The green comet: Comet 2022 E3 ZTF

This graphic shows the orbit view of green comet C/2022 E3 (ZTF). The grid lines on the ecliptic plane are separated by 1 astronomical unit (AU)—the average distance between the Sun and Earth, or 93 million miles (150 million km). The culms from the comet to the plane of the ecliptic are 1 month apart. Incidentally, the ram’s horn symbol beneath Jupiter marks the direction of the vernal equinox. Image via Guy Ottewell. Used with permission.

Originally posted on Guy Ottewell’s blog on January 15, 2023. Reprinted with permission.

Comet 2022 E3 ZTF: The green comet

You may have heard of the “green comet” C/2022 E3 ZTF. The fact is that although green is in the middle of the visible spectrum, it is relatively rare as an impression that astronomical objects give our eyes. Why is this comet green? This is believed to be due to a reaction of diatomic carbon (C2) molecules.

Comet has a greenish coma and a flaky tail with background stars.
Check out the photos from the EarthSky community. | Eliot Herman used a remote iTelescope from Mayhill, New Mexico to capture this image of Comet 2022 E3 ZTF on December 31, 2022. Eliot wrote: “Comet 2022 E3 on the last day of 2022. This comet is expected to be the brightest of 2023. The comet should get brighter over the next few weeks. Current weather conditions in the US are hampering observation of the comet, but hopefully there will be clear skies soon.” Thanks Eliot!

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The orbit of comet 2022 E3 ZTF

Here is my rendering of its trajectory in space.

The comet is called C/2022E3 (ZTF). “C” means that it is a non-periodic comet (in an orbit longer than 200 years). “E3” means it was the third comet discovery (or recovery) in the first half of March. “ZTF” is his “name”; It was a spin-off from the Zwicky Transient Facility (ZTF), a program to take wide-field images of the sky with a camera attached to a telescope at Palomar Observatory in California. The astronomers who noticed the faint magnitude 17 comet were Bryce Bolin and Frank Masci, but in situations like this it is common to use the institution’s name.

The comet’s orbit resembles a parabola with a period of perhaps 50,000 years. It is tilted 109 degrees to the plane of the ecliptic – meaning it is nearly vertical but slightly retrograde – in the opposite direction to that of the planets. Perihelion, or the innermost point of orbit, is not far outside Earth’s orbit. A body in such an eccentric orbit spins rapidly around perihelion.

The orbit of the green comet

The following diagrams are based – according to my calculations – on orbital elements from the Minor Planet Center at Harvard (which may change slightly in the course of observations).

Diagram of constellations with borders and a gray curved line showing a comet's path.
So the comet will race across the far north of our sky from February 1 to 21, 2023. Picture by Guy Ottewell. Used with permission.
Diagram of constellations with borders and a gray curved line showing a comet's path.
So the comet will hurtle south in late February and March 2023. Picture by Guy Ottewell. Used with permission.

The history and future path of the comet

On March 2, 2022, when it was discovered, the comet was almost as far from the Sun as Jupiter; it was in Aquila, not far north of the celestial equator and low in the morning sky. On 8 July 2022 it was in opposition in Lyra. Then, on July 30, 2022, it reached a declination of about 30 degrees north in Hercules before curving back slightly to the south.

On November 10, 2022, it was in conjunction with the Sun, but far north of it, at Serpens, south of Coma Berenices. It was at perihelion in Coma Berenices on January 12, 2023 and 1.11 AU from the Sun. It lingered in Coma Berenices before appearing to take off north as Earth swung around south of it.

On January 28, 2023, it will be in opposition again far to the north in Ursa Minor. On January 30, 2023 it will be at its most northerly point, only about 9 degrees from the north celestial pole, just above Draco’s “head”.

Diagram with constellations
Here is the scene where the comet is closest to Earth on February 2, 2023 at 3:20 UTC (9:20 p.m. CST, February 1). When the green comet is closest and brightest, it will cross Camelopardalis. An arrow shows the comet’s motion from 2 days before to 2 days after its closest approach. Unfortunately, the bright waxing crescent moon is just to the left of Taurus. Look a few days earlier and later when the comet should be about that bright. Its tail, pushed outward by the radiation pressure of sunlight, may or may not be spectacular. Image via Guy Ottewell. Used with permission.

The comet comes closest to the earth

In February, the comet will fall south and be about 0.2 AU outside of Earth’s orbit; so we see it in front of us, racing straight south. We’ll be closest to it on February 1, 2023 – at 0.29 AU – and it should be brightest then, at magnitude 5. That’s comfortably in the range of the naked eye. However, brightness predictions for comets are notoriously unreliable, as they release dust and gas in erratic amounts and directions to form the cloud-like head and tail as the core’s ice (the tiny solid) is heated by the sun. At this peak, the comet will be 121 degrees from the Sun and very high in the evening sky.

On February 12, 2023 he will descend over the ecliptic in Taurus. On March 2nd it will be one AU away from us. Then, on March 3, it will descend into the southern hemisphere, having dropped to magnitude 8. On June 20, it will again be in conjunction with the Sun, far to the south of it, about 2.6 AU from it and 3.2 AU from Earth.

Conclusion: Learn more about the trajectory of the green comet – Comet 2022 E3 ZTF – from the renowned astronomer Guy Ottewell. The comet will be closest to Earth on February 2nd.

Read more: Comet 2022 E3 ZTF closest to the Sun on January 12th

Read more: Comets are icy balls of gas and dust