Your Guide to the Total Lunar Eclipse on 20 January
The last total lunar eclipse for the next two-and-a-half years will occur on the night of 20 January. The lunar eclipse will be visible throughout most of North America, South America, the eastern Pacific Ocean, the western Atlantic Ocean, Europe, and western Africa. A partial lunar eclipse will be visible in other parts of Africa, Europe, and Asia. Greatest eclipse will occur at 05:12 UTC 21 January (00:12 EST 21 January, 21:12 PST 20 January). Here is some general information about lunar eclipses, followed by specific information, including on timing, for this lunar eclipse.
Full Moon and Spica
Full moon during the April 15, 2014 lunar eclipse with the star Spica to the right.
How does a lunar eclipse work?
A lunar eclipse happens when the Moon passes into the shadow of the Earth. Because of the needed geometry, lunar eclipses only happen during Full Moon. But, not all Full Moons produce eclipses because of the tilts of the Earth’s axis (what also causes seasons) and the tilt of the Moon’s orbit. When those line up so the Moon passes through the shadow of the Earth, you get a lunar eclipse. If the Moon passes completely into the darkest shadow (where no direct sunlight reaches it at all, called the umbra), then it is a total eclipse. If things line up not quite right, you may only get a partial lunar eclipse. Lunar eclipses of either kind can be seen from large portions of the Earth: any part for which the Moon is visible during eclipse. The whole process of a total lunar eclipse lasts for a few hours.
Geometry of a lunar eclipse
Why is it called the Super Blood Wolf Moon?
You may see this lunar eclipse referred to as the Super Blood Wolf Moon. What is behind that odd moniker? First off, this eclipse is even a bit cooler, or at least bigger, than usual: The Moon will appear somewhat larger than average because it will be near perigee, the closest point to Earth in its orbit. This has informally and in headlines in recent years been called a Supermoon, referring to when the Moon is full near perigee so appears slightly larger (14% in diameter) than when it is full near apogee, the farthest point from Earth in its orbit. Another informal term given to lunar eclipses sometimes due to their “blood” red color (explained below) is Blood Moon. Moons in different months also get named and January’s is often called the Wolf Moon. So, we get the Super Blood Wolf Moon.
Why does an eclipse often appear red? Check out this Random Space Fact video to learn more:
Why isn't the Moon pitch black during a total lunar eclipse? Dr. Bruce Betts has this week's Random Space Fact!
When to look for the lunar eclipse
The eclipse is on the night that begins on 20 January, but for some of you, e.g., in Europe, the eclipse will begin after midnight, on 21 January.
The times of the key events of the eclipse are shown in the table below. The table includes entry and exit from the penumbra, and the penumbral parts of the eclipse. The penumbra is a much fainter shadow–some of the Sun’s light still falls directly on the Moon. If you were on the Moon, you would see a partial solar eclipse when you are in the penumbra, but a total eclipse when you are in the umbra. The umbra is the good part for the casual observer. It will be hard to detect the dimming from the penumbra, but quite obvious when the Moon starts entering the umbra. So, for the casual observer, I’d focus on the umbra entering time (Partial Eclipse Begins), the start and end of total eclipse – when the Moon is fully within the shadow – and the time the Moon leaves the umbra (Partial Eclipse Ends), which will appear to be the end of the eclipse. In ballpark terms, there is about an hour of partial (umbral) eclipse followed by an hour of total eclipse followed by another hour of partial eclipse.
Penumbral Eclipse Begins:
Partial (Umbral) Eclipse Begins:
Total Eclipse Begins:
Total Eclipse Ends:
Partial Eclipse Ends:
Penumbral Eclipse Ends:
Partial lunar eclipse
Partial lunar eclipse. Note that the shadow of the edge of the Earth is round because the Earth is round.
If you want more detail on the eclipse, you can study this diagram from NASA:
20 January 2019 lunar eclipse details
There will be a partial lunar eclipse 16 July 2019 (visible from S.America, Europe, Africa, Asia, and Australia), but the next total lunar eclipse will not occur until 26 May 2021. So, get out there and see this one. All you need to observe a lunar eclipse is your eyes. And, unlike a solar eclipse, you can stare all you want. It is always fun to use binoculars or a telescope to observe the Moon, but they aren’t needed. Clear skies and good observing!
Want a little more explanation of solar and lunar eclipses? Watch ten minutes or so of my online lecture (from 2017) done with California State University Dominguez Hills (more class info here).