Angular Size and Distance
Angular Size and Distance
Angular Size and Distance
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<strong>Angular</strong> <strong>Size</strong> <strong>and</strong> <strong>Distance</strong>
Relevant Geography
Earth’s Rotation• 23 hours <strong>and</strong> 56 minutes relative to backgroundstars (sidereal period)• Spin axis of Earth defines points on the celestialsphere (using north <strong>and</strong> south poles)– North Celestial Pole– South Celestial Pole– Celestial Equator• Sky appears to rotate east to west about thecelestial poles because Earth rotates west to east.
The Celestial Sphere
Earth Orbits Sun
The Ecliptic
Tilt of Spin Axis
The Equinoxes <strong>and</strong> Solstices• Tilt of the spin axis is related to the seasons• Effect of tilt on climate is not instantaneous
Ecliptic on the Celestial Sphere
Celestial Coordinates
Motion Depends on Declination
Circumpolar Constellations• Circumpolar constellations never set.• Circumpolar constellations change withlatitude… sky changes with latitude
Precession of the Earth’s Axis
North Celestial Pole Changes
Moon Orbits the Earth
Lunar Phases
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