Tootfinder

A 7-mag. #comet with a 3° tail nobody saw coming is grazing southern skies today: "SWAN 25B" (preliminary name) was discovered by amateurs in spacecraft images and seems to be in its 0.5 au perihelion today. Whether it's undergoing an outburst or will stay bright remains TBD: here's an image from Chile while a lot of discussion can be found in the threads https://groups.io/g/comets-ml/topic/115202009 and https://groups.io/g/comets-ml/topic/115202920

First the nucleus of #comet SWAN split - https://skyweek.wordpress.com/2025/11/02/allgemeines-live-blog-ab-dem-2-november-2025/#Nov06 ("Der Kern des Kometen C/2025 R2 (SWAN) ist zerbrochen ...") - and now C/2025 K1 (ATLAS) has suffered the same fate: a 2-meter-telescope image from https://www.astronomerstelegram.org/?read=17487 ("Multiple Fragmentation Observed"), also https://groups.io/g/comets-ml/topic/116216567 (several amateur observations) and https://www.astronomerstelegram.org/?read=17488 (Hubble detections of more fragments, sadly no pictures included).

Der #Comet-Browser von #Perplexity wirkt wie ein Stern am KI-Himmel – leuchtet aber eher schwach, wenn es um den Umgang mit hochgeladenen Dateien geht. Räume sichtbar, Inhalte unzugänglich. Bis zur technischen Gleichwertigkeit mit der Webversion bleibt der Browser ein Versprechen mit Warteschleife.…

And here comes my #Bochum, Germany, #Lemmon number 6: today it was very clear for a change, and the #comet with quite some tail (an effect of the imminent perigee?) showed up nicely - and even faintly in binoculars - at the end of nautical twilight.

60 years ago #OTD (or tomorrow) #comet #IkeyaSeki showed a dramatic tail: https://solarviews.com/cap/comet/ikeya.htm - and this chemical 'raw' picture proves it beyond doubt ... while nowadays creepy 'astrophotographers' past high-end stacks of the faint tails of comet Lemmon into landscape pictures creating similar "photographs" which then get likes galore. Sigh ...

Comet C/2025 A6 (Lemmon) is doing very well already, months before its perihelion - and it's not a transient outburst: "To measure the total brightness, the entire coma of 7' was used in Astrometrica," writes Michael Jäger in #comet *could* thus reach 2nd or 1st magnitude in late October / early November when it's observable in Ser, Her and Oph at a solar elongation of around 35° ... unless it decides to stay dimmer, of course.

60 years ago #OTD #comet #IkeyaSeki reached perihelion, -10 mag., was visible in daylight and showed a spectacular tail in the following weeks: https://groups.io/g/comets-ml/message/32770 and https://www.astronomy.com/today-in-the-history-of-astronomy/sept-18-1965-discovery-of-comet-ikeya-seki/ and https://noirlab.edu/public/images/noao-01854/

The clouds over Bochum, Germany, cleared too late this evening, so instead of Lemmon I tried #comet C/2025 R2 (SWAN) for a change - here it is: both pictures with a bridge camera on a tripod, 5 seconds at f/2.8 and ISO 3200. It's fading: according to https://cobs.si/obs_list?id=2659 the brightness is 6.7 mag. right now.

Not only Lemmon but also #comet #SWAN has been imaged by Kimiya Yui from the #ISS: in https://x.com/Astro_Kimiya/status/1982242913389015085 it's peeking through the space station's solar arrays. (AFAIK this is a first, *two* comets getting imaged from the ISS at the same time.)

A D/H Ratio Consistent with Earth's Water in Halley-type Comet 12P from ALMA HDO Mapping: #comet, 12P/Pons-Brooks, matches Earth’s oceans, strengthening the theory that comets helped make our planet habitable.

After a complicated and one good sighting of #comet #Lemmon from #Bochum, Germany, on 20 and 24 October - see the thread https://mastodon.social/@PlanetariumBochum/115430462668539532 - more cloudy evenings followed ... but here is the comet again on 30 October, picked blindly out of a suuuuper-crappy sky with 4 seconds at f/2.8 and ISO 1600, right above 9 Herculis. Detection #3 ... and there would be one more today (see the following boost).

#Comet C/2025 R2 (SWAN) - as it's now officially called: https://minorplanetcenter.net/mpec/K25/K25RA2.html with new orbital elements - next to Spica in an image by G. Rhemann & M. Jäger remotely with a 12-inch telescope in Namibia: https://www.facebook.com/photo/?fbid=24139356712431407