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Bruce BettsSeptember 24, 2015

Mega Hemorrhaging Total Lunar Eclipse Sept 27-28, 2015

There will be a spectacular total lunar eclipse on the night of September 27/28.  The lunar eclipse will be visiible from the Americas, Europe and Africa.  Here is some general info about lunar eclipses, followed by specific information, including on timing, for this lunar eclipse.

Eclipse Science Review

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 it 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. 

Mega Hemorrhaging Moon

Making this eclipse even a bit cooler, the Moon will appear somewhat larger than average because it will be near perigee (closest point to the 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 (farthest point from Earth in its orbit). Another informal term given to lunar eclipses sometimes due to their red color (explained below) is Blood Moon. But hey, if we're going to make up names to sell an already really cool event, let's go all the way. I think we should refer to this lunar ecliipse as a Mega Hemorrhaging Moon. Who's with me?

So, why does an eclipsed often appear red?  Check out this Random Space Fact video to learn more:

When to Look

The eclipse is on the night that begins on September 27, but for some of you, e.g., in Europe, the eclipse will begin after midnight, so on the 28th. For those on the west coast of the Americas, the Moon will rise already partially eclipsed, and for those in eastern Europe, it will set while still partially eclipsed.

The times of the key events of the eclipse are shown in the table below. The table includes entry and exit from the penumbra, the penumbral parts of the eclipse. The penumbra is a much fainter shadow – part of the sunlight 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 would be when you are in the umbra. The umbra is the good part for the casual observer. It will be hard to detect the dimming in 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, the start and end of total eclipse – when the Moon is fully within the shadow – and the time the Moon leaves the umbra which will appear to the end of the eclipse.  In ball park terms, you'll notice there is about an hour of partial (umbral) eclipse followed by a little over an hour of total eclipse followed by another hour of partial eclipse.

Penumbral Eclipse Begins:  00:12 UT  17:11 PDT  20:11 EDT
Partial Eclipse Begins:  01:07 UT  18:07 PDT  21:07 EDT
Total Eclipse Begins:  02:11 UT  19:11 PDT  22:11 EDT
Greatest Eclipse:  02:47 UT  19:47 PDT  22:47 EDT
Total Eclipse Ends:  03:23 UT  20:23 PDT  23:23 EDT
Partial Eclipse Ends:  04:27 UT  21:27 PDT  00:27 EDT
Penumbral Eclipse Ends:  05:22 UT  22:22 PDT  01:22 EDT


If you want more detail on the eclipse, you can study this diagram from NASA's Eclipse web site:

This will be the last in a set of four total lunar eclipses in a row, given the fun name “tetrad.” The next partial lunar eclipse will be August 7, 2017, and the next total lunar eclipse will not occur until January 31, 2018. 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 to hear more about the eclipse, and sample my monster truck rally voice?  Then, check out this interview of me with A Martinez on KPCC's Take Two:

Want a little more explanation of eclipses? Watch the first ten minutes or so of my online lecture from last Spring semester done with California State University Dominguez Hills (more class info here).

Read more: lunar eclipse, the Sun, the Moon, explaining science

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society
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