On December 3rd of 2017, the last Super Moon phenomenon will appear through the night sky. In this case, the Moon will will appear about 7% larger and 15% brighter than the usual.
Supermoons happen when a full moon approximately coincides with the moon’s perigee, or a point in its orbit at which it is closest to Earth. This makes the moon appear up to 14 percent larger and 30 percent brighter than usual. The moon becomes totally full at 10:47 a.m. EST (1547 GMT) on Sunday (Dec. 3). It will officially reach perigee less than 24 hours later on Monday (Dec. 4) at 3:45 a.m. EST (0845 GMT), when it is 222,135 miles (357,492 kilometers) away from Earth.
The moon’s orbit around Earth is not a perfect circle. It’s an ellipse, a saucer shape that’s longer than it is wide. That means as the moon follows this orbit, it’s sometimes closer to the Earth and sometimes farther away. At perigee, the closest spot in its orbit to the Earth, it’s around 31,068 miles closer to Earth than at apogee, when it’s farthest away.
The only supermoon of the year is slated for Dec. 3, 2017, at precisely 15:47 UTC, according to EarthSky.org. After that, there will be supermoons on Jan. 2 and Jan. 31, 2018. Time your viewing for just after local sunset, National Geographic suggests, when the “moon illusion” will make the orb look especially large and vibrant.