Test 1 Outline - ASTR101 Outline for Test I 1. How does...

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ASTR101 Outline for Test I 1. How does rotation and revolution affect what we observe in the sky? a. Rotation- spinning motion about an axis i. Earth rotates every 24 hours ii. Sun, moon, and stars appear to rise in the east and set in the west iii. For some locations circumpolar stars circle the celestial pole in 24 hrs. b. Revolution- orbital motion of one body around another i. Earth revolves around the sun in 365 ¼ days ii. Why do we see different constellations depending on the time of year? 1. Constellation vary with seasons because our night sky lies in different directions in space as we orbit the sun iii. Sun appears to move with respect to the stars over 1 year (through the constellations of the zodiac) 2. What causes seasons? a. Caused by tilt of earths axis i. Summer 1. Path is long and high, steeper angle, concentrated sunlight, more hours of daylight ii. Winter 1. Path is short and low, less concentrated, longer shadows b. Sun commonly reaches zenith in tropics (23.5 degrees N to 23.5 degrees S) c. Two hemispheres experience opposite seasons because the orientation of earths axis relative to the sun i. Northern hemisphere tipped towards Sun in June, away in December ii. Opposite for Southern hemisphere 3. Understanding the Moon a. Phases i. Phases from new to full: waxing ii. Phases from full to new: waning iii. Phases just before and after new moon: crescent 1. New moon occurs when moon is between sun and earth iv. Phases just before and after full moon: gibbous b. We always see the same face of the moon because the time moon rotates on its axis= time it takes to orbit earth synchronous rotation 4. Eclipses a. Occur when sun, moon and earth all fall into a straight line b. Moons orbit is slightly inclined (about 5 degrees) to plane of earths orbit around the sun ecliptic plane c. Eclipses occur about twice a year (when nodes line up between sun and earth)
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i. Lunar eclipse- occurs when Earth is directly between Sun and moon earths shadow falls on the moon (full moon at node) 1. Umbra is where the sunlight is completely blocked, a. If the moon passes through Earths umbra we see a total lunar eclipse b. If only part of the moon passes through Earths umbra we see a partial lunar eclipse c. If the moon passes only through earths penumbra we see a penumbral lunar eclipse (most common) ii. Solar eclipse- occurs when moon lies directly between sun and earth so Moons shadow falls on earth (new moon at node) a. If moon blocks full disk of sun you see a total solar eclipse (only if you are in the umbra, lasts minutes) b. People in penumbral shadow see a partial solar eclipse c. Solar eclipse may occur when Moon is far from Earths orbit, umbra does not reach surface, people directly behind umbra see annual solar eclipse 5. Geocentric and Heliocentric models a. Apparent retrograde motion: planets usually move eastward but occasionally reverse course moving westward rather than east (sun- centered system explains this) b. Greek did not want to abandon earth-centered model
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Test 1 Outline - ASTR101 Outline for Test I 1. How does...

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