How and When to See Comet A3 As It Passes By Earth (and Possibly Its Live Disintegration)

One of the most anticipated astronomical events of 2024 is fast approaching. The star of the show is Comet A3, which will light up the night sky and be visible from Earth for the first and last time.

What is Comet A3? C/2023 A3 (Tsuchinshan-ATLAS) is a non-periodic comet from the Oort cloud. Two observatories discovered it simultaneously in January 2023: the Purple Mountain Observatory in China and the ATLAS project (or Asteroid Terrestrial-impact Last Alert System) in Hawaii.

A3 follows an extremely long elliptical orbit around the Sun and spends tens of thousands of years passing through the solar system.

When can we see it? Astronomers believe the comet will be visible in October 2024 after it passes the Sun at its perihelion. It’s still too early to be sure, but experts believe it will reach a brightness of magnitude -1, which is similar to the brightest stars in the night sky.

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While the negative magnitude might be confusing, astronomy uses an inverse scale: the lower the number, the brighter the object. In this case, the magnitude of A3 is rapidly decreasing:

• March - April 2023: Brightness increases to magnitude 16.5.
• May - August 2023: Brightness stabilizes at magnitude 16.
• December 2023: Brightness rises to magnitude 14.5.
• February - March 2024: Brightness increased to magnitude 11.
• April 2024: magnitude 10.

Currently, C/2023 A3 is visible with small telescopes and has a 2.5 arcminute tail.

How can we see it? The key days for observing the comet will be October 12 and 13, which is when astronomers expect its brightness to peak after its perihelion on September 27.

In the northern hemisphere, people will be able to see it after sunset in the constellation of Virgo or with the help of a star-mapping app. People living in the southern hemisphere will have a tougher time observing A3 on these dates. However, they should be able see it in the morning sky starting in September.

Unless... The great unknown with comet A3 is whether it will survive its passage near the Sun. Some astronomers predict that we'll see a spectacle as bright as the famous Hale-Bopp in 1997. Others believe A3 will disintegrate at its perihelion in late September.

Either way, the show promises to be spectacular, so we recommend looking for a place away from the light pollution of the city with a clear horizon.

Image | Comet Hale-Bopp in 1997 (NASA)