M33, often called the Triangulum Galaxy since it is in that constellation, is the other rather large galaxy in our local group along with M31. Like M31 it is also approaching us but won't arrive here until well after we've merged with M31. Though eventually, all three will become one along with a lot of dwarf members of the local group that weren't ejected by these big boys gravity. Distance estimates range from 2.8 to 3 million light-years. Since it doesn't fit my field of view I have to use published size measurements of 70.8' at NED to estimate its size. That would make it about 58,000 to 62,000 light-years in size or about half that of M31. NED classifies it as SA(s)cd HII while Seligman adds a question mark SA(s)cd?. It contains one of the largest HII regions known. Originally it had enough mass to create a globular cluster though only created a rich open cluster. the detailed HST image is at: https://apod.nasa.gov/apod/image/1212/ngc604_hstlegacy_1512.jpg

Seen more face on than M31 its HII regions are much easier to see. Also, it seems to have far more big ones than M31. Many have IC and NGC numbers. I've included an annotated image showing all the IC and NGC nebulae and star clusters. Obviously, there are far more. They have names that only are positional which are long and would make a mess of the image so I didn't bother with them.

M33 was likely first recorded by Giovanni Hodierna before 1764. Though it is barely visible naked eye from a good site. I need averted vision to see it. Being visible naked eye I suppose someone saw it thousands of years ago and wondered what that fuzzy thing was but never recorded it. Even Hodierna's observation went unknown for 300 years. Thus it was Charlies Messier who brought it to the attention of astronomers when he added it to his list on August 18, 1775. William Herschel recorded it on September 11, 1784. Even though already in the M object observing program the AL put it in their original Herschel 400 program as well. My log from that on July 14-1985 with my 10" f/5 at 60x on a night with bright auroral activity visible from here in northern Minnesota reads: "Large, face on spiral. Two arms easily seen as is NGC 604. It is surprisingly good considering the auroral activity I'm having to observe through."

NGC 604 has been mistaken for a comet by more than one amateur on this list that shall remain nameless. It was discovered by William Herschel on September 11, 1784. It is in the second Herschel 400 program. Unfortunately, my notes from that didn't survive the move up here.

NGC 595 is another emission nebula. It was discovered on October 1, 1864 by Heinrich d'Arrest.

NGC 592 is a star cluster in an emission nebula. It was discovered by d'Arrest several 3 years before he saw NGC 595 on October 2, 1861.

NGC 588 is an emission nebula with a small star cluster in it. It was also found by d'Arrest on October 2, 1861.

IC 131 is often mistaken for the bright star with emission around it that is just west of the real IC 131 which is an emission nebula and star cloud per the IC description. Also the position better matches the object I've identified as IC 131. It was first seen by Guillaume Bigourdan on October 28, 1889.

IC 135 is on the eastern side of the galaxy showing many of the IC objects in this galaxy fail to follow RA order for some reason. It is an emission nebula and was discovered by Guillaume Bigourdan the same night as IC 131 and others. There's some uncertainty about the identification of this one. This is what most say is IC 135 but no one can fully make it work with Bigourdan's notes.

IC 136 is listed as an open cluster but it also is an emission nebula. At least the object I've identified as IC 136 is. It too is one Bigourdan found that fateful October night and it too doesn't quite fit his notes but again is the best anyone has come up with for this object.

IC 137 is an open cluster toward the south end of the galaxy. It too was found by Bigourdan that same night and it too has identification issues. Bigourdan's position is over a minute south of the object I've identified as IC 137 but it does match his description and there's nothing like it at his position so another somewhat questionable ID.

IC 139 is listed as an open cluster but I see emission nebula in it. Another Bigourdan discovery that October night. But this one has a rather certain identification for a change.

IC 140 northeast of IC 139 is an open cluster. Yep, another Bigourdan discovery that same night. Like 139 identification of this one seems certain.

IC 142 is listed as a star cluster though emission nebula surrounds it in my image. It is well north of the galaxy's core. Another Bigourdan discovery that October night. One that also has a rather certain identification

IC 143 lies northeast of IC 142 and is an emission nebula. Another Bigourdan find that October night. Its ID is pretty solid.

Many other nebulae, star clouds and star clusters can be seen in my image. I only identified those in the IC and NGC catalogs.

For a lot more on M33 see: http://messier.seds.org/m/m033.html

14" LX200R @ f/10, L=4x10'+3x30Ha, R=2x10'+80% HA, G=2x10' B=2x10+20%Ha, STL-11000XM, Paramount ME