Lecture 3 Phases of the Moon. Moon. Phases of the Moon. The Moon orbits the Earth ~ every month. The Moon appears to have different phases because we see more or less of the lighted side of the Moon depending on where it is with respect to the Sun. First Quarter. Waxing Gibbous. Waxing
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Phases of the Moon • The Moon orbits the Earth ~ every month. • The Moon appears to have different phases because we see more or less of the lighted side of the Moon depending on where it is with respect to the Sun.
First Quarter Waxing Gibbous Waxing Crescent Full Moon New Moon Waning Gibbous Waning Crescent Last Quarter Phases of the Moon
Rotation of the Moon • We only see one side of the moon • Moon rotates at the same rate as it orbits the Earth • When spin and orbital periods are correlated = synchronous orbit
Orbit of the Moon – Lunar Month • Sidereal Month = amount of time for the moon to come to same spot with respect to the celestial sphere. (27.3 days) • Solar Month = amount of time for the moon to come to same position with respect to the sun (29.5 days) • One Lunar phase cycle
Umbra Sun E Penumbra Eclipses • Umbra = darkest shadow of and object. • Sun completely blocked in umbra • Penumbra = lighter shadow • Sun only partially blocked
Eclipses • Solar eclipse = when the Earth passes through the shadow of the moon • Lunar eclipse = when the Moon passes through the shadow of the Earth
Umbra View from the Earth Sun E Penumbra Total Solar Eclipse • Sun completely covered by the moon -- seen only in the umbra
Umbra View from the Earth Sun E Penumbra Partial Solar Eclipse • Partial Eclipse: Part of Sun is blocked by the Moon -- only seen in penumbra
Umbra Sun E Penumbra Umbra does not touch the Earth View from the Earth Annular Solar Eclipse • Moon too far from Earth to cover Sun completely -- umbra does not reach the Earth
Umbra Total Eclipse Sun E View from Earth Penumbra Total Lunar Eclipse • Moon pases through umbra of the Earth.
Penumbral Eclipse View from Earth Penumbral Eclipse • Moon only passes through penumbra. Umbra Total Eclipse Sun E Penumbra
Partial Eclipse Umbra Total Eclipse Sun E Penumbral Eclipse Penumbra View from Earth Partial Lunar Eclipse • Moon partially passes through umbra.
Why are there few eclipses? • Orbit of moon is tilted with respect to Earth’s orbital plane by 5° • Line of Nodes = position where moon and earth’s orbital planes intersect
Line of Nodes • When the moon is on the line of nodes it is crossing the Earth’s orbital plane • At other times moon is slightly above or below the Earth’s orbital plane • If moon crosses the line of nodes near a new or full phase an eclipse will occur