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The Moon - Introduction
Magnitude : +12.5, 25 000 times brighter than a first magnitude star.
The Moon is actually very dark: it only reflects about 11% of the light that hits it. That makes it about as dark as slate! The reason it looks so bright is is that it is sitting in full sunlight, and so there is a lot of light hitting it.
The albedo of the maria is about 0.05 and that of the highlands ia about 0.10. The apparent difference appears greater when viewed with the eye etc., but this is a contrast effect.
At full Moon its illumination is about 12 times as great as at quadrature.
The Moon subtends an angle of approximately 1/2 a degree in the sky -
a very useful fact to remember sometimes when trying to search for stars in the sky.
To be more precise the maximum angle subtended is 33 minutes 31 seconds, and the minimum angle
29 minutes 22 seconds.
It is tilted at 5.15 degrees to the plane of the Earh's orbit.
Its average distance from Earth is 384.400 km (maximum distance
406.697 km; minimum distance 356.410 km).
The time it takes for one revolution
around its orbit about the Earth, the sidereal month, is exactly the
same as the time taken to
rotate on its own axis - 27.32 days (27 days 7 hours 43 minutes 11.5 seconds).
The time it takes to adopt the same attitude in the sky as perceived by us, e.g. between two Full Moons is called the synodical month. This has an average length of
29 days 12 hours 44 minutes 2.8 seconds. In January it is about 6 hours longer than this and in July it is about 6 hours less.
Its mean orbital velocity is 3680 km/h (1.02 km per second).- by virtue of
it traveling on an ellipse, its orbital velocity will be greater when it is nearer to us
than when it is further away.
Its orbital eccentricity is (on average) 0.054.
Its mass is 1/81 (0.012) of that of the Earth.
Its density is 3.34 tonnes / m3 , about 60% of the Earth's density (water has
a density of 1 tonne / m3.
Its surface gravity is 0.165 that of Earth.
Day and night are both approximately 14 Earth days long.
The surface temperature varies between 120 degrees in the "day" to -130 degrees at "night".
So far, 380kg of moon rock has been returned to Earth.
Since 1977, all the experiments laid out by the Apollo missions have been shut off.
It is smaller than Mercury ( 4878 km diameter ) but larger than Pluto ( 2300 km diameter )
It is slighter smaller than Io ( 3642 km diameter ) and is larger than Europa ( 3140 km in diameter ). It is smaller than Ganymede ( 5260 km in diameter ) and Callisto ( 4810 km diameter ).
It is smaller than Saturn's largest satellite Titan ( 5150 km in diameter ).
It is twice as large as the largest satellite of Uranus.
It is larger than Neptune's largest satellite, Triton (2700 km in diameter ).
Nevertheless, it is unusually large for a satellite when compared with its parent planet -
its Equatorial Diameter is 3476 km , compared with 12.756 km for the Earth
Its escape velocity is 2.38 km/s.
The highlands account for about 85% of the surface. 15% is covered by the maria. On the near side, maria account for about 30% of the surface.
Its maximum diameter is 33' 31". Its minimum is 29' 22".