M33, Pinwheel Galaxy in Triangulum
| Target | Type | R. A. | Dec. | Constellation | Magnitude | Size |
| M33 (NGC 598) | Spiral Galaxy | 01h 33m 51s | +30° 39′ 36″ | Triangulum | +5.79 | 62×37 arcmins |
Overview
Fabulous images of this galaxy, like the one below, show it to be a sprawling spiral galaxy. It is just visible to the naked eye (under very dark skies), making it the most distant object visible to the naked eye, at 2.8 million light-years. It sits inside the constellation of Triangulum, on its boundary with Pisces and on the other side of Andromeda constellation from M31.
M33 was discovered by Giovanni Battista Hodierna prior to 1654. Charles Messier later discovered it again in August 1764.
From edge to edge, the arms of this galaxy span 61,000 light-years and is believed to orbit the most famous of all galaxies, M31, the Andromeda galaxy. It is the third largest member of the Local Group of galaxies after our own Milky Way and M31. Our galaxy may interact with M33 in as little as ten billion years as they are heading towards each other.
The galaxy has a low surface brightness. Although it is brighter than magnitude six, this light is spread over a large area, making it dim overall and susceptible to the negative effects of light pollution.
Finder Charts
The first sky chart, from SkySafari, shows the view at 8pm looking due east. See the galaxy we’re hunting is about midway between horizon and overhead (zenith). So that these charts can be used all year, they don’t show the moon and planets.
Triangulum is an constellation you’ve probably never considered much before and, fortunately, we don’t need it to signpost our way to M33. Instead, look for the instantly recognizable ‘W’ of Cassiopeia and use that to guide yourself into the legs of Andromeda.
Stars in the next chart are shown to magnitude 7.0.
We’ll use the distinctive Cassiopeia to point towards the stars Upsilon Persei and Almach (orange line). These are the bright stars at the end of Andromeda’s ‘legs’.
Next, trace up the almost parallel legs (yellow line) towards the stars Mu Andromedae and Mirach (Beta Andromedae). These two can then be used to signpost where in the sky we’ll find M33.
The third and final chart shows stars to magnitude 9.0. Use Alpha Trianguli (Metallah) to fine-tune the location. Our galaxy is just 4° from this star.
Now you’ve found the galaxy, what should you expect to see?
Individual Telescope Views
The following views will help you find M33 in different telescope types by presenting the images as your telescope will show them. The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Black stars on a white background is often easier to use at the telescope. Each image can be clicked on for a full-screen version. Stars are shown to magnitude 10.0.
Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope
Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal
Mirrored View – Refractors and Cassegrain models with a star diagonal show this view
Observation
This is technically visible to the naked eye, but don’t mistake that with being easy to see. As mentioned at the top of this page, M33 has a very low surface brightness and is easy to lose in the backdrop of light pollution.
That said, under good conditions, even a relatively small telescope can pull out the spiral shape of this distant island of stars. It’s a big view too, covering more than half of a 1° field of view, albeit with a very faint glow that is still easy to miss for all its size.
when you have it in view, you’ll see that low magnification does the best job of displaying contrast between the body of the galaxy and its background. The small, bright nucleus is home to just 2% of the galaxy’s total mass.
Larger telescopes will display the brighter spiral arms emerging from the slightly brighter heart of this galaxy. The galactic mass is home to star clouds and nebulae that have their own NGC or IC numbers. NGC 604 is a 12th magnitude nebula which is the brightest object in the galaxy after the nucleus.
PDFs for Printing
Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [M33-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.