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New comet might brighten enough for binoculars


View larger. | Italian amateur astronomer Ernesto Guido was one of the first to confirm the cometary nature of new comet C/2022 E3 (ZTF). Image via his blog.

New comet might be a bright one

On March 2, 2022, astronomers discovered a new comet. It’s still far from the sun, at a distance of 4 astronomical units (AU, or Earth-sun units of distance). But when it comes nearest the Earth and sun, in late 2022 and early 2023, the comet should become easily visible in binoculars.

Astronomers call this comet C/2022 E3 (ZTF). It got its name because it was the third such object to be discovered in the fifth half-month (a, b, c, d, E) of this year. The ZTF stands for the Zwicky Transient Facility, which uses the 48-inch Samuel Oschin robotic telescope, located at Mt. Palomar in southern California. 

The discoverers announced Comet C/2022 E3 (ZTF) in Central Bureau Electronic Circular No. 5111, in which calculated orbital elements appear. The comet will reach its closest point to the sun, its perihelion, on January 13, 2023. At that time, it will be 1.11 AU (1.11 Earth-sun units of distance) from the sun. 

The comet will reach its closest point to the Earth, 0.29 AU or 27 million miles (44 million km), on February 2, 2023. It isn’t yet known if this comet has visited the inner solar system in the past. Astronomers must make more observations and calculations to determine that. 

The tilt of the orbit to our path around the sun is steep and retrograde, meaning the comet goes around the sun in the opposite direction than do the planets. 

This means it will, at some point, move quickly through our sky. 

Finally, the comet enters our solar system from the north, and on February 12, passes to the south of our orbital plane. This means Northern Hemisphere observers will have the better view until then, and after that the Southern Hemisphere is favored.

The discovery story

Comet C/2022 E3 (ZTF) was in the morning sky, in the direction of the constellation Aquila the Eagle, when astronomers with the Zwicky Transient Facility first spotted it. 

The ZTF program images the whole Northern Hemisphere every two nights looking for supernovae, variable stars, binary stars, flashing merging neutron stars, asteroids, and comets. It has discovered 10 comets in the past three years, and half of them carry the acronym ZTF in their names. One, discovered a year ago, was named C/2021 E3 (ZTF). Similar name, but don’t confuse the two comets. Today, we are talking about the 2022 one!

At its March 2022 discovery, this comet was a very faint 17th magnitude. Initially, it appeared as a stellar object, that is, as a dimly shining point. But, unlike the stars, whose distances make their motions undetectable except via special techniques, this object was moving in front of the stars.

Newly discovered objects that are found to be moving go into the Minor Planet Center’s NEO Page. That’s how other astronomers know to image and hopefully thereby confirm the object. As both professional and amateur astronomers do find the new object, and submit more positions for it to the Minor Planet Center, a preliminary orbit can be determined. In the case of this object, it looked more like a comet orbit than an asteroid’s orbit. That is, the path around the sun was oblong and not circular. 

At that point, the object went on the Possible Comet Confirmation Page, which begged for astronomers to image it to see if it had a coma or extended atmosphere, surrounding the object’s nucleus or core. Why is that important? It’s important because virtually all asteroids – which tend to be rocky or metallic – appear starlike (the name asteroid means “starlike”). But an icy comet will form a halo, or coma, around its nucleus as the material on the nucleus heats up when the comet is moving inward toward the sun. Only several high-magnification images, stacked to increase contrast, will show the coma of a faint comet.

Three teams imaged this new object, and they did find a coma. 

View larger. | The comet’s orbit with respect to the terrestrial worlds in our solar system – Mercury, Venus, Earth, Mars – on March 25, 2023. An interactive map of the comet’s orbit can be found at Astro.vanbuitenen.nl.
The path in our sky of comet C/2022 E3 (ZTF) through its perihelion (closest point to the sun) on January 13, 2023.

What path will C/2022 E3 (ZTF) take through our sky?

Comet C/2022 E3 (ZTF) has favorable geometry with respect to the earth.  Normally a comet will pass near the sun’s vicinity, and the elongation, which is the angle in degrees between the sun and the comet as seen from Earth, grows small and the comet disappears in the sun’s glare for a few weeks.  Not this one!  It stays in the dark sky for most of its trip through the inner solar system, even when it passes from the evening sky to the morning sky at 44 degrees north of the sun on November 21.

Northern Hemisphere observers will have a view of the comet until the end of April 2023, when the comet, then a telescopic object, will disappear into the evening twilight.

Southern Hemisphere observers will have a good view of the comet until early October when it will disappear into their evening twilight as it rapidly heads northward.  They will get their next view of the comet in early February 2023, when it pops above their northern horizon.

Many grand photo opportunities

Comet 2022 E3 (ZTF) will pass only a degree from M27, the Dumbbell Nebula, on May 31, 2022. The comet will approach to within 1/4 degree of the double star Albireo in the constellation Cygnus on June 17. 

A week later it’ll pass 1/4 degree from the globular cluster M56. And, on July 4, it’ll pass 1/2 degree from the Ring Nebula (M57). 

During this time, the comet will be faint, about magnitude 13, but imagers should be able to pick up the comet. By the time it passes 2.5 degrees south of the Hercules Globular Cluster (M13), on August 23, it will be heading south into the constellation Corona Borealis.  From here it makes a U-turn, then it heads rapidly north.  When expected to be at its brightest in late January 2023, the comet will be high in the evening northern sky in the area where the constellation Auriga is located.

The path in our sky of comet C/2022 E3 (ZTF) after its perihelion (closest point to the sun) on January 13, 2023.

How bright will the new comet get?

The path of the comet is well-determined, so we know where the comet will be in our sky.  As for brightness, comets are unpredictable.  As the nucleus warms up, it will often do so unevenly, and the brightness over time can change without warning.  Having said that, what would the average comet do?  At this point, that is the best we can do in predicting the brightness, or magnitude, of the comet.

Below is a graph showing the potential light curve for the comet.  Along the bottom of the graph is the date, while along the side of the graph we find the magnitude.  The smaller the number the brighter the object’s magnitude.  To be seen with the unaided eye a comet has to reach about magnitude 5, to be visible in binoculars it has to reach magnitude 9.

As we can see from this graph, the comet will be visible in many amateurs’ telescopes in September, as it reaches magnitude 12.  At that time, the comet will be in the northern evening sky, in the part of the sky where the constellation Hercules is located.  By mid-December, the comet will become visible in binoculars.  Observers can see the comet in the morning sky, located in the part of the sky where the constellation Corona Borealis is located.

At its brightest, the comet may attain visibility to the unaided eye in late January 2023.

View larger. | A prediction of the projected brightness of Comet C/2022 E3 (ZTF). Image via Gideon van Buitenen.

Bottom line: New comet 2022 E3 (ZTF) is headed toward the inner solar system. In early 2023, it should be easily visible in binoculars as it graces our skies. Check back with EarthSky for updates as the comet approaches its perihelion. 

Submit your comet images to EarthSky Community Photos.

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