C/2023 A3 (Tsuchinshan-ATLAS) did not disappoint last month. After reaching a brilliant peak at magnitude -3 to -4, though it was only within a few degrees of the Sun at the time, the comet reappeared in the evening sky at around 0^th magnitude. Though it quickly faded as it moved higher in the sky, a tail up to 20 degrees in length was visually observed. Imagers also detected the predicted anti-tail. Tsuchinshan-ATLAS starts November in the evening sky at 6^th magnitude. Since it is moving away from the Earth and Sun, it will continue to fade and should be around magnitude 9 at the end of the month. 

November will be the last month to see 13P/Olbers visually as it approaches solar conjunction. Northern hemisphere observers may be able to observe short-period comet 333P/LINEAR, which may reach 10^th magnitude at the end of the month in the morning sky. While 333P/LINEAR will be a low-elevation object for southern hemisphere observers, they will have C/2024 G3 (ATLAS) to themselves. C/2024 G3 comes to perihelion in January at a close 0.09 au from the Sun. Though it will be located very close to the Sun when at its brightest, there is an outside chance that this could be a nice object from the southern hemisphere after its perihelion.

The monthly ALPO Comet News PDF can be found here. All are encouraged to join the discussion over at Cloudy Nights.

Last month, the ALPO Comets Section received 120 images and 139 magnitude estimates of 36 comets: C/2024 S1 (ATLAS), C/2024 Q3 (PANSTARRS), C/2024 G3 (ATLAS), C/2024 B1 (Lemmon), C/2023 V4 (Camarasa-Duszanowicz), C/2023 TD22 (Lemmon), C/2023 R1 (PANSTARRS), C/2023 C2 (ATLAS), C/2023 A3 (Tsuchinshan-ATLAS), C/2022 U1 (Leonard), C/2022 N2 (PANSTARRS), C/2022 E2 (ATLAS), C/2021 S3 (PANSTARRS), C/2020 V2 (ZTF), P/2024 Q2 = P/2005 SB216 (LONEOS), P/2010 WK (LINEAR), 384P/Kowalski, 360P/WISE, 328P/LONEOS-Tucker, 305P/Skiff, 253P/PANSTARRS, 229P/Gibbs, 208P/McMillan, 190P/Mueller, 154P/Brewington, 146P/Shoemaker-Levy, 136P/Mueller, 130P/McNaught-Hughes, 89P/Russell, 54P/de Vico-Swift-NEAT, 50P/Arend, 49P/Arend-Riguax, 43P/Wolf-Harrington, 37P/Forbes, 13P/Olbers, and 12P/Pons-Brooks. 

A big thanks to our recent contributors: Dan Bartlett, José J. Chambó, Dan Crowson, Michel Deconinck, Jose Guilherme de Souza Aguiar, Juan Jose Gonzalez Suarez, Christian Harder, Eliot Herman, Rik Hill, Michael Jäger, John Maikner, Gianluca Masi, Michael Mattiazzo, Martin Mobberley, Mike Olason, Andrew Pearce, Chris Schur, Tenho Tuomi, and Christopher Wyatt.

The monthly ALPO Comet News PDF can be found Cloudy Nights forum. All are encouraged to join the discussion over at Cloudy Nights.

C/2023 A3 (Tsuchinshan-ATLAS) has reappeared in the morning sky for those with a low, clear eastern horizon. It was first observed from the southern hemisphere around mid-month. Now the comet is also visible to those in the northern hemisphere.

Recent observations place C/2023 A3 at magnitude 3.5 which is a few tenths of a magnitude brighter than predicted in the September ALPO Comet News. While magnitude 3.5 sound like an easy naked eye object, the big caveat is the comet doesn’t rise in the morning sky until just before the start of astronomical twilight at mid-southern latitudes and the just after the start of nautical twilight at mid-northern latitudes. As a result, the comet is at an elevation of only a few degrees above the horizon in bright twilight. So far all September observations have been reported with the help of small binoculars. Most observations are also reporting a dust tail between 0.5 and 2 degrees in length.

The comet will continue to be located low in the morning against a bright sky into early October. For southern hemisphere observers, it will be at its highest, a whopping 2 degrees above the horizon at the start of astronomical twilight, on Sept 24-26. For northern mid-latitude observers it will be at its highest on Sept 28-30 at an elevation of 3 degrees at the start of nautical twilight (when the Sun is only 12 degrees below the horizon).

Perihelion occurs on Sept 27. The comet will continue to brighten after perihelion due to a decreasing Earth-comet distance and increasing phase angle, it should be around magnitude 2.5 by Sept 29-30. If your horizon allows you to see the comet now (Sept 23-24), you should be able to follow it as it falls back into the glare of the Sun through October 3-4 when the comet will have brightened to around magnitude 1.0. 

Though we will lose sight of the comet in early October, it will only be for a few days. Will post another update before then.

The stage is set for C/2023 A3 (Tsuchinshan-ATLAS), which will arrive at the perihelion on September 27. In August, the comet continued to brighten slowly, but otherwise, it looked healthy. The STEREO-A spacecraft took the last observations on August 21, with the comet now too close to the Sun to be observed.

Assuming the comet continues to brighten and not disintegrate, it should become observable again during the second half of September, at least for those clear, unobstructed eastern morning horizons. The comet will be competing with a rapidly brightening dawn sky. It should be within range of imagers, but will it be bright enough for visual observations?

The real show will be in October, when the comet may become a short-lived daylight comet from October 8 to 10 and then a nice evening object starting around October 13.

Two other comets are expected to be brighter than 12^th magnitude in September. 13P/Olbers is a northern hemisphere object fading from 8^th to 9^th magnitude in the evening sky. 12P/Pons-Brooks is a southern hemisphere object fading from 10-11^th magnitude, also in the evening sky.

Last month, the ALPO Comets Section received 103 images and 167 magnitude estimates of 22 comets: C/2023 V4 (Camarasa-Duszanowicz), C/2023 C2 (ATLAS), C/2023 A3 (Tsuchinshan-ATLAS), C/2022 N2 (PANSTARRS), C/2021 S3 (PANSTARRS), C/2021 G2 (ATLAS), C/2020 V2 (ZTF), C/2020 K1 (PANSTARRS), P/2010 WK (LINEAR), 328P/LONEOS-Tucker, 305P/Skiff, 302P/Lemmon-PANSTARRS, 146P/Shoemaker-Levy, 136P/Mueller, 133P/Elst-Pizarro, 130P/McNaught-Hughes, 125P/Spacewatch, 89P/Russell, 54P/de Vico-Swift-NEAT, 37P/Forbes, 13P/Olbers, and 12P/Pons-Brooks.

A big thanks to our recent contributors: Dan Bartlett, José J. Chambó, Michel Deconinck, Jose Guilherme de Souza Aguiar, Juan Jose Gonzalez Suarez, Christian Harder, Eliot Herman, Michael Jäger, John Maikner, Gianluca Masi, Michael Mattiazzo, Martin Mobberley, Mike Olason, Andrew Pearce, Chris Schur, and Christopher Wyatt.

The monthly ALPO Comet News PDF can be found here. A shorter version of this report is posted on a dedicated Cloudy Nights forum. All are encouraged to join the discussion over at Cloudy Nights.