Transcript 22.2 The Earth-Moon-Sun System

22.2 The Earth-Moon-Sun
System
Pages 622-627
I. Motions of Earth
A.
Rotation (Spinning)
1. Causes: Day and Night
2. 24 hours- Solar Day
Sidereal Day
1. Complete rotation with respect to a star other than
our sun
2. Time it takes for the other star to appear in the same
location (23 hours 56 minutes 4 seconds)
B.
Revolution (Elliptical Orbit)
1. Perihelion- Closest to
rd
sun- Jan 3
2. Aphelion-Farthest from
th
sun- July 4
C.
Precession: Slight movement of Earth’s
axis over a period of 26,000 years
F. Precession
1. Wobble of a top
2. Now- Points toward Polaris (North Star)
3. 13,000 years- Vega
4. Affects Climate
E. Earth’s Axis and Seasons
1. Ecliptic: Apparent annual path
of the sun against the backdrop of
the celestial sphere
2. Plane of Ecliptic: Imaginary
plane that connects Earths’ orbit
with the celestial sphere
3. Celestial Equator: Projection of
Earth’s equator onto the sky
4. Spring Equinox and Autumn Equinox:
Plot sun on celestial sphere over a yearpath intersects equator at two points
5. Summer Solstice: Sun appears 23.5
degrees north of celestial equator
6. Winter Solstice: Sun appears 23.5
degrees south of celestial equator
The Ecliptic
G. Earth-Sun
Motion
1. The solar system speeds toward
Vega
2. Sun revolves around the Milky Way
Galaxy (230 million years)
3. Milky Way Galaxy is approaching
the Andromeda Galaxy
Precession
II. Motions of the Earth-Moon
System
A. Perigee: moon is closest
B. Apogee: moon is farthest
C. Phases: Caused by how much of the moon is lit by the
sun
D. Lunar Motions
1. Cycle: 29.5 days (Synodic Month)
2. Sidereal Month: 27 1/3 days- true period
3. Takes two extra days to reach the point between the
sun and earth (starting position) that we see
4. Same side of moon always faces the earth
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Phases of the Moon
Lunar Motions
III. Eclipses
A.
B.
C.
Solar Eclipse: When the moon moves in
a line directly between Earth and the
sun, it casts a dark shadow on Earth.
Lunar Eclipse: Moon passes through the
Earth Shadow.
During a new-moon or full-moon phase,
the moon’s orbit must cross the plane of
the ecliptic for an eclipse to take place.
Solar Eclipse
Lunar Eclipse