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Astronomy

Dennis Mammana: Get Ready for a Total Lunar Eclipse

Get ready for a total lunar eclipse this month.
Get ready for a total lunar eclipse this month. (Dennis Mammana photo illustration)

Early on the evening of Tuesday, Jan. 30, watch as the sun sets behind the western horizon. Then face the opposite direction and you’ll soon spot the moon rising in the east.

On that night, the moon’s phase will be full, and regular readers of this column know that the full moon does everything opposite of the sun. When the sun sets in the west, the full moon rises in the east; and when the sun rises in the east, the full moon sets in the west.

Perhaps you’ve never considered watching the full moon set, but this might be the time to set your alarm to do so. Why? Because on the morning of Wednesday, Jan. 31, the setting moon will be experiencing one of nature’s great sky shows: a total eclipse.

On that morning, all sky watchers throughout North America will see the start of this eclipse — weather permitting, of course — but depending on where you live, you may see only a portion of the sky show. In general, the farther west you live, the more of the eclipse you will be able to see before the moon sets.

A lunar eclipse occurs when the full moon slips into the shadow of the Earth far out in space. This occurs every six months or so when the sun, moon and Earth are aligned. Sometimes the moon only partially enters the shadow and we see what’s called a partial eclipse. Other times it passes near the shadow’s center and we see the moon fully engulfed, a total lunar eclipse.

Such a sky show is remarkable to watch, but this one is no normal eclipse. Well, actually, it is, but if you believe what you read on the Internet, it’s unlike no other and will surely be life-altering. Not only will there be a total eclipse of a full moon (of course, it can’t happen any other way!) but this full moon will also be the second in January.

This is what is known as a blue moon, since it happens ... well ... only once in a blue moon. A blue moon isn’t as rare as it might seem; since the moon’s synodic period (29.53059 days) doesn’t match up exactly with the calendar months, we get two full moons in the same month about every 2.72 years, or about 3 percent of the time.

The Jan. 31 full moon also happens to lie near its perigee, its closest orbital point to Earth. This, of course, occurs every month, but when it happens around the time of a full moon, folks love calling it a “supermoon.” There’s nothing super about it, really; it appears only about 7 percent larger than the average full moon — about the size difference between a 15-inch pizza and a 16-inch pizza — and is hardly noticeable without measuring it.

OK, so there you have it. On the morning of Jan. 31, we will experience a total eclipse of a full, blue and super moon. Next week, I’ll tell you more about this upcoming sky show, the times it will occur and how to view it.

In the meantime, get those aluminum foil hats ready. ... No sense taking chances!

Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at [email protected] and follow him on Twitter: @dennismammana. Click here to read previous columns. The opinions expressed are his own.

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