After months of waiting, a comet the could prove to be bright enough to see with the naked eye and even during the day from the northern hemisphere, has arrived — and the first photos are in.
“If it survives its passage near the sun, becoming one of the brightest objects visible in the northern hemisphere — like Comet McNaught in 2007 — Comet A3 could prove to be one of the most significant celestial events of the year or even the decade,” said Franck Marchis, director of citizen science at the SETI Institute and co-founder of smart telescope maker Unistellar, which has a comet-dedicated tutorial page. “Observations will, in theory, provide answers to whether it will reach a magnitude of -2. As unpredictable as it is magnificent, it’s an event not to be missed!”
If you’re wondering how, when and where to see Comet A3 — also known as C/2023 A3 (Tsuchinshan-ATLAS) and “comet of the year”— here’s everything you need to know.
Check my feed every day this week and next for a daily “comet tracker” with sky-charts and tips for viewing Comet A3.
Comet A3: When?
Comet A3 will first reach its closest to the sun, then its closest to Earth. Both of these occasions should see it shining brightly for observers in the northern hemisphere.
- Sept. 27-Oct. 3: comet A3 will reach its perihelion — the closest it gets to the sun — at about 36 million miles (58 million km) on Sept. 27, and be visible for around a week before sunrise. During this period, comet A3 is expected to be at its dimmest, and very close to the horizon, so may be be a challenging observation, but one worth making. Binoculars are advised.
- Oct. 12-Oct.26: comet A3 will reach its closest to Earth at about 44 million miles (71 million km) from Earth on Oct. 12 and become visible after sunset, initially close to the horizon, but quickly moving away from the sun, so higher up in the sky. This is when it’s expected to be at its brightest.
Comet A3: What Time?
From Sept. 27-Oct. 3, comet A3 will be visible from mid-northern latitudes about 75 minutes before sunrise where you are. It will be best seen at this time, when it will be both highest in the sky and in the darkest skies before dawn breaks.
From Oct. 12-Oct.26, comet A3 will be positioned due west after sunset, rising higher above the horizon each evening. It will initially be visible for only a short window after after sunset where you are, but will rise higher each night, into darker skies, but will dim as it does so.
Comet A3: What Direction?
From Sept. 27-Oct. 3, comet A3 will be visible in the east-southeast direction before sunrise, sinking lower into the horizon each morning before disappearing int o the sun’s glare.
From Oct. 12-Oct.26, comet A3 will be positioned due west after sunset, rising higher above the horizon each evening.
Comet A3: Do I Need Binoculars?
Between Sept. 27 and Oct. 3, comet A3 may not be bright enough to be easily seen with the naked eye, so having a pair of binoculars to hand would be a great idea, just in case.
From Oct. 12-Oct.26, comet A3 is expected to brighten significantly and be visible to naked eyes — the sweet spot being around Oct. 13-16.
Comet A3: What Will It Look Like?
Comet A3 will appear to the naked eye as a small, fuzzy blob with a tail pointing away from the sun.
A comet is made from ice and dust. As it gets closer to the sun, it heats up slightly. That causes the ice covering its nucleus to become a gas, creating a coma. This gas — and dust — from the coma trails behind the comet, causes a tail, which can be hundreds of millions of miles long. Comet A3’s tail is about 27 degrees in length, the same as the span between your pinky finger and thumb if you hold your hand outstretched against the sky.
However, Comet A3 — as with many comets — actually has two tails. Its blue-ish plasma tail is made of ionized gas, while its other, whitish tail is made of dust.
How Close Will Comet A3 Get?
There are two points at which a comet is brightest in Earth’s sky — when it’s closest to the sun and when it’s closest to Earth. On Sept. 27, comet A3 will reach its perihelion — the closest it gets to the sun — at about 36 million miles (58 million km). That’s about the distance that Mercury orbits the sun from. Comet A3 will get closest to Earth on Oct. 12, when it will pass about 44 million miles (71 million km) from Earth.
What Is Comet A3?
Comet A3 is a long-period comet from the Oort Cloud, a sphere around our solar system home to millions of comets. It’s in an orbit of roughly 80,000 years.
It was discovered in January 2023 by astronomers at China’s Tsuchinshan Observatory and in February 2023 by South Africa’s Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope.
Wishing you clear skies and wide eyes.
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