Comet Tsuchinshan-ATLAS on its way for a great show in October

Comet C/2023 A3 (Tsuchinshan-ATLAS), first discovered in early 2023, has been zooming towards the inner solar system ever since. Earlier this year it was touted as potentially becoming the brightest comet in decades. Then some news came that it may have already started to 'self destruct' as it approached the sun.

August 10th with a 2.8′ coma and 16.9′ tail

Despite fears that it may be disintegrating, the comet was spotted by NASA's STEREO-A spacecraft on the other side of the sun and seems to be in good health (whatever good health means for a ball of dirty ice). I'm anticipating some good news in the next few weeks, but comets are very fickle, and they do what they want - remember comet ISON?

September 27th marks the date of perihelion, the point in the comet's orbit when it is closest to the sun. After perihelion passage C/2023 A3 will start moving away from the solar system. If it survives perihelion, it will then race upward in the western sky - prime viewing for us in the northern hemisphere. 

On October 9, 2024, C/2023 A3 will be close to the sun but may be visible if the comet turns out to be as bright as the most optimistic forecasts claim it might - as bright as Venus. Each night it gets higher and higher and will be easier to spot against the darker sky.  But it's also getting dimmer and dimmer, and any tail will start to decrease in length as the comet leaves the sun's vicinity. 

Key events:

October 10 - comet head glows brightly with an ion tail rising straight up. The dust tail should be splendid due to the forward scattering effect as it is situated between us and the sun.

October 13 - a sunward-pointing anti-tail forms, as the comet now can be seen in a darker sky about 14 degrees in altitude at 7:00pm EDT.

October 15 - Tsuchinshan-ATLAS passes close to M5, the Rose Cluster, a globular cluster of stars. In a dark sky away from the light pollution of nearby cities. Binoculars should show the pair in the same field of view.

Each night the comet moves about 3 - 4 degrees higher and to the SW. It should remain visible until the end of the month. Those with small telescopes can follow it into November.

A great simulation by Nicolaus Lefaudeux (hdr-astrophotography) shows the anticipated two apparition highlights — the growth of an approximately15° dust tail and even longer gas tail from September 28th through October 2nd. When C/2023 A3 climbs away from the Sun in the evening sky, its dust tail will stretch about 10°, with a gas tail possibly as long as 40°! Viewing circumstances at dusk are also ideal for viewing the comet's anti-tail, which may rival that of Comet Arend-Roland in 1957.

More to come as we get closer to the end of September.