PHY 111

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8/29/2011

PHS 111

Chapter 1

1.      (1.1) What is the celestial sphere? What are the celestial equator and the ecliptic?

The celestial sphere has no physical reality, but serves as a model a way of simplifying the arrangement and motions of celestial bodies so they are easier to visualize. The celestial equator is a sky marker used by astronomers. The ecliptic is the line that the Sun traces across the celestial sphere.

2.      (1.1) What is a constellation, and what is special about the zodiac constellations?

 A constellation is a fixed patterns on the celestial sphere formed by stars. The zodiac is 12 constellations that the ecliptic passes through.

3.      (1.2) What causes the seasons? The seasons are casued by the rotation axis it runs from the North Pole to the South Pole it is not perpendicular its tipped by 23.5 degrees. Some times of the year the Northern Hemisphere is pointed closer or farther from the Sun. The Northern and Southern Hemisphere have opposite seasons.

4.      (1.3) How long does it take the Moon to go through a cycle of phases? The cycles of phases lasts approximately 29.5 days.

5.      (1.3) How much later does the Moon rise each day? The Moon rises about 50 minutes later each night.

Chapter 2

1.      (2.1) What is meant by the phrase angular diameter?  It is an angle that you take on one edge and then the opposite end and when the distance is also known it can be used to calculate a bodies true diameter.

2.      (2.1) If you triple your distance from an object, what happens to its angular size?  The objects size should shrink by a third.

3.      (2.1) What is parallax and how is it measured?  Parallax is a shift in a star’s apparent position resulting from Earth’s motion. It is measured using a powerful telescope because it is too small to be detected by the naked-eye because the stars were so enormously far away.

4.      (2.2) If you see a bright “star” in the sky, how could you tell whether it is a star or instead, for example, Venus?  The motions of the planets relative to the stars are very slow, detectable only through observations over many nights. The motion of the planets through the zodiac can be seen by marking off the postion of a planet on the celestial sphere over a period of a week or more.

5.      (2.2) Where on the celestial sphere would you look for the planets?  You would always look close to the ecliptic within the constellations of the zodiac.