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Late night yields almost total eclipse

Another Blood Moon is on the way! Catch a nap this Thursday afternoon because later that night we'll have a lunar eclipse beginning after 2 a.m. on Friday morning.

It's not officially a total lunar eclipse, but it's about as close as it can be to one. Total lunar eclipses are also known in our pop culture world as Blood Moons. Despite that menacing moniker, the Blood Moon should be enjoyed and certainly not feared.

Lunar eclipses, or Blood Moons if you insist, occur when the Earth is nearly in a straight line between the sun and the moon and the moon slips into the Earth's shadow, as you can see in the diagram.

The Earth doesn't have to be in an exact line between the sun and the moon, because at the distance of the moon, the Earth's umbra shadow is around 5,500 miles wide. Since the moon is less than 2,200 miles in diameter, getting into the Earth's shadow isn't a huge accomplishment. There's plenty of the Earth's shadow to go around.

We don't have a lunar eclipse every full moon because the moon's 27.3-day orbit around the Earth tilts by five degrees in respect to Earth's 365-day orbit around the sun. Because of that, the full moon misses the Earth's shadow most of the time.

This time around, however, the full moon is full at one of the two points where the moon's orbital plane intersects the Earth's orbital plane — the right place at the right time for a total lunar eclipse.

Very early Friday morning, the full moon will be shining very high in the Butler southern sky. After 2:18 a.m., you'll start to see the moon begin to darken on its upper right side. Over the next several hours the darkening will continue to increase, advancing to the lunar disk's left side. The circular edge of the shadow is visual proof that the Earth is indeed round.

At 4:04 a.m., the moon will be almost totally eclipsed. I say almost because all but the extreme lower left edge of the moon will be darkened. The moon could take on an orange hue or sport a bloody red hue.

No one can really predict what shade the eclipsed moon will take on. Only the shadow knows — the Earth's umbra shadow that is. The umbra shadow is not completely dark because some of sunlight does manage to get through Earth's atmospheric shell, as you can see in the diagram.

The light that does get through is bent and strained as it comes through our atmosphere. All of the blue and yellow components of the light are scattered away, leaving just the red to bathe the eclipsed moon.

The shade of the red light reaching the moon depends on the atmospheric conditions on Earth that the filtered sunshine passes through on its way to the moon.

No matter what shade of red the moon takes on, it will be beautiful and perfectly safe to view. You don't have to look through any special glasses or anything.

An occasional gander through a telescope at the eclipsed moon is nice. Still, I think it's a wonderful experience to watch it with just your natural eyesight or maybe a pair of binoculars.

After 4:04 a.m., the Earth's shadow on the moon will gradually retreat. The moon is totally out of Earth's shadow at 5:47 am.

I hope you enjoy the lunar show in the wee hours of Friday morning. If you want to make sure you don't lose too much sleep you may want to set your alarm for around 3:30 a.m. Friday morning, just in time to watch totality a half hour later.

If you can't handle the hours of this lunar eclipse at all, you're going to have to wait until May 15 and 16 of next year for the next Blood Moon. Totality for that eclipse begins around 11:30 p.m.

Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Contact him at mikewlynch@comcast.net.