There is an especially large and bright full moon coming out tonight. So, if you want an exceptionally good look at some of the stunning features on the lunar surface, this evening will be the night to look for them.
Tonight's full moon is what is called a supermoon, which can appear between 12 percent to 14 percent larger and shine 25-30 percent brighter than normal, according to TimeandDate.com. And this evening's supermoon is the last one of the year. We won't see another one like it until 14 November 2016.
While the physical Moon will not actually grow in size, it will appear bigger in the night sky because it is slightly closer to Earth than normal - a point in the lunar orbit called perigee.
Below is a photo that shows a supermoon on the right compared to an average full moon on the left:
Marcoaliaslama/Wikimedia
Whenever any celestial body reaches its closest approach to Earth - whether it is the Moon, Mars, or a comet - astronomers call that moment perigee. The Moon reaches perigee about once every time it completes its elliptical orbit around Earth, which takes about 27 days. On average, the Moon is 238,800 miles (384,311 km) from Earth, but at perigee it is 225,804 miles (363,396 km) away.
Although the Moon reaches perigee regularly, that doesn't mean that once every 27 days we're treated to a supermoon, like this one from 2013 showing the supermoon rising above the Umaid Bhawan Palace:
A supermoon can only happen when two events line up in time: perigee and a full moon. (You can also have a supermoon during a new moon, but we cannot see new moons, so the event would be anti-climactic, to say the least.) This magical alignment, shown in the illustration below, only happens between three to four times a year, according to EarthSky.org.
And as it turns out, we'll have a decent match tonight: The Moon reached perigee at exactly 8:59am ET this morning and will be fullest at 8:05am ET on Tuesday, October 27.
This article was originally published by Business Insider.
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