? Does the Moon set before or after the Sun at that phase?

9. About how much difference in time is there between moonset and sunset at new phase?

10. About when will the Waxing Crescent Moon be on the meridian? Explain your answer.

11. The Moon is low in the western sky at sunrise, what is its phase? Explain!

Refer to the figure from the Rotating Sky Module Paths of Stars.

12. Why do we not have eclipses every month?

13. How do the planets move with respect to the stars?

14. Why are Venus, and Mercury never seen at midnight while the other planets can be visible then?

15. What phase would Venus be in when it is almost directly between us and the Sun? Where would it be in its orbit if we see in a gibbous phase?

See the figure.

Section II: answer the following questions based on Observation Module:

1. Read the module:

Basic Observations

What We See

Man has looked up at the skies for countless ages. But many are not simply content to admire its majesty but yearn to understand it. To help us understand the heavens, we create models representations, which while simplified but retain many key elements. It is through models that astronomers understand most phenomena from stars to galaxies to the universe as a whole. Weve been doing it a long time but the basic process of modeling remains the same: observe and describe those observations as part of the model.

What are some of the astronomical observations that we see?

• All objects in the heavens rise in the east and set in the west.
• The sun travels around the sky in 24 hours.
• The stars travel around the sky slightly faster than the sun (23 hours and 56 minutes). There are several thousand stars that we can see at night with good visibility.

There are many ways to describe these events. For example, we could say that a bright luminous god pulling a chariot with a vast drapery of stars flies through the heavens in a great circle, creating day and night. But that wouldnt be very satisfactory to us. Nor was it satisfactory to the ancient Greek philosophers.

The Round Earth

To model the heavens, we need a model of the earth. Many in the ancient world believed that it was round. Some of the earliest records come from Ancient Greece (though other cultures were aware of the earths sphericity). The Pythagoreans and Plato for example taught that the earth was round.

Aristotle recorded several observations arguing for a round earth including:

• The lower part of a ship disappears below the horizon first.
• Different stars are visible to different observers and the path they take is different. This implies that up is in a different direction as would be the case for those on a spherical surface.
• The shadows of the earth on the moon during a lunar eclipse are consistent with the earth being a sphere.

Several ancient Greeks even measured the radius of the earth. Eratosthenes is perhaps the most famous. Due to a serendipitous cancellation of errors, he came up with a value that was extremely close to the accepted value of the earths circumference of 24,900 miles. Other Greeks used more sophisticated and correct methods and got significantly smaller values (which incidentally led Christopher Columbus to believe that he could successfully traverse West across the Atlantic to Asia).

The Planets

The sun and stars all moved across the sky in a regular, predictable way. The stars moved slightly faster than the sun (by about 4 minutes/day or equivalently 1/day). The planets, Mercury, Venus, Mars, Jupiter, and Saturn, however behaved differently. The following observations applied to them:

• Mercury and Venus were only seen near sunrise or sunset.
• Mars, Jupiter, and Saturn usually moved slower than the stars (prograde motion) Sometimes Mars, Jupiter, and Saturn moved faster than the stars (retrograde motion Retrograde motion varied slightly in when and how long it would last.

It is precisely this reason that the planets have their name, which in Greek means wanderers. The challenge was how to observe them. Plato is reported to have put forth the challenge to do so with simple, uniform circular motion.

1. Answer the following questions
2. List the three pieces of evidence that the Ancient Greek Astronomers/Philosophers used to assert that the Earth was a sphere.

1. What is retrograde motion?

iii. What does the Greek word planet translate into English as?