Spiral Galaxy
NGC 598
1H 33.9m +30° 39'

Magnitude: 5.7
Size: 73' × 54'
Distance: 3 million light-years


Suitable for beginners

Skill Level
M33 is a great target for beginners. You can capture a recognizable image with 15-second subs. With increasing exposure length, M33 reveals more detail and color.

NovemberBest Month
M33 is visible in Autumn in the Northern Hemisphere. November sees M33 high in the sky at midnight.

Recommended Equipment
Size and brightness make M33 an ideal target for a small refractor. At a 400mm focal length you should be able to fit the entire galaxy in a single frame of the DSI.

M33 is too big for a medium-sized Newtonian (like the SN8) and a DSI. Try for a mosaic (like the image above) or use a DSLR to get a wider field of view.

Long focal length SCTs are not well-suited for M33. Use a focal reducer and a wide-field camera, or concentrate on details of the galaxy (such as NGC 604).


Image Stats
Meade 8" SN LXD75
Meade DSI Pro II
Meade RGB + IR filters

2 × 2 RGB mosaic
(Approximately 30 minutes per channel)

Good to excellent transparency
22, 28, 29 November 2008
San Mateo, CA

One thing I've always loved about the Impressionists is how a painting of a beautiful and colorful landscape turns into a random splatter of colors when you get close. Galaxies are the same way. From a distance you can see their beautiful spiral patterns but up close they look like a chaotic splattering of stars.

Unlike paintings, however, we cannot easily switch our view of a galaxy from close to far and vice versa. Most galaxies are so far away that we see only the grand pattern (at least with amateur instruments). The Milky Way is so close that all we see are the stars—the pattern is lost to us. Fortunately, M33 is right in between. Far enough that we can trace its ragged spiral arms, but close enough that we can begin to see the random splatters that compose them.

M33, "only" three million light-years away, is the second closest spiral galaxy to Earth, after the Andromeda Galaxy. At that close distance M33 appears larger in the sky than two full moons side-by-side. We can easily take pictures of M33 that resolve its stars and reveal its bright nebulae and clusters.

Nebulae in M33

Objects in M33

Dozens of nebulae and star clusters have been identified and named in M33. Most are clouds of ionized hydrogen (known as H II regions) lit up by newly born stars. The chart above shows some of the more prominent regions.

NGC 604

NGC 604NGC 604 is the largest H II region in M33 and one of the largest know. It is nearly 1,500 light-years across, far larger than the famous Orion Nebula (12 light-years across). Though only one arcseconds in diameter its bright pink and purple hues stand out amid the blue disk.

A good advanced project might be to take a high-magnification photo of NGC 604. It is no smaller than a small planetary nebula, and it might be possible to tame its dynamic range by exposing its edges longer than its core.

Imaging Notes

M33 is a bright galaxy so you won't have to stretch the dim zone much. Concentrate instead on getting good contrast and sharpness. The lanes of dust, set against the bright disk, help to define the otherwise ragged arms. M33 is also large enough that you can resolve some of the stars in its disk. Make sure your noise reduction process is not too aggressive—the arms should look mottled and grainy, like a minature version of the Milky Way.

It's not too hard to get good color in M33. Try to maximize the contrast between the reddish-purple nebulae (like NGC 604) and the light blue of the disk. The dust clouds are a neutral, light brown and the core is white. It's tempting to increase the brightness of the red channel to get the nebulae to show more clearly, but if the core of the galaxy starts to look pink, then you've increased it too much.