Comet C/2023 P1 (Nishimura) was only discovered two weeks ago on August 12 by Hideo Nishimura, but STEREO-A actually saw the comet a month earlier through its HI1 camera. Here's a combined stacked frame and a short animation of the comet brightening in July.
Here's my experimental spot on the Fediverse. I ponder comets, asteroids, and various extrapolations of such things. Currently a planetary science Ph.D. student at Caltech.
Here's a peek at the approaching Oort cloud comet C/2023 A3 (Tsuchinshan-ATLAS) by the 200-inch Hale Telescope at Palomar Observatory last month. Coma was at an r' magnitude of ~16.3.
Planet Mercury reaches inferior conjunction today. While not a "proper" transit as it misses the photosphere by almost half a degree, Mercury's lack of a substantial atmosphere (unlike Venus) makes it extremely dark at high phase angles, which enables SOHO's LASCO C2 coronagraph to see the disk of the planet (~1 px diameter) silhouetted as a black dot against the bright solar corona.
Asteroid (3200) Phaethon has been known to brighten and grow a tail like a comet while near the Sun. This activity turns out to not be from comet-like dust as previously assumed, but rather the bright orange glow of sodium atoms escaping from the asteroid's surface under intense solar heating. Our results combining data from SOHO's LASCO coronagraphs and STEREO's HI1 imagers are published here: https://iopscience.iop.org/article/10.3847/PSJ/acc866
Newly confirmed comet C/2023 A3 (Tsuchinshan-ATLAS) = A10SVYR will pass only 3 degrees from the Sun as seen from Earth on 2024 October 9-10 at an extremely high phase angle of 173 degrees. If the comet is large/bright enough to survive its 0.39 au perihelion passage, the extreme forward scattering will likely boost the dust to at least 0th magnitude to be brightly seen by at least SOHO's LASCO C3 coronagraph (along with STEREO-A's HI1, and maybe the future GOES-U/19's CCOR-1) and quite possibly even in broad daylight from the ground if it turns out to be a bit brighter. C/2010 X1 (Elenin) was the last (non-SOHO/STEREO-found) long-period comet to reach such high phase angles, but it actually disintegrated first and left nothing to be seen there, an alternate fate that also remains quite possible for C/2023 A3 with the limited information available so far.
Interesting new comet candidate A10SVYR on the PCCP to keep an eye on. Looks like it will pass almost directly between the Earth and Sun in 2024 October, where forward scattering could make the comet fairly bright in twilight if it survives to that point: https://catalina.lpl.arizona.edu/css-orbit-view?Namev=A10SVYR&JDTv=2460580&av=0&Mv=0&ev=1&Iv=139.16&Periv=308.4&Nodev=21.52&Pv=0&qv=0.392&Tv=2460580&Cx=499&Cy=402&Cz=769&CZ=143
Comet 96P/Machholz has emerged into the predawn sky following its perihelion passage earlier this week. Here it was this morning from Pasadena, at ~2 degrees above the horizon and ~14 degrees from the Sun, with a hint of the first ~5' of its dust tail. Very rough photometry gives a coma r' magnitude of ~7. Observing conditions will rapidly improve over the next week as the comet fades.
Here's comet C/2022 E3 (ZTF) from last week, which looks fairly similar to (albeit brighter than) the view through the eyepiece under light polluted Pasadena skies last night. It's actually not that green of a comet, with its coma brightness being overwhelmingly from dust rather than gas.
Comet 96P/Machholz has just reached its perihelion, at only 0.12 au from the Sun. Here's the view from the SOHO spacecraft's LASCO C3 coronagraph, which has been running a special program observing the comet through several color filters over the last couple days.