When I started this project I had no specific aspect I was focusing on and no big expectations towards the result. I had imaged M33 before - as probably most astrophotographers at some point. Back in 2020 from my backyard with bad seeing and worse light pollution (and no Broadband data) it turned out rather underwhelming.

With 50+ hours of total integration, good seeing, low light pollution and the addition of Ha and O3 data this has turned into a great journey to one of our close neighbours - with spectacular nebulas and structures. I will mainly cite from a wonderful description from www.deepskycorner.ch and do my best to translate, as the original is in German. I will not list the citations, as refered to on the website, as they are listed in detail there: 
This galaxy was first observed by the Italian astronomer Giovanni Battista Hodierna using a small refracting telescope in Palermo. At that time, he discovered a variety of nebulas, many of which are known today, but unfortunately, his publication in 1654 received little attention outside of Sicily. On August 25, 1764, the galaxy was observed by Charles Messier and entered as the 33rd object in his list. He wrote: "The nebula is of whitish light, of almost equal density, but slightly brighter at two-thirds of its diameter, and contains no stars. It is difficult to see it with an ordinary telescope of one foot."Wilhelm Herschel observed the nebula on September 11, 1784. He classified it as V 17 and described it as a "milky nebula, no less than 1/2 degree wide, perhaps 3/4 degree long, but not determined." He also noticed a small, faint nebula nearby, which he cataloged as III 150 and later became known as NGC 604.In 1850, Bindon Stoney used the enormous 6-foot aperture telescope "Leviathan" of his employer William Parsons, 3rd Earl of Rosse, and discovered a large spiral structure full of knots. [485, 486] The brightest three of the knots were later numbered by Dreyer as NGC 592, NGC 595, and NGC 603. In 1889, the French astronomer Guillaume Bigourdan found additional knots with a 12.4-inch refractor, which received IC designations.
From: https://www.deepskycorner.ch/obj/m33.de.php on 31.12.2023


As mentioned, even Wilhelm Herschel was able to pick up NGC 604 back in the 18th century. While I couldn't find a source with information on which telescope he used for this observation, it definitely was not the 40 inch completed in 1789, but more likely a much smaller refactor, like the 6,2 inch he used from his backyard. Despite these optics and definitely no help of cameras or stacking he was able to see this this structure - and it truly is mind blowing: it spans nearly 1500 light years and is about 100 times larger than the Orion nebula and contains more than 200 hot, massive, young stars (versus the Orion Nebula’s four) [[url]https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-33/]



Crop1: NGC604 in resolution 0.67 "/ Pixel. FOV= 12,9'x8,5'
The best photographs show M33 with an angular size of about 67'x41.5'. The visual diameter is usually around half a degree. The integrated photographic brightness is 7.8 mag, and the visual brightness is 5.7 mag. However, the surface brightness of M33 is very low, measuring only 14.2 mag. [...]Regarding the distance of M33, literature provides values ranging from 2.4 to 3.6 million light-years. It is likely close to 2.5 million light-years. M33 is moving towards us at a speed of about 200 km/s while simultaneously moving away from the center of the Local Group at 68 km/s. It is the closest spiral galaxy after the larger and less irregular Andromeda Galaxy, M31, and one of the most distant members of the Local Group. Galaxies M31 and M33 are only about 570,000 light-years apart. After the Andromeda Galaxy and the Milky Way, M33 is the third-largest member of the Local Group.
From: https://www.deepskycorner.ch/obj/m33.de.php on 31.12.2023

With the large telescopes of professional observatories, it is easy to resolve this galaxy into individual stars. It exhibits a massive two-armed spiral structure of star clouds revolving around the bright core region. The arms are thick and clumpy, dotted with nebulous regions, and the spiral structure is loose and irregular when compared to more symmetrical galaxies like M81. [...]
Including the finest extensions of the spiral arms, the galaxy measures about 60,000 light-years along its major axis. According to a study by E. Holmberg, the mass of visible stars in M33 is approximately 8 billion solar masses, and the total light is about 3 billion times brighter than the Sun, or about -19 mag absolute. The galaxy rotates clockwise, dragging its arms like a fiery wheel. The orbital period in the outer region has been calculated to be 200 million years.
From: https://www.deepskycorner.ch/obj/m33.de.php on 31.12.2023

In the 1920s, astronomer Edwin Hubble studied dozens of variable stars (those that periodically change brightness) in M33, which helped him to estimate the object’s distance and prove that M33 is not a nebula within our own galaxy, as previously suspected, but actually a separate galaxy outside our own.
From:https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-33/ on 31.12.2023


Further highlights also included in the NGC and IC catalogue:

IC 132 is understood to be a planetary nebula, much similar to the Dumbbell Nebula M27 in our own Galaxy. The strong O3 Signal in this nebula would be typical for such an object.
The Nebula IC133 shows a strong signal in Ha and O3. This could resemble a similar object as the Vail Nebula in our own Galaxy.

Crop2: IC132 and IC1333 in resolution 0.67 "/ Pixel. FOV= 13,0'x8,5'



IC131 look s a lot like the Orion Nebula of M33 to me. Again strong Ha and O3 Emissions are present. There is a very strong X-Ray Source present in the south-eastern part of the Nebula [Ralph Tüllmann [i]et al 2009 ApJ707 1361DOI 10.1088/0004-637X/707/2/1361]


Crop3: IC131 in resolution 0.67 "/ Pixel. FOV= 13,0'x8,6'



Many more exciting features and Objects from the NCG and IC catalogues could be mentioned. 

I invite you to journey through the image.

Enjoy
Robert