Jorma RyskeNov 2
Qicheng Zhang
Interstellar comet 3I/ATLAS is now rising early enough in morning twilight to be seen even with small telescopes under imperfect conditions. Here's an image from this morning through thin clouds using a 152-mm Ritchey–Chrétien reflector.
Nov 2 at 3:13amWeb
Show threadKevin FreitasNov 2
@qicheng Amazing! Was hoping to try to capture it here in #Seattle but have rain in the foreseeable forecast. May try to dodge clouds…
Show threadDaniel FischerNov 2
@qicheng Cool! Can you 'generate' a V (or vis.) magnitude from this observation?
Show threadQicheng ZhangNov 2
@cosmos4u Not easily, as it looks like most of the brightness is in the diffuse outer coma, which is still largely hidden by the sky. In photometry, I can detect faint signal in the g' stack out to ~1' from the nucleus (i.e., ~2' diameter), within which I get g' ~ 10.3 (V ~ 10.1 at solar color, which is not quite right but maybe close). However, CCOR-1 images showed a coma twice this diameter, with a ~0.4 mag difference between the two apertures. That yields an extremely rough V ~ 9.7, from this pile of assumptions. Could be a few 0.1 mag brighter, since g' is actually more sensitive to the gas than CCOR-1, and the gas is more diffuse than the dust (leading to a bigger difference between the apertures).
Show threadDaniel FischerNov 2
@qicheng Thanks a lot! Next question would be the 'n' to use for extrapolating the remainder of the month ...
Show threadQicheng ZhangNov 2
@cosmos4u Yeah, that's a tricky question since it depends on the reason for the fast brightening. If it was just because of the fast speed + time for the CO2 ice to "burn" off from the surface, I could see it fading with a more typical n ~ 4 (possibly with a delay), since the surface CO2 won't be coming back. If it's because it's like the short-period comets that brighten as quickly (which I'd find surprising given the distant activity), it could fade as quickly as it brightened. Or it could be another reason that might imply either or some other rate.
Show threadJorma RyskeNov 3
@qicheng Great, 3I is back. Here my observation of this interstellar #comet 3I/ATLAS taken today 3.11.2025 light morning sky with 0.3m telescope (Y71) from Spain. Red filter image measured magnitude around 10.7, Green filter image shows diffuse coma. 3I was only 10 degrees above horizon and Sun 7 deg below.