What Is The M33 Triangulum Galaxy?
The M33 Triangulum Galaxy (M33, Messier 33 or NGC 598) is a beautiful spiral galaxy in the small triangle-shaped constellation Triangulum, 2.73 million light-years away from Earth. This galaxy is the third-largest member of the Local Group of galaxies, behind the Andromeda Galaxy and the Milky Way, and is believed to be a satellite of the Andromeda Galaxy. It is one of the most distant permanent objects that can be seen with the naked eye under very good seeing conditions with no light pollution and good eyesight.
M33 was probably discovered before 1654 by the Italian astronomer Giovanni Battista Hodierna. The Triangulum Galaxy was independently discovered in 1764 by Charles Messier and was published as object number 33 in his Catalogue of Nebulae and Star Clusters.
Astrophotography
Visually, M33 is difficult to spot, but with long exposure photography, you can reveal the most fainted details of the Triangulum Galaxy.
For the image above, I’ve used different exposures: 60sec; 90sec; 120sec, and 300sec. 60 seconds to keep the core sharp and not overexpose it. 300 seconds to reveal more of the spiral arms. Unfortunately, I had to throw away a lot of 300-sec subframes because of the “not-so-good seeing” that night. Otherwise, the spiral arms would be more visible. The 90-sec and 120-sec subframes were just test shots that were OK and therefore I stacked them together with the 60-sec and 300-sec exposure time subframes. The camera I used was the ZWO ASI294MC Pro attached to my 8″ Newtonian, a Sky-Watcher Telescope Explorer Black Diamond N200/1000.
On the two first imaging nights, I used the ZWO UV/IR cut-off filter 1.25″ and on the third imaging night I used the Optolong L-Pro filter 2″.
Why 2 different filters?
I wanted to test out for myself the differences between these filters. Because the ZWO ASI294MC Pro has only an AR coating (anti-reflection coating) on the sensor, it’s recommended to use a UV/IR cut-off filter to prevent the stars from blowing out, especially with longer exposure times. Another advantage of the UV/IR cut-off filter: it shows your object of interest still in a more natural way compared to other, more aggressive, filters that can mess up the color balance of your image.
The Optolong L-Pro filter, on the other hand, is a multi-purpose filter but it is also an excellent choice for broadband galaxies like M33. The L-Pro filter suppresses light pollution and allows astrophotos to be taken with the minimal color cast to broadband emission objects. In other words: this filter gives a beautiful, dark background and boosts up the object in your image. It enhances the contrast. With the Optolong L-Pro, the hydrogen gas (pink areas in the spiral arms) becomes more visible than with a UV/IR cut filter, because the L-Pro filter lets more of the H-alpha wavelength through.
Image details
- Telescope: Sky-Watcher Explorer Black Diamond N200/1000
- Mount: iOptron CEM60 on iOptron tri-pier
- Camera: ZWO ASI294MC Pro
- Filter: 1) ZWO UV/IR Cut 1.25″ (ZWO EFW Mini) // Optolong L-Pro 2″
- Telescope control: ZWO ASIair v1
- Software: Astro Pixel Processor (stacking) & PixInsight (processing)
Data captured on the nights of 07/09-08/09/2021 (ZWO UV/IR) & 09/09/2021 (ZWO UV/IR) // 27/10-28/10/2021 (Optolong L-Pro)
Total integration time: 5.84 hours
SQM-L (average): 19.08 -> Bortle class 6
No guiding, no coma corrector
