(The original article, written by was published on space.com)
Typically, during the course of a year, about a dozen comets will come within the range of amateur telescopes. Most quietly come and go with little fanfare, but some are particularly noteworthy.
During the upcoming weeks, a newly-discovered comet will be making a relatively close approach to the Earth. On Feb. 1, comet C/2022 E3 (ZTF) will pass within 28 million miles (42 million km) of our planet, its first approach in 50,000 years. While this will no doubt entice many skywatchers to attempt to view the comet, whether or not one will actually be able to see it will depend on a variety of factors including location and light pollution from both natural and artificial sources.
Discovery and history
On March 2, 2022 astronomers Frank Masci and Bryce Bolin using the Zwicky Transient Facility (ZTF) at the Palomar Observatory in Southern California, came across an object that they initially identified as an asteroid. It appeared very dim — it was estimated at magnitude +17.3 — or nearly 25,000 times fainter than stars at the threshold of detectability using just the human eye. Subsequent observations revealed that this star-like object possessed a very tightly condensed coma, indicating that it was in fact, a comet. It was the third such object discovered in the fifth half-month (A, B, C, D, E) of the year, so it received the designation C/2022 E3 (ZTF). At the time, the comet was situated 399 million miles (643 million km) from the sun, or just inside the orbit of the planet Jupiter.
After enough observations were gathered to compute an orbit, astronomers determined C/2022 E3 to have an orbital period of roughly 50,000 years. Its last passage through the inner solar system apparently came during the Upper Paleolithic or Old Stone Age. If we take these calculations at face value, then the last people to look up and witness this visitor from the depths of the outer solar system were likely very early Homo sapiens or Neanderthals.
But this may very well be the last time that C/2022 E3 comes our way again. The latest orbital elements suggest that the comet is currently traveling on an orbital path with an eccentricity of 1.00027, or in other words, a parabolic orbit. Such an orbit is not closed, so after it sweeps around the sun C/2022 E3 will move back out into deep space, never to return again. So, this will be the comet’s last time to “perform” for us. We know that comets are composed primarily of frozen gases that are heated as they approach the sun and made to glow by the sun’s light.
We call this cloud of gas the head or coma.
As the gases warm and expand, particles of dust that were embedded in the comet’s nucleus are also released into space. The solar wind blows this material out into an appendage we call the tail. To observers of antiquity, comets resembled a stellar head trailed by long hair, so they called comets, “hairy stars.”
Bright among “common” comets
Comets can be broken down into two basic categories:
Bright comets — the kind that can excite those of us without binoculars or telescopes — appear on average perhaps two or three times every 15 to 20 years. The last such comet to do that was comet NEOWISE (C/2020 F3) in July 2020.
Then there are the common comets, of which most are only visible either with good binoculars or a telescope. The vast majority of comets fall into this category, but C/2022 E3 (ZTF) may end up ranking as exceptionally bright so far as most common comets go, since for a short while it may hover right at the cusp of naked-eye visibility (for those fortunate enough to be blessed with dark, non-light polluted night skies).
For a comet to become readily visible without optical aid, it usually needs to approach closer to the sun than the Earth (92.95 million miles or 149.56 million km). But at perihelion (its closest approach to the sun) on January 12th, C/2022 E3 will get no closer than 103.4 million miles (166.4 million km). It will then begin to move away from the sun. Most comets, however, continue to remain quite active for a few weeks after passing the sun and this will be good so far as the comet’s visibility for us is concerned.
In fact, during the few weeks following perihelion, the orbital geometry between the comet and the Earth has the distance between the two rapidly shrink. That distance will decrease by nearly 40 million miles (64 million km) between Jan. 12 and Feb. 1. As a result, the anticipated increase in the comet’s brightness during that timeframe is expected to correspondingly increase, perhaps more than five-fold.
The closest approach to Earth (perigee) will come at 1:11 p.m. EST on Feb. 1 at a distance of 28,390,710 miles (42,471,730 km).
Where to find it and viewing prospects
Right now, C/2022 E3 is a predawn object, located in the constellation of Corona Borealis at a declination near +34°; it rises in the northeast shortly after midnight. On Jan. 12, the date of its closest approach to the sun, the comet will have shifted several degrees to the northwest. From then onward, its movement against the background stars will progressively increase westward as it approaches the Earth.
The comet will move into northern Boötes on the 14th, and for most mid-northern latitude locations, it will become circumpolar (remaining above the horizon at all times) by the 20th.
On the nights of Jan. 26 and Jan. 27, it can be conveniently found passing several degrees to the east of the bowl of the Little Dipper. On the evening of Jan. 27, it will be 3.5° to the upper right of orange Kochab, the brightest of the two outer stars in the bowl. On the evening of Feb. 1, when C/2022 E3 (ZTF) is passing closest to Earth, it will be within the boundaries of the vague and dim constellation of Camelopardalis. By Feb. 5, it will pass within a couple of degrees to the west of the brilliant yellow-white star Capella and the next night it will be within the triangle that makes up “The Kids” asterism in Auriga and will be located almost directly overhead at around 8 p.m. local standard time.
A number of different predictions have been made regarding the brightness of C/2022 E3 (ZTF) as it passes closest to Earth at the start of February. I believe, based on observations of C/2022 E3 through early January, that the forecasts of Japanese comet expert Seiichi Yoshida(opens in new tab) and Dutch comet expert Gideon Van Buitenen(opens in new tab), will be close to the truth, indicating a magnitude of no fainter than +7.5 during early January and peaking near +5 by the Feb. 1 perigee.
Assuming that its brightening trend remains on target, the comet should become faintly visible with the unaided eye by the third week of January.
Keep your expectations low
But as compelling as this all may sound; I now must temper any excitement by providing a very important disclaimer.
Later this month, many people with binoculars and small telescopes will no doubt attempt to follow the path of C/2022 E3 across the night sky. But actually seeing it will strongly depend on your observing site. From locations that are plagued by light pollution, I’ll bet that sighting this comet is going to prove to be a rather difficult task. And even for those who are blessed with dark and starry skies, finding the comet could prove to be a bit of a challenge. This is because as the comet gets closer to Earth it will become rather large in angular size — perhaps appearing nearly as large as the moon by the start of February — as well as appearing rather diffuse.
Indeed, many with little observing experience will sharply question the predictions for a fifth or sixth-magnitude object. But remember, you’re not looking for a sharp star-like object, but rather something that is spreading its light out over a comparatively large area.
In fact, under a completely dark sky, free of light pollution, perhaps the best instruments for locating the comet will be your own two eyes, especially if you use averted vision.
