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18 Cards in this Set
- Front
- Back
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Lightyear
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~ 9.46 × 10^15 m
the distance light travels in one year |
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Proper motion
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the motions of stars relative to one another
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Celestial poles
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the points where earth's axis intersects the celestial sphere
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Diurnal motion
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the daily progress of the Sun and other stars across the sky
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Ecliptic path
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the apparent motion of the Sun relative to background stars over the course of a year
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Zodiac
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the 12 constellations through which the Sun passes as it moves along the ecliptic
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Summer solstice
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the point on the ecliptic path where the Sun is at its northernmost point above the celestial equator
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Autumnal equinox
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Sept. 21
when the Sun passes the celestial equator moving south |
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Vernal equinox
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March 21
when the Sun passes the celestial equator moving north |
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Tropical year
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365.2422 mean solar days
the interval of time from one vernal equinox to the next |
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Precession
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the change in direction of the earth's axis over the course of time
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Synodic month
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the time required for the Moon to complete a full cycle of phases
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Corona
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the Sun's outer atmosphere
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Umbra
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the central region of the Moon's shadow during a solar eclipse
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Penumbra
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the area of partial solar eclipse - outside the umbra but still in the Moon's shadow
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Annular eclipse
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a Solar eclipse in which the Moon is too far away to cover the Sun
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Line of nodes
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the line joining the points on the Moon's orbit where it crosses the plane of the ecliptic
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Eclipse seasons
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points at which the line of nodes briefly lies along the Earth-Sun line
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