'Once-in-60,000-years' comet expected to light up night skies in October

A rare comet that was identified last year will make its first close pass by Earth in mid-October, according to NASA.

Astronomy enthusiasts already spotted the comet coded C/2023 A3 in late September as it made its closest approach to the sun. The comet is expected to be at its nearest to Earth around October 12, when it will appear in the western sky of the Northern Hemisphere after sunset, offering stargazers another opportunity to observe.

What's a comet?

A comet is a celestial object composed of ice, dust and other volatile materials. When comets approach the sun, the solar radiation causes the volatile materials on their surface to sublimate, releasing gas and carrying dust, which forms the comet's coma and tail.

The C/2023 A3 comet was first discovered by the Xuyi Observation Station of the Purple Mountain Observatory (PMO), Chinese Academy of Sciences, on January 9, 2023. It was later confirmed by the International Astronomical Union's Minor Planet Center and named Tsuchinshan-ATLAS.

Also known as C/2023 A3, the letter "C" indicates a comet that takes more than 200 years to finish an orbit around the sun, the number "2023" represents the year it was discovered, while "A" denotes the first half of January, and "3" means it was the third object discovered in the first half of the month.

"After a period of observation, we determined its orbit, and based on the shape of the orbit, we calculated that its orbital period is approximately 60,000 years," Zhao Haibin, researcher at PMO, told the Beijing News.

Zhao added that with the increase in observational data and non-gravitational effects, the comet's orbit may change slightly.

When to see the comet?

Experts suggest that there is a high chance that stargazers will be able to see the comet with the naked eye.

For viewers in the Northern Hemisphere, the comet will appear shortly after sunset on October 12, in the low western sky in the constellation Virgo. However, the window for naked-eye observation will be brief, about 10 to 20 minutes, Wang Kechao at PMO told China Media Group (CMG).

In the following days, as the comet's angular distance from the sun increases, it will become easier to see with the naked eye, entering its optimal viewing period, said Wang. "About an hour after sunset, it will be visible in the western sky."

In late October, although the comet's brightness will begin to fade, its increasing angular distance from the sun will extend the time available for observation. The public will have two to three hours of viewing time after dark, Wang said.

Due to the comet's parabolic orbit, its brightness will gradually decrease as it moves farther from the sun and Earth, Wang explained. "Based on current predictions, it will become difficult to see with the naked eye around November."

"Naked-eye-visible comets are rare enough as it is, and this one has the potential to be amongst the brightest that we've seen in the last few decades. So it's certainly worth a go," Gregory Brown, senior public astronomy officer at the Royal Observatory Greenwich, told the Guardian.