If weather cooperates, people all over the Western Hemisphere on Sunday will be able to see a “super blood moon” eclipse.
The total lunar eclipse begins at about 8:30 p.m. in the St. Louis area. Totality — when the Earth completely blocks the sun from the moon — will occur after 10:40 p.m., as the moon turns a dull shade of red.
The moon also will appear large, because it will be at a point in its elliptical orbit that’s close to the Earth. Total lunar eclipses happen almost every year, but this exact type of lunar eclipse happens every 18 years, said Brad Jolliff, a professor who studies lunar geochemistry at Washington University.
“You don’t have to wait that long for the next lunar eclipse,” Jolliff said. “There will be another one, just not quite as spectacular.”
The total lunar eclipse will last about five hours and in five phases. The first penumbral phase — when the Earth’s shadow starts to creep across the moon — will last an hour. The subsequent umbral phase — when the Earth’s shadow covers most of the moon — will occur for another hour. Then, totality will occur for a third hour, followed by the reverse of the two former phases.
The moon turns red because when sunlight reaches the Earth’s atmosphere, the gas molecules in the atmosphere scatter blue light, allowing red light to come thorugh.
“If you think about sunset and sunrise, the sunlight is traveling through the atmosphere and you get the nice red colors,” Jolliff said.
It will be easy to watch the eclipse, since the moon will be high in the sky, said Don Ficken, a member of the St. Louis Astronomical Society.
“You could pretty much see it, even if you’re in a subdivision,” Ficken said. “So trees, for the most part, should not be an issue.”
Ficken plans to be at Jefferson College in Hillsboro on Sunday night, where the St. Louis Astronomical Society has organized a public event to view the eclipse. At that location, it’s also dark enough that people might be able to see the Milky Way, he said.
Ficken and Jolliff say moon watchers will not need to use binoculars or a telescope to see the eclipse, but they can help enhance the experience.
There’s much that scientists can learn about the moon during total lunar eclipses, Jolliff said. For example, since the moon does not have an atmosphere to retain heat, its temperature will drop by several hundred degrees during totality. That could have interesting effects on the moon’s geology, he said.
Jolliff is also working with scientists who are a part of China’s Chang'e 4 mission to explore the lunar surface. Recently, the lander reached the far side of the moon, making it the first spacecraft to do so in history.
Editor's note: An earlier version of this story listed a scheduled eclipse watch party at the Department of Energy-owned Weldon Spring Site in St. Charles. It has been canceled due to expected winter weather and safety concerns.
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