Historic 'blood moon' lunar eclipse visible Wednesday morning

A historic lunar eclipse will be visible in the morning sky on Wednesday in Minnesota — another visit by a so-called "blood moon."

Update: See photographs of the 'blood moon' lunar eclipse

The phenomenon has that name because of the red cast of the moon as it passes completely through the shadow of our planet. Sunlight scattered through the atmosphere shines a red glow on the moon, even as it passes through the dark middle of the Earth's shadow.

This month's total eclipse is calculated to start at 5:24 a.m. and end about an hour later in Minnesota, according to the U.S. Naval Observatory. The moon will be setting in the southwestern sky, a short distance above the horizon.

Visibility isn't a sure thing. The National Weather Service in Chanhassen is predicting partly cloudy skies with temperatures of about 40 degrees.

Another complication: The sun will be coming up at 7:19 a.m., just after the eclipse happens. It's a rare phenomenon astronomers call "selenelion," a nearly simultaenous sunrise and lunar eclipse.

"Physically, its called the 'impossible eclipse,'" said Tim Young, a professor at the University of North Dakota in Grand Forks.

He said the sun and moon "are supposed to be exactly in a line with each other, and with the Earth, so we shouldn't be able to see them both at the same time, but the Earth's atmosphere refracts the light from each of them, so it looks like its above the horizon a little bit."

And that will only happen in part of the country, generally east of the Mississippi River, along what's called the "terminator line."

Space.com says that means the eclipse may only be visible for a short time:

"Depending on the clarity of your sky, you might have up to roughly 10 to 15 minutes before sunrise for the sky to still be dark enough, and the moon to be high enough above any horizon haze for it to be clearly visible. And keep in mind that this holds only for the uneclipsed portion of the moon. You might, however, be able to mitigate the effects of a brightening sky somewhat by using binoculars or a telescope."

Lunar eclipse watchers may have to get creative, according to Sally Brummel, planetarium education and outreach coordinator at the University of Minnesota's Bell Museum.

"Because its going to be so low on the horizon, you have to have a very clear view, with no trees or buildings in the way," she said.

The University of North Dakota's Sun Earth Moon System will be live streaming the event if weather permits, starting at 3:30 a.m. You can watch it here.

It may be worth the trouble of getting up and going outside before dawn.

In addition to the simultaneous sunrise and eclipse of the moon, it's also the second in a two-year series of four historic eclipses, each at six month intervals.

The first was in April, and two more will happen next year. Astronomers call the phenomenon a tetrad of eclipses — a relatively rare series of four total eclipses of a full moon.

Overall, lunar eclipses are common. They typically happen about twice a year. They also occur in various forms, as penumbral, partial or total clipses. They aren't always visible in the United States.

But 2014 and 2015 are different. There are four total eclipses in a row, on April 15 and Oct. 8 this year, and April 4 and Sept. 28 next year. They'll all be visible in Minnesota, weather permitting.

There are only 142 of these tetrads from 2000 B.C. through the year 3000. Nine of those tetrads will happen this century, but they have been much rarer in the past: There were no tetrads for more than 300 years 1582 to 1908, according to NASA.

So, set your alarm and get up early for a little bit of astronomical history tomorrow morning.