Earth’s sky is about to gain a bright object, one that could briefly rival the North Star in visibility—if it doesn’t melt first.
China’s Tsuchinshan Observatory discovered Comet C/2023 A3 (Tsuchinan-Atlas) in January 2023, with the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in South Africa spotting it again a few weeks later. Since then, scientists and amateur astronomers around the world have been watching it through telescopes, but those instruments likely won’t be necessary when it reaches its closest point to Earth on October 12. On that date, it’s possible that Comet A3, as it’s known for the sake of brevity, will become the brightest comet of the year.
On September 27, A3 will reach its perihelion, the point in its orbit at which it passes closest to the Sun. When it does, it will be less than half the distance of Earth to the Sun. A few weeks later, it will reach its closest distance to our planet.
There are a few dates for stargazers to pencil into their calendars should they wish to catch a glimpse of Comet A3. According to telescope manufacturer Celestron, the comet will have a magnitude of 3.4 as it reaches its perihelion, and may be visible to the unaided human eye. It will be even brighter once it reaches its closest point to Earth, with a possible magnitude of 1.9. Using data from the British Astronomical Association, In the Sky has predicted a magnitude of 2.8.
Magnitude works on a scale in which the lower the number, the brighter the object. For reference, the North Star generally has a magnitude between 1.98 and 2.02, while the Sun’s magnitude is -26.74. The comet will not come this close to Earth again for another 80,000 years or so, so get a peek while the feeling’s good.
To get the best view, you’ll want to get away from the light pollution of cities and find a remote location. Allow some time for your eyes to adjust to the dark. A good pair of binoculars or a telescope will offer the optimal view, but to make the best of your bare peepers, Celestron advised against staring straight at A3. Instead, turn your head about 20 degrees away from it, which will allow the most sensitive parts of your eyes to pick up the light bouncing off A3. The comet should appear streaking through the Virgo constellation. Stargazing apps such as Sky Guide can help you locate the constellation and the comet itself.
Comet A3 has exhibited some unusual behavior related to its magnitude. The SETI Institute has been keepings its eye on the celestial object via its citizen scientist Unistellar Network initiative. Observations by amateur astronomers indicated that Comet A3 unexpectedly dimmed in April and May 2024 before getting brighter again. The comet’s brightness dimmed even though it was moving closer to the Sun. According to SETI, the dimming may have been because of the comet’s angle relative to the Sun and Earth, which caused less of the star’s light to reflect towards our planet.
Unfortunately for the comet, and for stargazers, there is another possible reason for the comet’s shrinking light signature. Comets are largely made up of dust and ice, and Comet A3 could be gradually breaking apart as it nears the Sun—a scenario that seems especially likely given that A3 will pass even closer to the Sun than Mercury. If that’s the case, A3 may lose all of its ice, which should appear as a bright envelope as it turns to gas, by the time it’s closest to Earth.
So keep your fingers crossed and hope that A3 thinks Neil Young is a liar. When you enjoy staring into the black night sky to catch a glimpse of comets, it is not, in fact, better for them to burn out than fade away.
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