Right now, south of the equator, amateur astronomers are watching a comet that’s just emerged from behind the sun. Soon, it will be the turn of observers in the Northern Hemisphere, but will Comet A3 — also known as C/2023 A3 (Tsuchinshan-ATLAS) — really become one of the brightest comets visible in the Northern Hemisphere in the last 100 years, as claimed by Star Walk? Or even potentially visible in daylight during October, as Sky & Telescope suggests?
It’s too early to tell, but we’ll soon get more clues when it becomes visible from the Northern Hemisphere later this week.
How Bright Will Comet A3 Become?
The hype is real. SpaceWeather.com reports that Comet Tsuchinshan-ATLAS is brightening rapidly, quoting Australian astrophotographer Michael Mattiazzo, who has been imaging the icy snowball before sunrise. It’s estimated to be shining at magnitude +4, which puts it within the grasp of the naked human eye. Some say it might get as bright as magnitude +0.6 (the same as bright star Vega).
“Prospects remain excellent for a visually impressive evening display in mid-October,” Qicheng Zhang at Lowell Observatory in Flagstaff, Airzxona, told SpaceWeather.com. “Weather permitting, the entire Northern Hemisphere should be able to see Comet Tsuchinshan-ATLAS.”
Given that Comet A3 had been predicted by one scientist to be on the cusp of disintegration, this is all positive news, though there is one hurdle for it to overcome if it’s to become a naked eye object for those in the Northern Hemisphere.
Why Comets Are Difficult To Predict
On Sept. 27, comet A3 will reach its perihelion — the closest it gets to the sun — at about 36 million miles (59 million km). That’s the riskiest time for a comet, which can break apart because of the sun’s influence. It’s what makes comets, and in particular their future brightness, incredibly difficult to predict.
If it does survive its journey around the sun, the period Sept. 27 through Oct. 4 will see Comet A3 shining in the east before sunrise, albeit very low on the horizon. This is best thought of as a precursor, but it will end around Oct. 4 when Comet A3 slips into the sun’s glare. If it’s bright and easily seen during that period, prepare for a spectacular show later in October when it re-emerges, with the best viewing likely on Oct. 10-20, largely because Comet A3 will get closest to Earth on Oct. 12, when it will pass about 44 million miles (71 million km) from Earth.
What The Experts Think About Comet A3
“A better bet for me, and I believe most people, is mid-October when the comet will be visible in the western sky after astrotwilight for a short period at around 4-8 degrees of elevation, depending on where you are situated,” writes astrophotographer Ollie Taylor, who took some spectacular images of Comet NEOWISE in 2020.
“The best views will probably be had post-perihelion,” writes comet expert Nick James at the British Astronomical Association. “There is a possibility that the comet will be at a negative magnitude as it emerges into the evening sky from Oct. 10 onwards.” That’s very bright.
Comet A3 is likely to have a tail of dust and ice — and possibly two tails, one whiteish and one blueish — the result of what astronomers call forward scattering. That means the comet’s orientation in the inner solar system enables its tail to reflect more light toward Earth, making it appear brighter.
How To Prepare To See Comet A3
Keep your hopes high and your expectations in check, and, just in case, pack a pair of 10×50 (or 10×42, or 15×70) binoculars, find a Dark Sky Place or identify somewhere dark using a light pollution map, and consult a sunrise and sunset calculator.
Comet A3 is a long-period comet from the Oort Cloud, a sphere around our solar system home to millions of comets, and it’s in an orbit of roughly 80,000 years. It was first discovered at over seven Earth-sun distances by astronomers at China’s Purple Mountain Observatory in January 2023 and later re-found by the Asteroid TerrestrialImpact Last Alert System (ATLAS) search station in Sutherland, South Africa, in February 2023.
Wishing you clear skies and wide eyes.
