Earth’s Moon. Astronomy Notes Part III. Our Moon. Earth has one natural satellite, the moon. Our moon orbits Earth within a period of about a month. Direction of the moon’s motion is counterclockwise. Orbit is elliptical Perigee- point where moon is closest to Earth
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Earth’s Moon Astronomy Notes Part III
Our Moon • Earth has one natural satellite, the moon. • Our moon orbits Earth within a period of about a month. • Direction of the moon’s motion is counterclockwise. • Orbit is elliptical • Perigee- point where moon is closest to Earth • Apogee- point where moon is farthest from Earth
Moon Phases • Phases: various shapes of the moon lighted by reflected sunlight
waxing: when the size of the visible portion of the moon is increasing • waning: when the size of the visible portion of the moon is decreasing
full moon: entire half of the side of the moon facing Earth is lit • new moon: no lighted area of the moon is visible from the Earth
gibbous: more than half of the side facing the Earth is lit • crescent: less than half of the side facing the Earth is lit
New moon Waxing crescent 1st quarter Waxing gibbous
Full moon Waning gibbous Waning crescent 3rd quarter
Lunar Surface • maria: smooth, dark areas of the moon- reflect little light • maria are plains of dark solidified lava
craters: bowl-shaped depressions on the moon • lunar craters are formed from impacts of debris
Lunar History • The most widely accepted model for the origin of the moon is that when the solar system was forming, a body the size of Mars impacted Earth. • The resulting debris was ejected into space, began orbiting around Earth, and eventually united to form the moon.
Why does the same side of the moon always face us? • Because the moon rotates and revolves at the same speed