Comet NEOWISE May Get so Bright It Is Visible With Naked Eye in July

A recently discovered comet known as NEOWISE (C/2020 F3) is speeding towards the sun in its orbit around our star, and some astronomers are predicting it may become visible to the naked eye by early July.

The comet, which was first spotted by NASA's NEOWISE space telescope on March 27, 2020, is currently more than 138 million miles from Earth and is set to make its closest approach to the sun on July 3.

Astronomers expect the comet to increase in brightness, reaching peak magnitude by July, when it could potentially be visible with the naked eye. However, the behavior of comets is notoriously unpredictable so it is difficult to estimate how bright it will get at this stage.

Comets are "cosmic snowballs" made up of frozen gases, dust and rock that orbit the sun. As they approach our star, these fragile constructs are blasted with increasing amounts of radiation, a process that often produces two vast tails of gas and dust.

It is not unusual for comets that have not traveled through the inner solar system before to disintegrate as they pass the sun, as is thought to have occurred with Comet ATLAS (C/2019 Y4) in March and Comet SWAN (C/2020 F8) in May. Both of these objects were initially predicted to become very bright comets, but this situation never materialized.

"As comet-hunter and astronomy writer David H. Levy likes to say, 'Comets are like cats. They have tails and do what they want,'" Rick Fienberg, a spokesperson for the American Astronomical Society, told Newsweek. "There's definitely a chance that Comet C/2020 F3 (NEOWISE) will reach naked-eye brightness, but there's also a chance that it won't, and we have no way of knowing which outcome is more likely at this point.

"You'll recall there was lots of talk of Comet C/2019 Y4 (ATLAS) reaching naked-eye visibility earlier this spring, and then it broke apart as it neared the sun, fading dramatically and never becoming the spectacle that it had been predicted to become. Same thing could happen here, or we could get luckier and have a bright comet in our skies next month."

When we measure the brightness of astronomical objects, the brighter an object is, the lower its magnitude. For example, an object with magnitude 2 is brighter than one that has a magnitude of 8. As of now, NASA's Jet Propulsion Laboratory Horizons system estimates Comet NEOWISE (C/2020 F3) to have a magnitude of around 10—referred to as 10th magnitude—and this same data indicates that it will peak at about 6th magnitude.

However, the Comet Observers Database (COD) says the comet is currently around 7th magnitude, and this estimate may be more accurate than the Horizons figure, because it uses an average of the values reported in recent observations.

Based on the COD observed magnitude, Fienberg predicts that the comet will reach 4th magnitude at its brightest, although some forecasters are predicting it could become even brighter—2nd or 3rd magnitude—if it survives. This would make it easily observable in the northern hemisphere evening sky in mid-July, according to Tony Phillips, author of SpaceWeather.com.

To put this in context, the faintest stars visible with the naked eye have magnitudes of around 6.5. However, a range of factors—including a person's eyesight, atmospheric conditions and location—can affect whether or not an object can be seen unaided.

comet
Stock image: Artist's illustration of a comet. iStock

"Comet brightnesses are easy to misinterpret," Fienberg said. "In a dark, moonless sky far from city lights, the faintest stars visible to the unaided eye are what we call 6th magnitude. Brighter stars have smaller magnitudes, and a difference of 5 magnitudes equals a brightness ratio of 100, i.e., a 1st magnitude star is 100 times brighter than a 6th magnitude star.

"From my rural New Hampshire observing site, a 6th magnitude star is indeed visible to the naked eye under good conditions. From Boston, though, a 6th magnitude star is never visible to the unaided eye because of all the city's light pollution; you're lucky to see 4th magnitude stars there. So observing conditions matter."

Stars are also points, with all their light concentrated into a tiny spot. Comets, meanwhile, are extended, with their light spread out. So in general, no part of a 6th magnitude comet will be visible to the unaided eye even in a dark rural location on a moonless night, according to Fienberg.

"Then there's another problem," he said. "Comets are generally brightest when closest to the sun, and that means they're often brightest in twilight at dusk and/or dawn, which means they are not observable in a dark sky. That means they have to be even brighter to be visible with the naked eye."

Michael Mattiazzo, a renowned amateur comet observer, predicts that Comet NEOWISE (C/2020 F3) has a better shot of surviving its close approach to the sun, or perihelion, than comets ATLAS and SWAN based on the available data so far.

"I'd say there's a 70 percent chance this comet will survive perihelion. Comet NEOWISE could be a case of third time lucky," Mattiazzo told SpaceWeather.com.

"The comet has had a stable light curve unlike the other two comet failures earlier this year. This would indicate that it is a larger object and more likely to survive," Mattiazzo told Newsweek. "If the comet survives its solar encounter on July 3, when it will be within the orbit of Mercury, it could become a reasonably bright object, the brightness of a 3rd magnitude star. By the end of July we could expect it to have faded beyond naked eye range."

If you would like to observe Comet NEOWISE from North America, Fienberg said the object will be visible very low in the northeast, near the sunrise position, before dawn for several weeks centered on July 6.

"The comet will be highest after the 6th but fading, and sunrise will be coming, so you'll be racing against the clock to spot the comet before it gets washed out by the brightening sky. Binoculars will help even if it's a naked-eye object," he said.

"Binoculars, depending on the size and quality, typically extend your view by several magnitudes. They're especially useful for finding the comet; once you know where it's located, you can put down the binoculars and try to spot the comet with your eyes. If the comet ends up sprouting a long tail, you might see the tail before you see the head of the comet, as the tail will be higher in the sky—it points away from the sun. Telescopes aren't particularly good for bright comets, as they show such a tiny piece of the sky."

To track the movements of the comet through the night sky and its position in the solar system, visit The Sky Live.

This article was updated to include additional comments from Michael Mattiazzo.

Comet NEOWISE May Get so Bright It Is Visible With Naked Eye in July | Tech & Science