Our Moon stands out in comparison to other moons in our solar system in that it so large in comparison to its host planet – 27% the size of the earth, making it the fifth largest satellite in our solar system with a diameter of 2,159 miles. Many scientists consider the earth-moon system to be a twin planetary system. The Moon orbits the earth with a period of 29 days. The Earth-Moon distance varies between 238,855 miles at closest approach (perigee) to 252,623 miles at its maximum orbital distance (apogee).
With an orbital period of 29 days, a full moon usually occurs at least once in each calendar month. In the rare cases where two full moons fall within a calendar month, the second full moon is called a “Blue Moon”.
A full moon is labeled a “Super Moon” when the full moon occurs within a few days of the moon’s closest approach to earth. The apparent diameter of the moon at perigee is 14% larger than at apogee and the increase in its brightness can be as much as 30%.


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For a particular occurrence it may only be visible from a limited swath of the earth or take place during daylight hours, further reducing the opportunity to observe the event. The photo above shows the occultation of the 1.0 magnitude star “Aldebaran” (Alpha Tauri) as it is about to be occulted by the dark-limb of the moon – the Moon being only 83% of full at this time.
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