A comet spotted by a space telescope has suddenly brightened enough to be visible to the naked eye – giving new hope to skywatchers disappointed by recent comets that failed to be easily seen.
The new comet can be seen this weekend after sunset, above the northwestern horizon as it moves farther from the Sun.
It’s named after the Neowise space telescope that first detected it on March 27. Most comets are not bright enough to be seen from Earth, but Comet Neowise showed early promise.
"As soon as we saw how close it would come to the Sun, we had hopes that it would put on a good show," said University of Arizona astrophysicist Amy Mainzer, the principal investigator for NASA’s Neowise mission.
Comet Neowise survived its closest approach to the Sun, when it was most in danger of breaking apart from gravitational forces, last Friday, July 3.
It will pass within 65 million miles of the Earth on July 22, before heading once more for the far reaches of the solar system on a roughly 6,800-year orbit.
The comet’s nucleus is a 3-mile wide “dirty snowball” left over from the formation of the solar system about 4.6 billion years ago, said astrophysicist Karl Battams of the U.S. Naval Research Laboratory in Washington, who studies comets that near the Sun.
“They’re collections of rock and dust, all bound together with frozen ices and gases,” he said.
As a comet gets closer to the Sun, on an orbit that can take tens of thousands of years, the frozen gases start to boil off, and the vaporized gas and dust spread out behind the nucleus to create its visible tail.
Comet Neowise actually has two distinct tails, one of gas and one of rocky dust, that point in slightly different directions because they react differently to the movement of the comet and the solar wind of charged particles that stream from the Sun, Battams said.
The comet’s recent surge in brightness could mean that the Sun’s heat has reached volatile pockets near the surface of the nucleus, explained astronomer John Bortle of Stormyville, New York, who has studied comets for more than 50 years.
Comet Neowise was at its brightest when it was closest to the Sun, but it is now entering a better position in the sky for observing it.
“Soon it will recede from the morning twilight in which it has been mired this week and become much better seen, perhaps making it look brighter temporarily to most observers,” Bortle said in an email.
Two other promising comets in the last year fizzled out at this stage and never became bright enough to be easily seen.
But the new comet has already been seen by observers around the world and by astronauts on the International Space Station.
A video from the ISS of Comet Neowise rising above the Earth has also been released on YouTube.
Comet Neowsie is not expected to grow as bright as a “great comet,” such as Hale-Bopp in 1997, but it’s one of the brightest this century, outshone only by Comet McNaught in 2007.
From July 11, the comet’s fuzzy nucleus should be visible to the naked eye soon after sunset, just above the horizon in the northwest, while binoculars could reveal its much larger but faint tail pointing away from the Sun.
Over the following days the comet will climb higher in the northwestern night sky before it disappears to the eye in August, although it will still be visible by telescope.