There's a "blood moon" on the rise. This week the moon will disappear for the second time in 2014, in a total eclipse early Wednesday morning.
Lunar eclipses happen when the sun, moon, and Earth are aligned just right for Earth's shadow to cover the moon—and turn it a ruddy hue.
"It's rare and an awesome spectacle to look at," says Ben Burress, an astronomer at the Chabot Space & Science Center in Oakland, California.
"Cultures in the past often feared eclipses, thinking that something bad was happening," he says. "But now with those fears removed by scientific understanding of what's going on, that leaves only enjoyment." (Related: "Solar Eclipse Myths From Around the World.")
Why Is a Blood Moon Rare?
A lunar eclipse happens when the moon passes behind Earth and into our planet's shadow. The moon orbits Earth every 28 days or so, so why the moon isn't eclipsed every time it moves behind our planet? The answer lies in the tilted orbit of the moon, which usually puts it a bit out of alignment with the Earth and sun. The straight alignment needed for an eclipse usually happens only once every few years.
This year is one of the rare years with multiple lunar eclipses. Wednesday's will be the second in a series of four—a tetrad—over two years. That pattern won't repeat for another 20 years or so.
Much of North America will have front-row seats for this special sky show, which will particularly favor the western part of the continent. Sky-watchers there will be able to see the entire eclipse unfold high in the western skies; East Coast observers will see much of the first half of the eclipse. For early risers in the East, the full moon will be sinking below the western horizon around sunrise, just as the total eclipse is getting under way.
Eclipse watchers in Hawaii, Australia, and much of the Pacific region, including Japan, also will get a chance to see the entire eclipse unfold, though in their evening hours. In South America only the early stages of the eclipse—when Earth's shadow begins to cover the moon—will be visible, since the moon sets at dawn.
Folks in Africa, Europe, and the Middle East will be on the wrong side of the planet when the eclipse is happening, so the moon won't even be in their skies.
When Will the Eclipse Happen?
The eclipse begins with the partial phase, when the moon enters Earth's dark shadow (also called the umbra shadow). That begins at 2:15 a.m. PDT (5:15 a.m. EDT). Then the umbral shadow will spread across the moon's disk, moving from left to right.
At 3:25 a.m. PDT (6:25 a.m. EDT) totality begins, when the moon is fully engulfed in the umbral shadow and turns a shade of orange red. The deepest or midpoint of the eclipse will be at 3:55 a.m. PDT, and totality continues until 4:24 a.m. PDT. The last phase of the partial eclipse ends at 5:34 a.m. PDT.
What's the Most Exciting Part of the Eclipse?
"Seeing the first dark 'bite' taken out of the moon's edge is startling and pleasing—unusual, unexpected," Burress says. "But by far the best part of the eclipse is totality, when the full moon has darkened to orange and red hues and starts to look much more like a three-dimensional object.
"Sometimes the moon can darken so much you have to actually look for it, and then there is this copper ball or blood orange hanging in the sky."
Lunar eclipses are safe to watch with the naked eye, unlike solar eclipses. (A solar eclipse occurs when the moon passes between the Earth and the sun.) (Related: "How to Safely Watch a Solar Eclipse.")
Why Is a Blood Moon Red?
During the total phase of the eclipse, sunlight shining through the ring of Earth's dusty atmosphere is bent, or refracted. The red part of the light is cast onto the moon's surface.
"The redness in an eclipse is caused by the same phenomenon as when a colorful orange or red sunset illuminates the landscape around you with its light," Burress says.
Viewers see the lunar disk go from dark gray during the partial phase of the eclipse to reddish orange during totality.
The exact color of a blood moon varies, depending on the amount of dust in the Earth's atmosphere at the time. Active volcanoes spewing tons of ash into the upper atmosphere, for instance, can trigger blood-red eclipses.
Before an eclipse, no one can predict precisely what color we'll see.
When Will the Next Lunar Eclipse Happen?
This will be the second in a series of four lunar eclipses across two years visible from North America—one about every six months or so. (The first was on April 15, 2014.) If you miss this one, the next will be on April 4, 2015; the last in the tetrad will be on September 28, 2015.
Both of the next two eclipses will be visible from all of North America except the West Coast. People out West will have a long wait for their next lunar eclipse, until January 31, 2018.