22.2 The Earth-Moon-Sun 22.2 The Earth-Moon-Sun SystemSystem

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I. Motions of EarthI. Motions of Earth

A. A. Rotation (Spinning)Rotation (Spinning) 1. Causes: Day and Night1. Causes: Day and Night 2. 24 hours- Solar Day2. 24 hours- Solar Day

Sidereal DaySidereal Day1. Complete rotation with respect to a star other than 1. Complete rotation with respect to a star other than our sunour sun2. Time it takes for the other star to appear in the same 2. Time it takes for the other star to appear in the same location (23 hours 56 minutes 4 seconds)location (23 hours 56 minutes 4 seconds)

B. B. Revolution (Elliptical Orbit)Revolution (Elliptical Orbit)1. Perihelion- Closest to 1. Perihelion- Closest to sun- Jan 3sun- Jan 3rdrd 2. Aphelion-Farthest from 2. Aphelion-Farthest from sun- July 4sun- July 4thth

C.C. Precession: Slight movement of Earth’s Precession: Slight movement of Earth’s axis over a period of 26,000 yearsaxis over a period of 26,000 years

F. PrecessionF. Precession1. 1. Wobble of a topWobble of a top2. Now- Points toward Polaris (North Star)2. Now- Points toward Polaris (North Star)3. 13,000 years- Vega3. 13,000 years- Vega4. Affects Climate4. Affects Climate

E. Earth’s Axis and SeasonsE. Earth’s Axis and Seasons

1. Ecliptic: Apparent annual path 1. Ecliptic: Apparent annual path of the sun against the backdrop of of the sun against the backdrop of the celestial spherethe celestial sphere2. Plane of Ecliptic: Imaginary 2. Plane of Ecliptic: Imaginary plane that connects Earths’ orbit plane that connects Earths’ orbit with the celestial spherewith the celestial sphere3. Celestial Equator: Projection of 3. Celestial Equator: Projection of Earth’s equator onto the skyEarth’s equator onto the sky

4. Spring Equinox and Autumn Equinox:4. Spring Equinox and Autumn Equinox:Plot sun on celestial sphere over a year- Plot sun on celestial sphere over a year- path intersects equator at two points path intersects equator at two points

5. Summer Solstice: Sun appears 23.5 5. Summer Solstice: Sun appears 23.5 degrees north of celestial equator degrees north of celestial equator 6. Winter Solstice: Sun appears 23.5 6. Winter Solstice: Sun appears 23.5 degrees south of celestial equatordegrees south of celestial equator

The EclipticThe Ecliptic

G. G. Earth-Sun MotionEarth-Sun Motion1. The solar system speeds toward 1. The solar system speeds toward VegaVega2. Sun revolves around the Milky Way 2. Sun revolves around the Milky Way Galaxy (230 million years)Galaxy (230 million years)3. Milky Way Galaxy is approaching 3. Milky Way Galaxy is approaching the Andromeda Galaxythe Andromeda Galaxy

PrecessionPrecession

II. Motions of the Earth-Moon II. Motions of the Earth-Moon SystemSystem

A. Perigee: moon is closestA. Perigee: moon is closestB. Apogee: moon is farthestB. Apogee: moon is farthestC. Phases: Caused by how much of the moon is lit by the C. Phases: Caused by how much of the moon is lit by the

sunsunD. Lunar MotionsD. Lunar Motions

1. Cycle: 29.5 days (Synodic Month)1. Cycle: 29.5 days (Synodic Month)2. Sidereal Month: 27 1/3 days- true period2. Sidereal Month: 27 1/3 days- true period3. Takes two extra days to reach the point between the 3. Takes two extra days to reach the point between the sun and earth (starting position) that we seesun and earth (starting position) that we see4. Same side of moon always faces the earth4. Same side of moon always faces the earth

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Phases of the MoonPhases of the Moon

Lunar MotionsLunar Motions

III. EclipsesIII. Eclipses

A.A. Solar Eclipse: When the moon moves in Solar Eclipse: When the moon moves in a line directly between Earth and the a line directly between Earth and the sun, it casts a dark shadow on Earth.sun, it casts a dark shadow on Earth.

B.B. Lunar Eclipse: Moon passes through the Lunar Eclipse: Moon passes through the Earth Shadow.Earth Shadow.

C.C. During a new-moon or full-moon phase, During a new-moon or full-moon phase, the moon’s orbit must cross the plane of the moon’s orbit must cross the plane of the ecliptic for an eclipse to take place.the ecliptic for an eclipse to take place.

Solar EclipseSolar Eclipse

Lunar EclipseLunar Eclipse