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The Moon is Earth's only natural satellite. It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have synchronized the Moon's orbital period (lunar month) with its rotation period at 29.5 Earth days, causing the same side of the Moon to always face Earth.
The lunar distance is on average approximately 385,000 km (239,000 mi), or 1.28 light-seconds; this is roughly 30 times Earth's diameter or 9.5 times Earth's circumference. Around 389 lunar distances make up an AU astronomical unit (roughly the distance from Earth to the Sun).
Thus, the angular diameter of Earth's orbit around the Sun as viewed from a distance of 1 pc is 2″, as 1 AU is the mean radius of Earth's orbit. The angular diameter of the Sun, from a distance of one light-year, is 0.03″, and that of Earth 0.0003″. The angular diameter 0.03″ of the Sun given above is approximately the same as that of a ...
Finally, because the Moon is only about 60 Earth radii away from Earth's centre of mass, an observer at the equator who observes the Moon throughout the night moves laterally by one Earth diameter. This gives rise to a diurnal libration , which allows one to view an additional one degree's worth of lunar longitude.
Across different full moons, the Moon's angular diameter can vary from 29.43 arcminutes at apogee to 33.5 arcminutes at perigee—a variation of around 14% in apparent diameter or 30% in apparent area. [5]
English: Comparison of angular diameter of the Sun, Moon and planets with the International Space Station (as seen from the surface of the Earth), the 20/20 row of the Snellen eye chart at the proper viewing distance and typical human visual acuity. The dotted circles represent the minimum angular size (when the celestial bodies are farthest ...
At inferior conjunction (for the terrestrial observer, this is the opposition of Mars and the Sun), the maximum visible distance between the Earth and the Moon would be about 25′, which is close to the apparent size of the Moon in Earth's sky. The angular size of Earth is between 48.1″ and 6.6″ and of the Moon between 13.3″ and 1.7 ...
The method relies on the relatively quick movement of the moon across the background sky, completing a circuit of 360 degrees in 27.3 days (the sidereal month), or 13.2 degrees per day. In one hour it will move approximately half a degree, [1] roughly its own angular diameter, with respect to the background stars and the Sun.