When Is the November 2021 Full Moon, Why Is It Called the Beaver Moon?

It's set to be a good weekend for skywatching as the Beaver Moon and a near-total lunar eclipse are set to occur on the same day.

The Beaver Moon is the name given to the full moon in November.

Technically this full moon is due to occur early on Friday morning, November 19, at 3:58 a.m. ET, according to NASA, but it will still appear full for about three days around this time from Wednesday to Saturday.

According to The Old Farmer's Almanac, which lists monthly full moon names from Native American, Colonial American and European folklore, the Beaver Moon's name refers to the time of the year in which beavers take shelter in their lodges to prepare for winter, and also the time in which beaver fur traps would be set up in North America, historically.

Alternative names for the full moon in November include the Whitefish Moon, an Algonquin term referring to the spawning of whitefish, and the Freezing Moon, a word from the Anishinaabe peoples referring to the winter season, sates the The Old Farmer's Almanac.

Full moons occur as part of the lunar cycle, which makes the moon appear to change shape throughout the course of a month. The moon's shape does not actually change, but the amount of sunlight it reflects back to Earth does.

A full moon is when the Earth is located between the moon and the sun, so we see a full side of the moon illuminated.

This month, the Beaver Moon is set to coincide with a near-total lunar eclipse. This means that the moon will start to dim during the night as it passes through the shadow of the Earth—something that generally happens only a couple of times per year.

We can expect the moon to start dimming just after 2:15 a.m. ET on November 19, and it will reach its full dimness at just after 4 a.m. that same morning, according to NASA program executive Gordon Johnston who writes monthly skywatching blogs.

It's due to be the longest lunar eclipse of the century.

The moon will then begin to get brighter once again as it slowly moves out of the Earth's shadow.

Lunar eclipses often give the moon a reddish-brown color. This is because some sunlight hits the moon after passing through the Earth's atmosphere first, which bends the light and causes it to appear red. This same atmospheric effect is what gives us orange sunrises and sunsets.

According to TimeAndDate, which lists upcoming lunar eclipses for the next ten years, there are usually between two and three lunar eclipses per year and they vary in totality.

However, these events are not visible from everywhere on Earth, and can only be seen in certain locations where the moon is out at the time the eclipse takes place. A clear sky also helps.

North America is well-placed to observe the entirety of this weekend's upcoming lunar eclipse.

Full moon
A stock photo shows the full moon against a dark sky. Different names are given to full moons of each month of the year. BrianEKushner/Getty