Look hard and you can see Comet Lovejoy lighting up the night sky
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“Comets this bright [appear only] every few years, on average,” says Matthew Knight, a research scientist who studies comets at Lowell Observatory in Flagstaff, Arizona. Indeed, some viewers with keen sight might be able to spy it with the naked eye from a location far from urban lights— think the Arizona desert or Michigan's Upper Peninsula.
But most skywatchers will probably benefit from a telescopic lens. The good news is that binoculars— say, a pair of 10 x 50s— should do the trick, according to Dean Regas, outreach astronomer at the Cincinnati Observatory. “The farther away from the city lights you can get, the better,” he adds.
Prime viewing conditions start right after dark, when bright stars emerge. Comet Lovejoy (officially designatedC/2014 Q2) will appear highest in the southern sky at around 8 or 9 p.m. The loftier it is, the less atmosphere you'll be peering through, and the better you'll be able to see it, Regas says.
“It's definitely bigger than the stars that are also in the field, [and] you can see it moving. If you're there for half an hour, you can tell that it's moved relative to the stars nearby,” Knight says.
You might even notice a green glow. How come? When ultraviolet light from the sun hits gas molecules in the comet's coma, they get excited. To return to a stable state, those molecules release energy at different wavelengths.
"The one that we happen to see most easily with the human eye is the one that's in the middle of where our eyes are [most] sensitive"— that is, the green region of the visible spectrum, Knight explains.
The molecules responsible for the green glow are pairs of carbon atoms, called diatomic carbon. Other gas molecules in the coma emit energy when they're excited, too— just not at wavelengths that we can see, or not at the same intensity as diatomic carbon's.
But Regas says that many viewers won't notice the green tint; humans don't see colors that well in dim light. Instead, they'll see what he describes as a “gray fuzzball.”
Using an instrument that lets in more light, like a telescope instead of basic binoculars, might help you detect the green halo. And “cameras are more sensitive to colors in dim light than the human eye is,” Regas says, which explains the impressive images that photographers have been rolling out.
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