People in Japan can soon view ‘once-in-a-lifetime’ comet

Comet Tsuchinshan-ATLAS with a long tail in the morning glow is seen from Noto, Ishikawa Prefecture, on Oct. 1, 2024, in this 2.5-second exposure photo.

The first bright comet since 2020 that can be seen in the western night sky in mid-October has attracted the attention of many astronomy enthusiasts, as it is expected to be a once-in-a-lifetime encounter.

Comet Tsuchinshan-ATLAS (C/2023 A3) was observable in the eastern sky before sunrise from late September to early October. It temporarily disappeared from view, but from around Oct. 12, it will appear in the western sky after sunset. Observation conditions will improve through about Oct. 20, and a beautiful sight is expected to be seen.

The comet was discovered in January 2023 by the Purple Mountain Observatory in China and the South African telescope of the Asteroid Terrestrial-impact Last Alert System (ATLAS).

It is believed to have come from the “Oort cloud,” an area of small celestial bodies surrounding the outer solar system. This is the first time it has approached the sun, and it is thought never to return.

Since it was discovered around the middle of the orbits of Jupiter and Saturn, it was expected to become a large comet. However, it temporarily stopped brightening around June, and there was a time when it was speculated that the comet was going to disappear.

However, the comet has become brighter again since mid-September as it approached the sun. Its tail rapidly extended, and the comet took on a spectacular shape.

Along with “Comet Neowise” in 2020, this is the brightest comet with a long tail seen in Japan this century.

Comet Tsuchinshan-ATLAS was difficult to see with the naked eye between September and early October because it was low in the sky just before dawn, but from Oct. 12 onward, it will move significantly in the western sky and will become easier to find as its altitude increases day by day.

The positions of Comet Tsuchinshan-ATLAS in the western sky one hour after sunset in Tokyo between Oct. 12 and 26 are seen in this image provided by the National Astronomical Observatory of Japan. The positions will not be much different in other regions.

The National Astronomical Observatory of Japan estimates that the comet’s brightness will be at about magnitude 1.5 to 3 through Oct. 15, at magnitude 2 to 3.5 from Oct. 16 to 18, and at magnitude 2.5 to 4 on Oct. 19 and 20.

While the best time to observe it is during the few days from Oct. 16, when it will be at higher altitudes, the best period will be affected by moonlight as Oct. 17 is a full moon. It will be easier to observe with binoculars.

The brightness of comets is difficult to predict accurately and may not turn out as expected, but it will be the first bright comet seen in Japan in a while, so let’s try to see this once-in-a-lifetime comet.