APOD: 2023 January 17 – Unexpected Clouds Toward the Andromeda Galaxy

Good evening, Rallypoint, and welcome to the January 17th edition of Astronomy Picture of the Day (APOD): "Unexpected Clouds Toward the Andromeda Galaxy." So much for settled science. The blue arc shown in today's APOD was only discovered in August 2022. Amateurs first noticed the unexpected presence of oxygen by using an OIII (oh 3) filter when imaging what they thought was the well-understood Andromeda Galaxy (M31).

Their findings were quickly confirmed across the globe. New questions arose: is it a segment of a galactic supernova remnant? A bright part of an ancient planetary nebula? If the arc is in close proximity to M31, is it due to galactic mergers with M31? Or maybe (if the oxygen cloud is closer to us) is it an interaction shock wave between the Milky Way and M31? I'll post a video about this discovery in a separate comment. If you've got the time, its worth the extra 7+ minutes.