About the Object
M101, also known as the "pinwheel" galaxy,  is a very 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. 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 magenta areas represents a dense cloud of hydrogen gas has been  ionized and lit up by the new, bright stars forming from the collapsing clouds of gas. The irregular shape of M101 was created from tidal forces during recent interactions with companion galaxies including NGC 5474, NGC 5477, both of which are visible in this image.  It's these same tidal forces that are triggering the waves of star formation. 

This image also shows supernova SN2023ixf located near NGC 5461 in one of M101's spiral arms. This supernova was first detected on May 19th, 2023 by an amateur astronomer in Japan named Koichi Itagaki. From looking at its spectrum, it was classified as a Type II core collapse supernova. The suspected progenitor star likely had a mass roughly fifteen times greater than the Sun. The peak brightness for this supernova was 10.8 meaning that at its brightest, the supernova was about 1/15th as bright as the entire Pinwheel galaxy--roughly 1.5 billion times brighter than the Sun.

About the Image
This image was taken with a 305mm Riccardi-Honders telescope running at f/3.8. The Riccardi-Honders design is a little unusual in that it uses a Mangin primary mirror where the reflective surface is on the back side of the mirror, not the front, allowing the glass of the mirror to act as a lens not just as a substrate to hold the reflective surface. All surfaces in a Riccardi-Honders are spherical and are made out of ordinary optical crown glass, reducing cost and complexity in manufacture. However, the mechanical tolerances for a Riccardi-Honders to produce good results are extremely tight, making careful design, manufacturing and assembly critical. F/3.8 is considered quite fast for a well corrected telescope, resulting in a moderate focal length and a wide field of view. There are several down sides to the Riccardi-Honders design. First, because the optics are made entirely of crown glass they are not stable with changing temperatures, so frequent re-focusing throughout the night is required. Second, the f/3.8 design requires an extremely large secondary mirror making the telescope suitable only for astrophotography; it can not be used effectively as a visual telescope.

The mount used is an AP1100GTO AE which includes high precision encoders. These encoders, coupled with a very precise pointing model, allows the telescope to track accurately without the need for an auto guider. The pointing model incorporates correction factors for atmospheric temperature and pressure, misalignment of polar axis, variations in tracking speed due to imperfections in the gears, sagging of the telescope and mount under gravity in various physical positions, etc. 

The camera used is a QHY600 which incorporates a 36mm x 24mm Sony sensor (full frame). The sensor has extremely high quantum efficiency at most visual wavelengths as well as very low read noise, making it well suited to astrophotography whether in a dedicated astronomy camera or a mirrorless terrestrial camera such as the Sony A7RIV. Because of the fast focal ratio of the telescope, the light cone going into the camera is extremely steep, resulting in the need for large RGB filters to fully cover the edges of the frame. In this case, the filters are 50mm square Chroma branded red, green, and blue filters. 

A total of just over six hours of integration time were incorporated into this image which is well below my typical exposure time for an object like this, but this is what weather, short summer nights, and the lunar cycle allowed. Please note that the annotated version of the image includes a marked location for the supernova with a label in dark green. In addition, other prominent catalog objects within the field of view as well as roughly 900 faint background galaxies are shown.