About the Subject

M101, also known as the "Pinwheel Galaxy,” is a large spiral located in the constellation Ursa Major. It is roughly twenty-one million light years from Earth making it one of the closest large spirals. It is almost twice as large as our Milky Way, with a diameter of roughly 170,000 light years. Along with M51, the Whirlpool Galaxy, M101 was one of the first galaxies visually observed to have a spiral structure. That structure was first detected by Lord Rosse using a 72 inch diameter Newtonian reflector. M101 is estimated to have roughly one trillion stars, similar to the Andromeda Galaxy. It has a relatively low density, though, compared to the Milky Way. It is estimated to have a stellar mass of roughly fifty-three billion times the Sun, only slightly higher than the Milky Way itself. M101 is undergoing a large amount of star formation which can be seen in the red/magenta H II regions scattered throughout the spiral arms. Each of these areas represents a dense cloud of hydrogen gas that has been ionized and lit up by the new, bright stars forming from the collapsing clouds of gas. The irregular shape of M101 resulted from tidal forces during recent interactions with companion galaxies including NGC 5474 and NGC 5477. It's these same tidal forces that are triggering the waves of star formation.

About the Image

The data for this image were captured between May 11 and May 22, 2026 from Deep Sky West observatory in Rowe, NM. NINA was used for image capture, APCC was used to control the mount, and PixInsight was used for image pre-processing and post.

Location, and Equipment:

• Rowe, NM, USA

• Astro-Physics 305mm Riccardi-Honders Cassegrain @ f/3.8

• Astro-Physics 1100GTO AE Mount with Absolute Encoders

• QHY600PH Monochrome Camera at -10°C

• Chroma 50mm x 50mm filters

  • 3nm H-Alpha

  • 3nm OIII

  • RGB

• Total integration time of 31h 16m (7h 30m red, 7h 24m green, 7h 12m blue, 6h 55m Ha, 2h 15m OIII)

Software:

• Astro-Physics APCC for mount control and advanced pointing model

• NINA for autofocus, sequence of images, and camera control

• PHD2 for guiding

• PixInsight for calibration and all post processing