The band of turquoise across the moon, caught during a total lunar eclipse on December 21, 2010, is from sunlight filtered through the ozone layer. Image by Alan Dyer and spaceweather.com
For 59 minutes early Wednesday morning, the moon will turn an eerie shade of copper red when it passes through the Earth’s shadow in a total lunar eclipse.
And if the skies are clear enough and you look at just the right moment, you might glimpse a band of turquoise stretching across the moon’s face. That turquoise is caused by the ozone in the upper atmosphere, which blocks out the red light and enhances the blue.
“You have to be a black-belt eclipse watcher to see it,” said Tony Phillips, an astronomer with spaceweather.com. “It’s kind of like a challenge. Like the ozone challenge. Can you see the turquoise?”
A partial lunar eclipse occurs when the moon skims the outskirts of the Earth’s shadow. During a total eclipse, also known as a blood moon, the moon plunges through and gets swallowed up by that shadow. This happens when the sun, moon and Earth are aligned. The Earth blocks the sunlight that is normally reflected off the moon, making the moon appear red, the color of an Earth’s sunset.
The shadow cast by Earth consists of two concentric cones, the penumbra, the pale outer shadow, and the umbra, the shadow’s inner core.
“This Wednesday, the moon will pass through the dark red core of Earth’s shadow — that’s the umbra, Phillips said. “The moon is not crossing dead center through the umbra. It can be a little out of alignment and we still get a lunar eclipse. That’s what’s happening here.”
Imagine, Phillips said, that you were standing on the surface of the moon during a total lunar eclipse. The Earth directly overhead would be blocking the sun, so you’d be seeing its night side. But you’d also see what looks like a ring of fire surrounding the planet.
“You’d be simultaneously seeing every sunset and sunrise happening around the Earth at the same time,” he said.
Wednesday’s eclipse will be the second of four consecutive lunar eclipses – that’s known as a tetrad — occurring in a two-year timespan that are visible in the United States. That’s unusual. From 1600 to 1900, for example, there were no tetrads at all, Phillips said.
The event will start at 6:25 a.m. ET and end at 7:24 a.m., and the best viewing conditions in our country will be in the West, along with the southern United States from Mississippi to the Carolinas and across Northern Florida, said Alex Sosnowski, senior meteorologist at accuweather.com. A storm system rolling through New England could deliver cloud cover that obscures the moon in the northeastern United States.
“As you head farther north in the northeastern states, you’ll have more cloud cover and rain, which could just totally foil the view,” Sosnowski said.
Phillips is one of many scientists who study the colors created as sunlight filters through the Earth’s upper atmosphere to understand more about the climate. Tomorrow morning, his team will fly a camera on board a helium balloon to photograph the eclipse from the stratosphere. Scientists have used this technique to photograph meteor showers from balloon payloads in the upper atmosphere, but it will be a first for a lunar eclipse.
“We want to know, what would the lunar eclipse look like if you could get above the atmosphere of our planet,” he said.
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