March full moon 2021: Catch the big 'Worm Moon' (and 1st 'supermoon' of the year) on Sunday

The full moon of March, called the Worm Moon, will occur  on Sunday (March 28), at 2:48 p.m. EDT (1817 GMT). 

Two days later, the moon will reach perigee, the nearest point to Earth in its orbit. This means the moon will appear slightly larger than usual in the night sky and may be referred to as a “supermoon” (by some definitions), according to NASA. The near-full moon will also share the sky with a planetary conjunction, but only for Southern Hemisphere skywatchers. 

The full moon will be in the constellation Virgo, and have an angular diameter (apparent size) of 33 arc minutes, slightly larger than the average of 31 arc minutes across. An arc minute is one-sixtieth of a degree, so the difference in size to most people won’t be noticeable. (For reference, your clenched fist held at arm’s length measures about 10 degrees wide.)

Related: Full moon names (and more) for 2021

A supermoon?

Learn what makes a big full moon a true “supermoon” in this Space.com infographic. (Image credit: Karl Tate/Space.com)

The reason the full moon will appear larger than usual is that on Tuesday (March 30) at 2:13 a.m. EDT (0613 GMT), the moon will be at perigee, or its closest to the Earth for this orbit, according to NASA. The moon’s orbit isn’t a perfect circle, and at perigee it will be 360,309 kilometers form the Earth, versus an average 384,400 kilometers (240,000 miles). 

When the full moon coincides with perigee it is sometimes called a “supermoon” — but in this case the full moon will miss perigee by about 35 hours. “Supermoon” isn’t an official technical term used by astronomers, and the term is somewhat arbitrary. Whether a full moon counts as “super” depends on how close to the full moon the user of the word thinks perigee should be. 

“Supermoons have