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This weekend is set to start off with a cosmic bang.

On Friday night, the full moon will be eclipsed by the shadow of the Earth, and in the darkness of Saturday morning, just hours after the eclipse, a green-tinted comet will make its closest flyby of Earth.

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This skywatching coincidence should make for an interesting start to the weekend for people around the world who are able to see both the comet and the eclipse.

First, an eclipse

The shadow of the Earth should start encroaching on the face of the moon's surface starting at around 5:30 p.m. ET and lasting for 4.5 hours as the moon dips deep into Earth's outer shadow -- known as the penumbra -- and comes back out again.

A diagram of how lunar eclipses work.Credit: Sky & Telescope illustration

If you have a view of the moon during that period of time, you should be able to see at least part of the penumbral eclipse.

The Friday eclipse won't be like a dramatic total lunar eclipse, which can turn the moon a deep shade of red, but a penumbral eclipse is still beautiful in its subtlety.

"The outer part of Earth’s penumbra is so pale that you won’t notice anything until the Moon’s edge has slid at least halfway in," Alan MacRobert, a senior editor at Sky & Telescopemagazine, said in a statement. "So start looking about 90 minutes before mid-eclipse."

The shadow should start encroaching on the moon's left side, slowing moving inward and then slowing moving in reverse as the moon comes out of its dip into Earth's shadow.

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A view of a penumbral eclipse in 2012.Credit: Hong Kong Space Museum/Sky & Telescope

"With time, the dusky shading will become more prominent, and as mid-eclipse approaches, the lopsidedness of the moon’s illumination will be totally obvious," Sky & Telescope added in the statement.

The northern bit of the moon's face should look slightly darker than the rest of the lunar surface, the magazine added, because it will be the bit closest to the deep shadow of the Earth, known as the umbra.

Then, a comet

Once the eclipse ends, the next bit of our cosmic weekend can start in earnest.

In the wee hours of Saturday morning, Comet 45P will make its closest approach with Earth, bringing it nearer to our planet than any other comet has been in about 30 years.

The comet won't be visible with the naked eye, but if you have a pair of binoculars -- or even better a backyard telescope -- they should at least give you some sense of what this icy wanderer looks like.

During this close approach, Comet 45P will fly about 7.4 million miles from Earth.

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"It'll be visible in the morning sky in the constellation Hercules," NASA said in a skywatching video. "The comet then passes through the constellations Corona Borealis (the Northern Crown), Boötes (the Herdsman), Canes Venatici (Boötes' hunting dogs) and Ursa Major. Then on to Leo by the end of February."

If you don't catch the comet this time, don't worry, you'll have another chance to see it when it comes back around in 2022, according to NASA.

If you aren't in a part of the world that affords you the ability to see the comet and lunar eclipse -- or if it's cloudy in your area -- then the skywatching organization Slooh has you covered.

Slooh will air two live broadcasts to share live views of the comet and the lunar eclipse with expert commentary. The live eclipse broadcast will begin at 5:30 p.m. ET, with the comet show set for 10:30 p.m. ET on Slooh's website.

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(责任编辑：知識)