Does the Moon Rotate?


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** Does the Moon Rotate? **

by Fraser Cain on October 14, 2008

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Full moon. Image credit: NASA

Does the Moon rotate on its axis? Full moon. Image credit: NASA

The Moon is familiar; it always looks the same. We know that the Earth
rotates, that’s why the Sun, Moon and stars seem to move through the sky
every day. But does the Moon rotate? And if the Moon rotates, why do we
alway see the same side – it never seems to change.
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Well, the Moon does rotate. In fact, the Moon takes 27.3 days to turn once
on its axis. But the Moon also takes 27.3 days to complete one orbit around
the Earth. Because the Moon’s rotation time is exactly the same amount of
time it takes to complete an orbit, it always presents the same face to the
Earth, and one face away.

Because it only presents one face to the Earth, astronomers say that the
Moon is tidally locked to the Earth. Although the Moon looks like a
perfectly smooth ball, it has slight differences in the shape of its
gravity field. A long time ago, the Moon did rotate. But each time it
turned, the Earth’s gravity tugged at it, slowing down its rotation until
it only presented one face to the Earth. At that point, the Moon was
tidally locked, and from our perspective, it doesn’t seem to rotate.

Many other moons in the Solar System are


does the moon rotate

Moon - Wikipedia, the free encyclopedia


** Moon **

From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article is about Earth's Moon. For moons in general, see Natural
satellite. For other uses, see Moon (disambiguation).
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The Moon Moon symbol
Full moon in the darkness of the night sky. It is patterned with a mix of
light-tone regions and darker, irregular blotches, and scattered with
varying sizes of impact craters, circles surrounded by out-thrown rays of
bright ejecta.
Full moon as seen from Earth's northern hemisphere
Adjective lunar, selenic
Orbital characteristics
Perigee 363,295 km
(0.0024 AU)
Apogee 405,503 km
(0.0027 AU)
Semi-major axis 384,399 km
(0.00257 AU)^[1]
Eccentricity 0.0549^[1]
Orbital period 27.321582 d (27 d 7 h 43.1 min^[1])
Synodic period 29.530589 d (29 d 12 h 44 min 2.9 s)
Average orbital speed 1.022 km/s
Inclination 5.145° to the ecliptic^[2] (between 18.29° and 28.58°
to Earth's equator)^[1]
Longitude of ascending node regressing by one revolution in 18.6 years
Argument of perigee progressing by one revolution in 8.85 years
Satellite of Earth
Physical characteristics
Mean radius 1,737.10 km  (0.273 Earths)^[1]^[3]
Equatorial radius 1,738.14 km (0.273 Earths)^[3]
Polar radius 1,735.97 km  (0.273 Earths)^[3]
Flattening 0.00125
Circumference 10,921 km (equatorial)
Surface area 3.793 Ã— 10^7 km^2  (0.074 Earths)
Volume 2.1958 Ã— 10^10 km^3  (0.020 Earths)
Mass 7.3477 Ã— 10^22 kg  (0.012300 Earths^[1])
Mean density 3.3464 g/cm^3^[1]
Equatorial surface gravity 1.622 m/s^2 (0.165 4 g)
Escape velocity 2.38 km/s
Sidereal rotation period 27.321582 d (synchronous)
Equatorial rotation velocity 4.627 m/s
Axial tilt 1.5424° (to ecliptic)
6.687° (to orbit plane)^[2]
Albedo 0.136^[4]
Surface temp. min mean max
equator 100 K 220 K


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