Here's how to find the 'green comet' in the night sky before it disappears

You won't get another chance, as the comet C/2022 E3 (Z.T.F.) last flew near Earth 50,000 years ago.
Chris Young
Comet C2022 E3 (ZTF)
Comet C2022 E3 (ZTF)


A green comet called C/2022 E3 (ZTF) will make its closest approach to Earth in 50,000 years tomorrow, on February 2. The comet will come within 26.4 million miles of the planet — 110 times the distance to the moon.

The last time it flew by Earth, Neanderthals were still roaming the Earth. Astronomers believe this month's close pass will likely be the last time the comet flies past Earth, as it will soon escape the Sun's orbit.

Here is some information on the comet, including how you can observe it yourself before it leaves our region of space for good.

When was the green comet first observed?

The green comet was discovered on March 2, 2022, by astronomers Frank Masci and Bryce Bolin. They used the Zwicky Transient Facility’s wide-field survey camera at the Palomar Observatory in San Diego County, California, to make the discovery. At the time of the detection, the comet flew near Jupiter, roughly 400 million miles (643 million km) from our Sun.

The comet's name, C/2022 E3 (ZTF), reflects the date on which it was discovered and the telescope used to make the discovery.

Why is the comet green?

On January 12, C/2022 E3 (ZTF) reached perihelion, meaning it made its closest approach to the Sun. As it approached the Sun, the space rock heated to the point its ice started sublimating into gas — meaning it suddenly became so hot it skipped the liquid state. This process creates a coma around comets. A coma is essentially a nebulous envelope that surrounds a space rock.

In the case of C/2022 E3 (ZTF), the comet contains diatomic carbon, which absorbs ultraviolet light from the Sun. The resulting reaction emits green light, while the comet's envelope causes the comet's light to glow over a wider area.

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Why hasn't the green comet been seen for 50,000 years?

C/2022 E3 (ZTF) has an incredibly long-period orbit, meaning it has been traveling through the solar system's outer reaches for thousands of years.

As points out, C/2022 E3 (ZTF) appears to have a parabolic orbit, also called an escape orbit. In other words, the green comet is traveling at a high enough speed that, once it makes its way around the Sun, it will likely fly off into deep space. Its speed and trajectory will allow it to escape our Solar System's gravitational pull and never be seen near Earth again.

How can I observe the green comet?

C/2022 E3 (ZTF) is well positioned near the North Star, meaning it will likely be viewable for most of the night for stargazers looking from the northern hemisphere.

The only thing that could, unfortunately, stop you from seeing the comet in the night sky is light pollution. There will also be a full moon on February 5, meaning it's best to look for C/2022 E3 (ZTF) before that point, as the light from the moon could make it harder to spot the comet.

If you do have a dark enough sky, though, the comet should be viewable near the constellation Auriga and the star Polaris, also known as the North Star, as well as Ursa Major, which is also known as the Great Bear.

Depending on conditions, it could be viewable with the naked eye, but it's best to look for C/2022 E3 (ZTF) using a pair of binoculars or a telescope.

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