Daniel FischerThe #GeminiNorth telescopes is observing the interstellar comet #3IATLAS right now: here is the acquisition image from moments ago, spectra to be taken now - from the #ShadowTheScientists session.
And here is now also a spectrum of #comet #3I/ATLAS taken during the #ShadowTheScientists session on 26 November, from https://www.astronomerstelegram.org/?read=17561 - CN (388 nm), C3 (402 nm) and C2 (474 nm/517 nm) are detected. Meanwhile the paper https://arxiv.org/abs/2512.18341 concludes from the non-gravitational acceleration that the diameter of the comet's nucleus is 820 to1050 m.
Finally an RGB image of comet #3IATLAS from images taken by #GeminiNorth during the 26 November #shadowTheScientists session: https://noirlab.edu/public/news/noirlab2532/ - the coma has become bluer due to more gas emission. Also published today: an X-ray image by XMM-Newton at https://www.esa.int/ESA_Multimedia/Images/2025/12/XMM-Newton_sees_comet_3I_ATLAS_in_X-ray_light with explanations in http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET005646.txt which also contains more 3I news.
Meanwhile the paper https://iopscience.iop.org/article/10.3847/2515-5172/ae2915 claims an upper limit for 3I's nucleus diameter of only some 750 meters from the measured non-gravitational acceleration (NGA) parameters: that would be waaay more stringent than the 5.6 km upper limit from early Hubble observations reported in https://iopscience.iop.org/article/10.3847/2041-8213/adf8d8 (where also a lower limit of 440 meters is stated).
And here is a recording of the #ShadowTheScientists live observation of interstellar comet #3IATLAS with #GeminiNorth a few hours ago: https://www.youtube.com/watch?v=cW0chiPZyYM
Nov 26, 2025: Exploring Comet 3I/ATLAS - A Rare Encounter with an Interstellar Visitor
And here is what comet #3IATLAS looks like for the #geminiNorth Integral Field Unit (IFU) taking numerous spectra from points across the coma - from #ShadowTheScientists
What a #GeminiNorth #3IATLAS spectrum looks like - as raw as it gets, from the #shadowTheScientists session. See https://www.astronomerstelegram.org/?read=17503 for a pre-perihelion spectrum.
