Famend British astronomer Man Ottewell originally published this piece about Comet C/2021 T4 Lemmon on May 25, 2023. Reprinted with permission. Edits by EarthSky.
Comet C/2021 T4 Lemmon
Comet C/2021 T4 Lemmon was found on October 7, 2021, on photographs taken on the Mount Lemmon Observatory, northeast of Tucson in Arizona. T4 means the 4th discovery or restoration within the first half of October.
Mount Lemmon is the very best level of the Santa Catalina Mountains, one in all 4 mountain ranges round Tucson. It’s to not be confused with Catilina, the conspirator who tried to grab energy over the Roman republic in 63 BC. I’m reminded of my hypothesis that the Navajos might have seen Canopus, the good star of the south, from one of many 4 sacred peaks surrounding their land. The truth is, it’s proven as the duvet image for the Astronomical Calendar 2023.
When found, comet C/2021 T4, due to the geometry of its orbit, appeared fairly northerly, at declination +12°.
Comet C/2021 T4 Lemmon is a protracted interval comet
The truth is, it’s a long-period comet; if it ever beforehand dropped from its distant residence – at 44,000 AU out – to the inside solar system, it could have been thousands and thousands of years in the past. So throughout its current passage, it’ll really feel gravitational perturbations from the planets that may shorten its interval to merely hundreds of years.
Its orbit is inclined about 20° to the ecliptic airplane. Nevertheless, it’s moving into a retrograde route, or reverse to the route wherein the planets revolve. The result’s that it’ll make a really lengthy fast sweep throughout our southern sky.
Finder chart
At current the comet is 60° out within the morning sky, southerly (at declination -13°), 1.75 AU from the sun and a pair of AU from Earth. Nevertheless, it’s nonetheless at a dim magnitude of about 11. Then, on June 27, 2023, its distance from us will shrink to 1 AU.
On July 18, 2023, we are going to move it at opposition. And round this time, it’ll be nearest to us, 0.54 AU, and brightest, maybe about magnitude 8 or 7 however nonetheless under the unaided-eye restrict. Its nearness will make it seem even farther south, at declination -56° on July 20.
Then within the following months it is going to climb north, changing into decrease within the night sky and extra distant. On the identical time it’ll be dimming by maybe two or three magnitudes. It is going to attain perihelion, 1.48 AU from the sun, on July 31, 2023. Lastly, it’ll ascend throughout the ecliptic on September 10, 2023; and be at conjunction behind and north of the sun on November 9, 2023.
After all, we should do not forget that predictions of a comets’ brightness, and the dimensions of their tails, may be unreliable. That’s as a result of they rely on the melting of ice and launch of dust in these lumpy spinning objects.
Comet-Hale Bopp nonetheless observable? Wow!
By the best way, Alan Hale alerted us (Man Ottewell) to this comet with a Fb submit on Could 22. Alan was discoverer of the good comet Hale-Bopp (C/1995 O1)). And, regardless of now being greater than 47 AU away, it’s the primary on the Minor Planet Center’s listing of at present observable comets, not due to its current magnitude (about 20) however as a result of it’s the earliest-numbered non-periodic comet nonetheless thought-about observable in any respect.
Backside line: Comet C/2021 T4 Lemmon was found from Mount Lemmon Observatory in 2021. It’s at present sweeping via the southern skies.
