Full Wolf Moon, eclipse on January 10

Above photo: Last year, on January 21, 2019, Tom Wildoner took this photo of the total lunar eclipse from Weatherly, Pennsylvania. Often, a lunar eclipse recurs about 11 days earlier the following year, but this year’s lunar eclipse on January 10, 2020, will be a hard-to-see penumbral eclipse.

In North America, we often call the January full moon the Wolf Moon. These next few nights – January 9 and 10, 2020 – watch for the full-looking moon, our nocturnal sun, to light up the nighttime from dusk till dawn. And if you live in the world’s Eastern Hemisphere, you might – or might not – detect Earth’s faint penumbral shadow on the full moon’s face on the night of January 10-11, 2020.

Penumbral lunar eclipse

Penumbral eclipse over Sabah, North Borneo, from our friend Jenney Disimon on the night of March 23, 2016. Look for the faint shading on the right.

Although the moon appears full to the eye for two or three days in a row, astronomers regard the moon as truly full at a well-defined instant: when the moon is 180 degrees opposite the sun in ecliptic longitude.

Or, another way of looking at it, the moon is precisely full whenever the elongation between the moon and sun equals 180 degrees. Click here to know the present moon-sun elongation, remembering that a positive number means a waxing moon whereas a negative number indicates a waning moon.

Moon phases in the year 2020.

The moon phases for the year 2020 via Astropixels. A = annular solar eclipse, T = total solar eclipse, and n = penumbral lunar eclipse. The year 2020 has 13 full moons, two of which take place in the month of October.

Incidentally, this month’s full moon – the first of 13 full moons in 2020 – falls on January 10, at 19:21 Universal Time. Because we have 13 full moons this year, there are actually two full moons in October 2020, the second of which is commonly called a Blue Moon.

Although the full moon occurs at the same instant worldwide, the clock reads differently by time zone. Here, in the mainland United states, the moon turns full on January 10, at 2:21 p.m. Eastern Time, 1:11 p.m. Central Time, 12:11 p.m. Mountain Time and 11:11 p.m. Pacific Time. So, here in the United States, the full moon will come during our daylight hours, when the moon is still beneath our horizon. That means we’ll miss out on seeing the faint penumbral eclipse in the Americas, but that it’ll be visible in the Earth’s Eastern Hemisphere on the night of January 10-11. See the worldwide map below.

Worldwide map of day and night sides of Earth at full moon.

Day and night sides of Earth at the instant of full moon (January 10 at 19:21 UTC). The shadow line crossing the Atlantic Ocean depicts sunset January 10 while the shadow line at right (going through Australia, represents sunrise January 11. Image via EarthView.

This is the first of this year’s six eclipses (two solar and four lunar), yet it’s the second eclipse of the present eclipse season, the first of which came with the solar eclipse on December 26, 2019. All added up, that’s 7 eclipses (3 solar, 4 lunar), the maximum number of eclipses possible in one 354-day lunar year of 12 lunar months (December 26, 2019, to December 14, 2020).

All four lunar eclipses in 2020 are hard-to-see penumbral eclipses whereby the moon misses the dark umbra but travels through the outer faint penumbra. However, the upcoming penumbral eclipse on the night of January 10-11, 2020, will feature the deepest of the bunch. Your best chance of detecting the slight darkening on the full moon’s face will come at or near maximum eclipse (January 10, 2020, at 19:10 Universal Time). If you want to know when – or if – this eclipse happens in your part of the world, click on TimeandDate.

Chart of penumbral eclipse

On January 10, 2020, the new moon misses the dark umbral shadow but goes through the faint penumbra, to present a barely perceptible eclipse. This eclipse would be more impressive from the moon, where you’d see a partial eclipse of the the sun. See below.

Simulation of Earth partially eclipsing the sun from the moon.

Yes, the eclipse on January 10, 2020, would be more impressive from the moon, where you’d see a a partial eclipse of the sun.

For the Northern Hemisphere, this January full moon presents the first of three full moons of the winter season; and in the Southern Hemisphere, this is the first of three summer full moons. For the world as a whole, this penumbral lunar eclipse features the second eclipse of the eclipse season, the first one staging an annular eclipse of the sun on December 26, 2019.

Because the full moon stands opposite the sun in Earth’s sky, the full moon assumes the sun’s position for six months hence, or in July. From all over the world, this January full moon will shine in front of the constellation Gemini the Twins. Therefore, like the July sun, this January full moon will rise and sets quite far north of due east and west.

In the Northern Hemisphere, that means this January full moon will follow the high path of the summer sun throughout the night.

Yet, in the Southern Hemisphere, where it’s summer, this January full moon will the low path of the winter sun.

But wherever you may reside worldwide, enjoy the first full moon of the year on January 10, 2020, as it lights up the nighttime from dusk till dawn!

Bruce McClure