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• Rotation
– The turning, or spinning, of a body on its axis.
– Responsible for our days and nights.
– Mean solar day is the timer interval from one noon to the next, about 24 hours.
– Sidereal day is the time it takes for Earth to make one complete rotation
(360 °) with respect to a star other than the sun – 23 hours, 56 minutes, 4 seconds.
• Revolution
– The motion of a body, such as a planet or moon, along a path around some point in space.
– Perihelion is the time in
January when Earth is closest to the sun.
– Aphelion is the time in July when Earth is farthest from the sun.
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• Earth’s Axis and Seasons
– Because the Earth is tilted on its axis, this changes the angle of light received from the sun.
– This change in angle of light is responsible for the
Earth’s seasons.
• Precession
– Is the change in direction in which the axis of the
Earth points.
– This change occurs about every 26,000 years.
– When this happens,
Polaris will no longer be our “North Star.” Instead it will be the star Vega.
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• Earth-Sun Motion
– The sun revolves around the galaxy.
– Therefore the solar system itself is moving in the direction of the star Vega
• at 20km/sec
• 12.5 miles/sec
• 45,000 miles/hour
– The galaxies are also in motion.
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• Perigee is the point at which the moon is closest to
Earth.
• Apogee is the point at which the moon is farthest from Earth.
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• The phases of the moon are due to the motion of the moon and the amount of moon that is lit by the sun.
• These changes occur monthly.
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• The synodic month is based on the cycle of the moon’s phases. It lasts
29 ½ days.
• The sidereal month is the true period of the moon’s revolution around Earth.
It lasts 27 1/3 days.
• These cycles are due to the Earth-moon system moving in an orbit around the sun.
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– The moon’s period of rotation about its axis and its revolution around Earth are the same,
27 1/3 days.
– It causes the same lunar hemisphere to always face earth.
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• Solar eclipses occur when the moon moves in a line directly between
Earth and the sun causing a shadow on
Earth.
• Lunar eclipses occur when the moon passes through Earth’s shadow.
• During a new-moon or full-moon phase, the moon’s orbit must cross the plane of the ecliptic for an ellipse to take place.
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