Moon watchers will be greeted tonight with a rare and beautiful supermoon that's significantly larger than usual moons, according to NASA.

Supermoons - a colloquial term - have two characteristics.

One, it has to be a full moon, meaning it appears as a full circle. This happens about once every 29 days when the moon moves to the complete opposite side of the sun with the earth in the middle. When this happens, the sun illuminates the full visible side of the moon, thereby giving it a complete circular shape.

Two, the moon's distance needs to be close to the earth. The moon's orbit is oval, so on some parts of the orbit it will be closer to the earth and on other parts it will be farther. For it to qualify as a supermoon, the orbit needs to within 10 percent of the closest point to earth on the orbit.

When these two characteristics coincide, a supermoon is seen.

However, tonight's supermoon is even closer to the earth compared to other supermoons.

One, it's going to be within 1 hour of the closest point, according to Geoff Chester of the US Navy.

Two, moon orbits are not the same and have different perigees (the closest point to earth); the current moon orbit has a closer than usual perigee, according to the National Geographic.

According to NASA, the best time to look [at tonight's supermoon] is when [it] is near the horizon.

Tonight's supermoon will be visible pretty much any time during the night, said Geza Gyuk, astronomer at the Adler Planetarium in Chicago, reported the National Geographic.

The following are past instances of signficant supermoons:

  • November 10, 1954
  • November 20, 1972
  • January 8, 1974
  • February 26, 1975
  • December 2, 1990
  • January 19, 1992
  • March 8, 1993
  • January 10, 2005
  • December 12, 2008
  • January 30, 2010

The following are future predicted instances of signficant supermoons:

  • November 14, 2016
  • January 2, 2018
  • January 21, 2023
  • November 25, 2034
  • January 13, 2036