By Trevor Nace, Forbes
Tonight, skywatchers will be treated to the only supermoon (scientific name: perigee syzygy) in 2017. If you step outside you’ll notice the Moon is especially large and bright, which is because the moon is at its closest distance to Earth.
The perigee moon (prerequisite for a supermoon) exists because as the moon orbits the Earth it does so in an oval or elliptical shape, meaning sometimes the moon is closer to the Earth and other times it’s farther. For a supermoon to exist, there must both be a full moon as well as a perigee moon, hence why the moon tonight will look especially close, full, and bright.
This is your opportunity in 2017 to see a supermoon. The most recent supermoon was around a year ago on Nov. 14, 2016.