ASTRONOMY 1021 October 5 , 2010
Astronomy – Lecture 4
Phases of the Moon & Eclipses…
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
o So at a latitude of 23.5 degrees.
o Cancer (north) and Capricorn (south) points on earth where sun is overhead at noon on
o At the time they were named, June occurred when sun was in Cancer, now the sun is in
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