Over the next few days, sky-watchers will have the chance to spot a pale green comet zipping by Earth as it makes one of its closest flybys in years.
Comet 45P/Honda–Mrkos–Pajdušáková (or Comet 45P for short) has been slowly brightening since it rounded the sun on New Year’s Eve. As it heads back into the outer solar system, it will pass within 7.4 million miles of Earth—about 32 times farther away from us than the moon.
This relatively close approach will happen at 3 a.m. ET on February 11. During that time, the comet will sweep across early morning skies for observers across the Northern Hemisphere, moving higher over the pre-dawn horizon and out of the twilight glare.
While there is absolutely no chance of Comet 45P colliding with Earth, the flyby will be our nearest brush with any comet in over three decades. In June 1983, Comet IRAS-Araki-Alcock whizzed by our planet at a distance of only 5.9 million miles.
Comet 45P will make its best showing just hours after another celestial event known as a deep penumbral lunar eclipse. This is when the full moon enters Earth’s outer shadow cone, and the normally bright, silvery disk undergoes a subtle but distinctive shading.
The full moon will rise in the east soon after local sunset on February 10 and will begin to darken at 6:14 p.m. ET. Over the course of 90 minutes, the moon will slowly plow deeper in our planet’s shadow, with the darkest part of the eclipse occurring at 7:44 p.m. ET (00:44 UT on February 11).
Skywatchers across North America, Europe, and northwestern Africa will have front-row seats for most, if not all, of the 4.5-hour sky event. For more details, see our complete February sky guide.
Comet 45P was discovered in 1948 by three independent observers, who now share credit in its name. It orbits the sun every five and half years, and the 45P designation refers to the fact that it was the 45th periodic comet to have its orbit calculated.
In the first week of February, keen observers reported that the comet was shining just above magnitude 7. That’s a tad too faint to see with the naked eye, but not too hard to spot with binoculars and small backyard telescopes even from city suburbs.
Photos of the comet show that over the past month, it has unexpectedly lost its tail of gas and dust. The images also show that it sports a distinct green hue. As the comet nears the sun, heat vaporizes ices on its surface, which releases pockets of carbon-based gases. These compounds tend to glow green as they are bombarded by sunlight in the near vacuum of space.
To hunt down Comet 45P before it heads away from Earth, face south about an hour before local sunrise. On Saturday, the comet will be some 70 degrees above the horizon, about equal to a stack of seven clenched fists held at arm’s length. Scan the sky through your binoculars for a small, round, fuzzy patch of light, which will look quite different from the pinpoint lights of stars.
The comet will be nestled within the constellation Hercules, the hero. Creamy-colored Saturn and much brighter Jupiter will be far below it and nearer to the horizon, forming a giant triangular shape.
By Sunday, the comet will slide quickly toward the small constellation Corona Borealis, and on Monday it will be in the constellation Boötes, the herdsman, in the western sky.
The comet’s quick pace across the night sky is due not only to its proximity to Earth but also to its awesome speed. Barreling through the inner solar system at 51,000 miles an hour, the comet traverses about 20 arcminutes of sky—equal to about two-thirds of the disk of the moon—every hour.