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.
Now available! 2023 EarthSky lunar calendar. A unique and beautiful poster sized calendar showing the moon phases every night of the year! And it’s a great gift.
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).
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”.
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
