Chapter 2

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Astronomy & Astrophysics
Clifford Orwin

2.1 Patterns in the Sky What does the earth look like from earth? On clear and moonless night, assuming you are away from city light, more than 2000 stars can be seen to the naked eye along with Milky Way identified by the whitish band of light. Patterns of the stars at night have not noticeably changed over the past few thousand years Constellations: Constellation: a region of the sky with well-defined borders, and the patterns of stars help to locate the borders. Official names for constellations visible in the Northern Hemisphere can be traced back to the ancient civilizations of the Middle East. Southern Hemisphere constellations carry th names that originate from the 17 century European explorers. The Celestial Sphere: Stars appear to lie close to one another, but it is an illusion because we lack depth perception when looking into space. This happened to Greeks and they imagined the stars and constellations to like on a celestial sphere that surrounds earth. Earth is at the center of the celestial sphere. Why? Where we are as we look into space The celestial sphere is used to label four special points and circles. 1. North celestial pole point directly over the earths North Pole 2. South celestial pole point directly over earths south pole 3. Celestial Equator projection of earths equator into space 4. Ecliptic path sun follows as it appears to circle around the sphere once o each year. (since earth is on a tilt, ecliptic is on a 23.5 ) The Milky Way: Refer to page 28 for explanation of the Milky Way The Local Sky: Sky appears to take the shape of a dome. We can only see half of the celestial sphere from any particular moment or location, while the other is blocked by the ground.
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