Tootfinder

Whoa, what has the #Kreutz comet C/2026 A1 (MAPS) done now?!? Photometry from images by the outer corona observing satellite constellation PUNCH - by Thomas Lehmann; https://groups.io/g/comets-ml/message/35106 - shows a sudden increase in coma brightness ... whatever that means for the apparently quite fragile nucleus. PUNCH can follow the comet closer to the Sun than ground-based observers who will lose sight by month's end.

Two attempts to simply extrapolate the brightness of #Kreutz comet C/2026 A1 (MAPS) from what happened in the past few weeks, from all visual observations reported to COBS (left) and from all CCD observations of the past month which would have the brightness climb a bit faster. But as the previous post in the thread has shown even in the geometrically preferred southern hemisphere MAPS is lost in twilight from about March 30 to April 7 - and even in the optimistic model the comet has reached only 6th magnitude when it is lost and is down again to 5th when it is recovered: unless something drastic would happen *all* hope for an interesting show rests on a possible post-perihelion dust tail. Good luck ...

The uncertain brightness and tail(s) development of #Kreutz #comet C/2026 A1 (MAPS) is one thing - see the curves in https://astro.vanbuitenen.nl/comet/2026A1 and https://aerith.net/comet/catalog/2026A1/2026A1.html for guesses and https://cobs.si/obs_list?id=2688 for the current value which is ~8.5 mag. - but the viewing geometry is the other: here it is for 51.5° North (my place Bochum) and 22.5° South (Windhoek) as the view is much better from the southern hemisphere.
The table first gives the elongation (angle between comet and Sun in the sky) and the phase angle (the angle Sun - comet - Earth) which nearing 180° can lead to significant boost of brightness by forward scattering on dust.
And this is followed by the altitude of the comet at the solar depressions given in the top line, for Bochum and Windhoek: sunset and end of civilian twilight and for the latter also the end of nautical and astronomical twilight, i.e. the onset of night. Also of importance is the angle of a hypothetical dust tail (simulated in https://hdr-astrophotography.com) after perihelion, also much better in the South: https://britastro.org/section_news_item/c-2026-a1-maps-a-kreutz-group-sungrazer - but first MAPS has to survive the latter *and* release a lot of dust at the right time ...

Preliminary Nucleus Size Estimate for #Kreutz Sungrazer C/2026 A1 (MAPS): https://iopscience.iop.org/article/10.3847/2515-5172/ae5220 -> "JWST imagery of the approaching Kreutz sungrazer C/2026 A1 (MAPS) appears sufficient to distinguish the comet’s nucleus from the surrounding dust. Coma model fitting indicates the morphology is compatible with a ∼0.4 km diameter nucleus—likely larger than those of the minor Kreutz fragments routinely discovered with coronagraphs, and comparable to or slightly smaller than that of C/2011 W3 (Lovejoy). However, since C/2026 A1 is the only Kreutz sungrazer whose nucleus has been directly observed, these comparisons should be treated with caution" -> https://groups.io/g/comets-ml/message/35035 / https://scicomm.xyz/@qicheng@cometary.org/116245251072721081

Whatever eagerly awaited #Kreutz #comet C/2026 A1 (MAPS) is up to - see also https://groups.io/g/comets-ml/topic/118409957 and https://nitter.net/JAtanackov/status/2035718257060036738 and https://scicomm.xyz/@qicheng@cometary.org/116262858373488354 - less than two weeks from perihelion, it has developed a long plasma tail now: https://www.facebook.com/photo/?fbid=25816609931372735 (Rhemann & Jäger yesterday with a 12 inch telescope; full and detail).

"The most recent orbital computations make it increasingly likely that the object [the new #Kreutz comet MAPS] is a fragment of one of the comets observed by Ammianus Marcellinus in AD 363, thereby strengthening evidence in support of the contact-binary hypothesis of the Kreutz system," writes Zdenek Sekanina in https://arxiv.org/abs/2602.17626: "In this context, the comet is the only second-generation fragment of Aristotle's comet that we are aware of to appear after the 12th century. It does not look like a major fragment, but rather like an outlying fragment of a much larger sungrazer."

Will THIS become the comet of the year if not decade? "6AC4721" doesn't even have a proper number or name but it is on a #Kreutz orbit that will bring it very close to the Sun in April - and was discovered already farther from the Sun than even Ikeya-Seki, whatever that means: https://www.facebook.com/groups/227002358661288/posts/1665380981490078/ and https://astronomynow.com/2026/01/16/potentially-bright-sungrazing-comet-discovered/ and https://x.com/JAtanackov/status/2012283238807482804 discuss the uncertain outcome of the adventure. In any case here is the comet last night: "Kreutz Comet 6AC4721 is currently brighter than expected,." write G. Rhemann and M. Jäger: "A deeper image from Namibia (Jan 16.91, 12“/3.6 12x120sec with Asi 6200) already shows a 2' coma and 85” coma in Pa 41. The total brightness measured with the Tycho Tracker was 16m5."

So the new #Kreutz #comet #MAPS is *still* following the constant rapid rise in brightness it has shown since discovery: a dumb extrapolation - https://cobs.si/analysis/?comet=2688&from_date=2026-01-15 00:00&to_date=2026-04-30 00:00&observation_type=V&observation_type=C&plot_x_value=1&plot_y_value=1&fit_option=1&exclude_faint=on&exclude_issue=on&observer=&association=&country=&compare_values=compare - has it get 10,000-times brighter than the Sun at its extremely close perihelion which makes so sense at all, of course, physically.
"It must therefore be assumed that this increase in activity will level off significantly in the near future," writes https://fg-kometen.vdsastro.de/koj_2026/c2026a1/26a1eaus.htm: "More likely are parameters m m0=12.0 mag / n=4 (or even lower), which would still result in a (very short-term) maximum brightness of about –9 mag (but this would probably still be significantly too bright) – always assuming that the comet survives its perihelion passage unscathed."
For other views see http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET005663.txt and https://arxiv.org/abs/2602.17626 and https://www.facebook.com/photo?fbid=10236580364221799 and https://cometografia.es/cometa-kreutz-2026-a1-maps-analisis/ - and the actual brightness is tracked at https://cobs.si/obs_list?id=2688 where it has reached ~11.5 mag. now.

The #Kreutz #comet #MAPS "has become more than 1 mag brighter between March 6 and 9" and stands at 10.5 mag. right now: https://groups.io/g/comets-ml/message/35019 and https://www.facebook.com/photo/?fbid=2374472359736249 with the latest picture by Jäger & Rhemann here - less than 4 weeks til perihelion, and the brightness continues to rise with a strong n~8 ...

The new #Kreutz #comet discovered unusually early has been named C/2026 A1 (MAPS): #photosphere on 4 April and becoming a bright comet.

The new #Kreutz #comet is now C/2026 A1 (MAPS): http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET005658.txt and #perihelion is highly uncertain but there is hope as https://www.facebook.com/groups/227002358661288/posts/1670699484291561 and https://groups.io/g/comets-ml/topic/117373975#msg34667 explain. And if MAPS makes it to perihelion and is (very) bright then coronagraphs on the ground might be able to catch it against the inner corona as the following table - calculated with https://ssd.jpl.nasa.gov/horizons/app.html#/ - shows.