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.

This month’s ALPO Comet News will be another short one. Again, other commitments are vying for my time, and only four comets are expected to be brighter than magnitude 12 this month.

Northern hemisphere observers will be able to watch two fading comets, 13P/Olbers fade from 7th to 8th magnitude and C/2023 V4 (Camarasa-Duszanowicz) from 11th to 13th. Southern hemisphere observers will be able to observe 12P/Pons-Brooks fade from 9th to 10th magnitude. Southern observers will also be able to catch C/2023 A3 (Tsuchinshan-ATLAS) brighten from 8th to 7th magnitude before losing it to the glare of twilight around mid-month.

Last month, the ALPO Comets Section received 247 images and 164 magnitude estimates of 44 comets: 12P/Pons-Brooks, 13P/Olbers, 21P/Giacobini-Zinner, 29P/Schwassmann-Wachmann, 32P/Comas Sola, 37P/Forbes, 62P/Tsuchinshan, 65P/Gunn, 89P/Russell, 125P/Spacewatch, 130P/McNaught-Hughes, 144P/Kushida, 146P/Shoemaker-LINEAR, 154P/Brewington, 208P/McMillan, 227P/Catalina-LINEAR, 236P/LINEAR, 251P/LINEAR, 253P/PANSTARRS, 299P/Catalina-PANSTARRS, 468P/Siding Spring, C/2017 K2 (PANSTARRS), C/2019 O3 (Palomar), C/2019 T4 (ATLAS), C/2019 U5 (PANSTARRS), C/2020 K1 (PANSTARRS), C/2020 V2 (ZTF), C/2021 G2 (ATLAS), C/2021 S3 (PANSTARRS), C/2021 X1 (Maury-Attard), C/2022 E2 (ATLAS), C/2022 L2 (ATLAS), C/2022 N2 (PANSTARRS), C/2022 U1 (Leonard), C/2023 A3 (Tsuchinshan-ATLAS), C/2023 C2 (ATLAS), C/2023 V4 (Camarasa-Duszanowicz), C/2023 X1 (Leonard), C/2024 A2 (ATLAS), C/2024 C4 (ATLAS), C/2024 E1 (Wierzchos), C/2024 F2 (PANSTARRS), C/2024 G1 (Wierzchos), C/2024 G3 (ATLAS), and C/2024 J1 (Wierzchos).

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, Uwe Pilz, Chris Schur, Greg T. Shanos, Tenho Tuomi, 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.