October 2019 - Picture of the Month
Messier 33 in Triangulum
It's been a while so I've gone for a galaxy this month. I've tried observing this fascinating galaxy visually on many occasions, and the best view has been with large binoculars. As David points out below, in bright skies this is a tricky galaxy to observe and, it seems, to image as well.
I first imaged M33 in October 2011 with a 120ED refractor and a DSLR. I realised then that M33 is a difficult target to do justice to: whilst the principle spiral arms are quite bright, the outer regions of the galaxy have very low surface brightness and are difficult to capture.
M33 is the third largest galaxy in our Local Group after M31 and the Milky Way. It is smaller than M31 at 50,000 to 60,000 light-years across and is around 2.75 million light-years away.
It is almost face-on to us, so although the integrated brightness is magnitude 5.7, the surface brightness is around magnitude 23/arcsec squared. It, therefore, makes an extremely challenging naked eye target and can be glimpsed only in the darkest of skies.
M33 appears blue in colour due to the many star-forming regions with many young stars mingled with numerous pink HII regions. Northeast of the centre of the galaxy is a massive HII region designed NGC 604. This is one of the largest HII regions known and would reach from the Earth to the Orion Nebula if it was located in the Milky Way.
The image comprises 100 minutes each of red, green and blue in five-minutes subs plus 120 minutes of luminance, also in five-minute subs. Gathered with a 107mm APM triplet and an QSI 583 camera.
James Whinfrey - Website Administrator.