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Astronomy Lecture 04 - Oct 5.docx

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Western University
Astronomy 1021
Jan Cami

th ASTRONOMY 1021 October 5 , 2010 Astronomy – Lecture 4 Phases of the Moon & Eclipses… Precession: o Polaris won’t be north forever o Constellations where the Sun is at equinox and solstices will change over time o Tropic of Cancer and Tropic of Capricorn: points where Sun directly overhead at noon at summer solstice o So at a latitude of 23.5 degrees. Tropics: o Cancer (north) and Capricorn (south) points on earth where sun is overhead at noon on solstice o At the time they were named, June occurred when sun was in Cancer, now the sun is in Taurus. Moon Goals: o Demonstrate how and why the moon shows different phases o Tell the time of day/night from the position and phase of the moon and vice versa o Explain conditions required for different types of lunar and solar eclipses. o Distinguish between different types of eclipses (partial, total and annular) The Moon Phases: o We cannot see entire surface at all times o See only what is illuminated by sun o Half of the moon’s surface at all times o Relation between phase of the moon and the time and direction we see the moon. o Full moon always rises in the East at sunset, while a first quarter moon will always be in the South at sunset. o Moon resides on celestial sphere, therefore diurnal motions due to Earth’s rotation. o Additionally, the Moon orbits the Earth, and therefore its position with respect to the background stars change over longer time scales, slower than the diurnal motions. o ORBIT: 27.3 days counter-clockwise from North Pole. Therefore it moves eastward through the constellations at 360 degrees / 27.3 days, about 13 degrees a day, more than 0.5 degrees an hour. o Orbit of the Moon nearly follows ecliptic, not equator so it’s tilted! o Phase we see depends on Moon’s position relative to Sun. But location in sky also depends on the Moon’s position relative to the Sun. o (look at slides for diagrams and crap that I keep missing) o New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Third Quarter, Waning Crescent th ASTRONOMY 1021
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