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Super Blue Moon total lunar eclipse coming January 31
January 21, 2018
Worldwide map via the US Naval Observatory showing the day and night sides of Earth at the instant of the greatest eclipseJanuary 31 at 6:30 a.m. Pacific Time. Greatest eclipse happens at the same instant worldwide; you must be on the night side of the world to witness it. The shadow line at the left depicts sunrise (moonset) January 31, and the shadow line at right represents sunset (moonrise) January 31. Since the total eclipse lasts more than one hour, if you live somewhat east (right) of the sunrise line, you can still catch a total or partial eclipse low in the west before sunrise (and before greatest eclipse). Or if you live somewhat west (left) of the sunset line, you can still catch a total eclipse low in the east after sunset (and after greatest eclipse).
By Bruce McClure

The Blue Moon – second of two full moons in one calendar month – will pass through the Earth’s shadow on January 31 to give us a total lunar eclipse. Totality, when the moon will be entirely inside the Earth’s dark umbral shadow, will last a bit more than one-and-a-quarter hours. The January 31 full moon is also the third in a series of three straight full moon supermoons – that is, super-close full moons.

It’s the first of two Blue Moons in 2018. So it’s not just a lunar eclipse, or a Blue Moon, or a supermoon. It’s all three … a super Blue Moon eclipse!

If you live in North America or the Hawaiian Islands, this lunar eclipse will be visible in your sky before sunrise on January 31.  On the other hand, if you live in the Middle East, Asia, Indonesia, Australia or New Zealand, this lunar eclipse will happen in the evening hours after sunset on January 31.

In the Pacific Standard Time Zone, the partial umbral eclipse begins at 3:48 a.m., total eclipse begins at 4:52 a.m., greatest eclipse will be at 5:30 a.m., total eclipse ends at 6:08 a.m., and partial umbral eclipse ends at 7:11 a.m., though the moon may set before end of partial umbral eclipse.

Is it the first Blue Moon total eclipse in 150 years, as some claim? Well … It depends on where you live. Yes, we’ve seen the social media memes going around suggesting this is the first Blue Moon total eclipse in 150 years.

But the meme is true only for time zones in and around the Americas, not for the rest of the world. The last time that we had a Blue Moon total lunar eclipse – reckoning in world time – was December 30, 1982.

That wasn’t a Blue Moon eclipse for the Americas, however. For us, the full moon previous to the total lunar eclipse fell on November 30 – not December 1.

Before that, there was a Blue Moon total lunar eclipse for the world’s Eastern Hemisphere (Asia, Indonesia, Australia and New Zealand) on December 30, 1963.

Okay, now, finally we get to it. Before that, in late March 1866, there was a Blue Moon total lunar eclipse for North and South American time zones.

By the way, the next Blue Moon total lunar eclipse will happen on December 31, 2028.

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In any umbral lunar eclipse, the moon always passes through Earth’s very light penumbral shadow before and after its journey through the dark umbral shadow.

A partial lunar eclipse precedes the total eclipse by a little over one hour, and follows totality for a little over one hour.

So, from start to finish, the moon takes three hours and 23 minutes to totally cross Earth’s dark umbral shadow. Eastern North America can see beginning stages of the partial umbral eclipse low in the west before sunrise January 31, whereas portions of the Middle East and far-eastern Europe can view the ending stages of the partial umbral eclipse low in the east after sunset January 31.

South America, most of Europe and Africa won’t be able see this eclipse.

Incidentally, a very light penumbral eclipse comes before and after the dark (umbral) stage of the lunar eclipse. But this sort of eclipse is so faint that many people won’t even notice it. The penumbral eclipse would be more fun to watch from the moon, where it would be seen as a partial eclipse of the sun.

A lunar eclipse can only happen at full moon. Only then is it possible for the moon to be directly opposite the sun in our sky, and to pass into the Earth’s dark umbral shadow.

Most of the time, however, the full moon eludes the Earth’s shadow by swinging to the north of it, or south of it. For instance, the last full moon on January 2, 2018, swung south of the Earth’s shadow. The next full moon – on March 2, 2018 – will swing north of the Earth’s shadow.

The moon’s orbital plane around Earth is actually inclined at five degrees to the ecliptic – Earth’s orbital plane around the sun. However, the moon’s orbit intersects the ecliptic at two points called nodes. It’s an ascending node where it crosses the Earth’s orbital plane going from south to north, and a descending node where it crosses the Earth’s orbital plane, going from north to south.

In short, a lunar eclipse happens when the full moon closely coincides with one of its nodes, and a solar eclipse happens when a new moon does likewise. It’s not a perfect alignment this time around, with the moon turning full about five hours before the moon crosses its ascending node. But that’s close enough for this full moon to stage a total lunar eclipse that lasts a touch more than one and a quarter hours.
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