So far, 2019 has been a treat for astronomy fans. The last supermoon (and the brightest one of the year) was visible on February 19, and the next one is set to appear barely a month later on Wednesday, March 20, the first day of spring. Instead of the snow moon that came last month, this upcoming celestial event will be a super worm moon.

What is a supermoon?

A supermoon is defined as the Moon's seemingly larger size when viewed from Earth. The Moon is constantly circling our planet, and its apparent size in the night sky changes depending on where it is in its oval-shaped orbit. Its perigee is the point in its orbit that brings it closest to Earth; when the Moon reaches its perigee on a day when it's full, it's officially a supermoon.

Full moons also have different nicknames based on the time of year they occur. Last month's event was a snow moon: the first full moon that appears in February. March's supermoon will be a worm moon. A worm moon is usually the last full moon of winter, and it's named after the earthworms that start wriggling their way through the soil as spring approaches. In this case, the full moon coincides with the vernal equinox—the start of the spring season. The last time a full moon coincided with the first day of spring was March 20, 1981.

When to watch the next supermoon

The best time to catch the next supermoon are the nights of Tuesday, March 19 and Wednesday, March 20. At 2:48 p.m. on Tuesday, the Moon will reach its perigee, and at 8:43 p.m. ET on Wednesday, the Moon will be at its fullest. The Moon will also appear especially close and bright on the days surrounding the spring equinox.

Supermoons have felt like a common occurrence this year, with three appearing in the first three months in 2019. But after the worm moon, they will be much rarer: The next supermoon with a full moon won't happen until 2020. There will, however, be two new moon supermoons in August, but even though the Moon will be at the closest point in its orbit during the events, it won't be visible in the night sky.