What has a green head, a long white tail and is a half-mile wide?
Comet Nishimura, of course.
Haven’t heard of it? That’s probably because it was only recently discovered last month by space photographer Hideo Nishimura of Japan. Stargazers in the Northern Hemisphere will have their last chance to see Comet Nishimura on Tuesday as it passes close to Earth and slingshots around the Sun back into space, not to return for another 435 years.
How to catch the comet
Comet Nishimura is currently visible throughout the Northern Hemisphere. But it will be the most visible on Tuesday, Sept. 12, when it’s closest to Earth — a mere 78 million miles away.
The best time to see it will be about two hours before sunrise just above the horizon. Although the comet looks green in photos, to the naked eye it will look like a small streak and can be found to the lower left of Venus, which looks like a bright speck just above the eastern horizon. For astronomy enthusiasts, it will be to the left of a bright star in the Leo constellation, called Regulus, according to Space.com.
While the comet can be seen with the naked eye, the best way to view it is with a telescope or binoculars in a location with little light pollution and an unobstructed horizon.
After Sept. 13, Northern Hemisphere stargazers will no longer be able to see Nishimura as it swings closest to the Sun on Sept. 17, according to NASA.
If Nishimura doesn’t disintegrate from its close encounter with the Sun, Southern Hemisphere observers should be able to see the comet by the end of the month during the evening.
Why it’s green, but it’s tail is white
Comets like Nishimura have green heads, but the emerald hue doesn’t extend to their tails. The reason for this was a mystery that was only recently solved by scientists.
“The green color is caused by diatomic carbon, a highly reactive molecule that is created from the interaction between sunlight and organic matter on the comet’s head and then almost immediately destroyed again by the Sun’s energy before it can move far from the nucleus,” Kate Howells explains in the Planetary Society.
Though the green-and-white comet will brighten each day, it will become harder to spot from Earth as it gradually drops lower in the sky.