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Walt Heiges with the Sacramento Valley Astronomers Society says the supermoon phenomenon happens when the full moon is closer than usual in its orbit.
Depending on where it is in the sky, a supermoon can play tricks on your eyes.
The first of the three supermoons appeared early on Saturday, July 12. If you missed it, you can catch the ones on Aug. 10 and Sept. 9.
Also watch out, supermoons usually bring higher tides.
The full moon Saturday, July 12, 2014, in Nairobi, Kenya, the "supermoon" the nickname for full moons that happen when our celestial neighbor is relatively close to Earth and which are called a perigee moon by scientists. That distance varies because the moon follows an elliptical orbit. When it s close and full, it appears bigger and brighter than normal, although in fact the difference can be hard to detect. (AP Photo/Sayyid Azim)