A big question for skygazers in the coming weeks is what will become of a recently discovered comet heading for a late April rendezvous with the Sun. The new visitor has apparently entered the inner solar system from the Oort Cloud.
The Oort Cloud is a vast, thick-walled spherical cloud believed to be the primary source of untold billions of comets. The extreme limits of this cometary cloud are thought to reach some 15 trillion miles into space.
The new object is Comet Pan-STARRS, officially known as C/2021 O3 (Pan-STARRS), discovered on July 26, 2021 by astronomers using the Panoramic Survey Telescope And Rapid Response System, or “Pan-STARRS” telescope . a 70.9-inch (1.8 meter) Ritchey-Chretien reflector stationed in Haleakala, Hawaii.
Related: Amazing photos of Comet Leonard in the night sky
Do you see the comet?
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If you’re looking for binoculars or a telescope to see Comet Pan-STARRS or other objects in the night sky, check out our guides to the best binoculars and telescopes. If you need photography gear, our best cameras for astrophotography and best lenses for astrophotography can help you prepare for the next celestial sight.
When discovered last summer, Pan-STARRS was 402 million miles (648 million kilometers) from the Sun – beyond the orbit of Jupiter – and 355 million miles from Earth. At the time, the comet was about 400,000 times fainter than the faintest star visible to the naked eye.
But by its upcoming perihelion (closest point to the Sun) on April 21, its distance from the Sun will have shrunk to about 26.7 million miles (42.9 million km), putting it well in Mercury’s orbit. Such a huge change in solar distance would typically cause a comet to increase its intrinsic luminosity by about 16 magnitudes, potentially making it visible to the naked eye. Additionally, PanSTARRS will make its closest approach to Earth on May 8 at a distance of approximately 56 million miles (90 million km).
Out of sight
At this moment the comet cannot be observed thanks to its proximity to the sun. In fact, the last “reliable” observation by Japanese observer Ken-ichi Kadota dates back to February 1st. At that time it was still very weak. It would certainly be helpful if we could monitor the comet’s brightness over time to see how it’s evolving and whether or not it’s brightening as predicted, but unfortunately that’s not possible in this particular case; We can only guess what’s going on in terms of Pan-STARRS performance to date.
After orbiting the sun and heading back into space, Pan-STARRS will slowly move out of bright sunlight and into early evening twilight skies by the end of this month.
By then it could be as bright as the sixth magnitude, suggesting that it’s at least faintly visible to the unaided eye under dark skies, although it’s far more visible with binoculars or telescopes. We should note that Magnitude is the degree of brightness of an object in the sky. The smaller the magnitude, the brighter the object. The brightest stars in the sky are zero or first magnitude. The faintest stars visible to the eye on dark, clear nights are sixth magnitude. First magnitude stars are 100 times brighter than sixth magnitude stars).
Not easy to see
Sixth magnitude is the kind of magnitude that would still make Pan-STARRS a decent comet from the perspective of a seasoned amateur astronomer. But as of this writing, it doesn’t look like this comet will turn into such a spectacle Comet NEOWISE was 2020 or Comet Leonard last December when he attracted public attention. And because it will be fairly low in the west-northwest sky, it could be very difficult for newcomers to astronomy to pick up.
You may have your best chance of making a sighting on the evening of May 2nd, when you can use three prominent celestial objects to point the way to Pan-STARRS. These three objects will be a crescent moon, the planet Mercury, and the Pleiades star cluster.
Scan with binoculars low over the west-northwest horizon about 45 to 50 minutes after sunset. You should be able to see the narrow part of the moon well just over two days into the new phase. Then, 4 degrees below the Moon, you’ll see a bright “star” glowing yellow-orange. That will be the planet Mercury. And about 3 degrees below Mercury, you should be able to find the tiny silver cloud of stars that makes up the Pleiades.
Now using the distance between the Pleiades and the Moon’s position as a kind of celestial ruler, and using binoculars, check the part of the sky at a similar distance – about 6 degrees – as to the upper right of the Pleiades. If Comet Pan-STARRS lives up to its modest expectations, you may see a circular, faint patch of light, with perhaps a short tail, rising almost vertically from the horizon.
It’s high… it’s far… it’s gone!
In the nights that follow, the comet will move rapidly northward, gaining height in the northwestern sky. His projected path takes him through the constellations Perseus (May 4-10) and Camelopardalis (May 11-28). On May 8th, the same day it will be closest to Earth, Pan-STARRS will become circumpolar for observers living north of the 40th parallel; that is, it stays above the horizon all night, neither rising nor setting. After that, it will retreat from both the Sun and Earth back to the far reaches of the solar system.
On May 27 it will pass closest to Polaris, the North Star (8.5 degrees), but by that time it will have faded significantly compared to earlier in the month. Current estimates are that it will decrease to the seventh magnitude by May 7th, to the eighth magnitude by May 13th, to the ninth magnitude by May 19th, and to the tenth magnitude by May 27th.
Although this is where the screenplay detailing the upcoming performance of Pan-STARRS was written, it’s worth noting that Comets are notoriously bad actors. Just to prove how fickle comets can be, both Comet NEOWISE and Comet Leonard were high flyers and turned out brighter than originally predicted.
Neither of these comets were expected to put on a big show, but in its brightest form, NEOWISE reminded many of a miniature version of Comet Hale-Bopp, while Leonard displayed several unexpected bursts of activity that more than doubled its expected brightness while showing numerous wore streamers. Kinks and knots that changed the shape of its narrow bluish ion tail.
That being said, Comet Pan-STARRS could also brighten unexpectedly and give us a real surprise. Still, few celestial events have a greater potential for false alarms than these interplanetary vagabonds.
Unfortunately, the odds that Pan-STARRS could outperform aren’t very good. As previously mentioned, orbital calculations suggest it comes straight out of the Oort Cloud; thus making its first ever visit near the sun. We know from observations of other comets with a similar pedigree that they tend to perform poorly.
Such “new” comets, moving in parabolic orbits, may be covered with volatile material such as frozen nitrogen, carbon monoxide, and carbon dioxide. This ice evaporates far from the Sun, giving a distant comet a short-lived burst of brightness that can raise unrealistic expectations. Arguably the most notable example of these comet flops was the infamous Kohoutek in 1973.
Other Oort cloud comets, which had approached unusually close to the Sun, dissipated before fully orbiting it. Comet ISON in 2013 did just that. Unfortunately, some astronomers believe this will eventually doom Pan-STARRS as well. We’ll just have to wait and see.
If he manages to survive, this will be his only visit to the sun. Pan-STARRS is then hurled down a path that will take it completely out of the solar system, never to return.
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Joe Rao serves as an instructor and visiting professor at New York University Hayden Planetarium. He writes on astronomy for Journal of Natural Historythe Peasant Almanac and other publications. Follow us on Twitter @spacedotcom and further Facebook.
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