After we say goodbye to Orion each year, the galaxy season starts in February and lasts through until late April. It seems almost unbelievable that the existence of galaxies outside of our own Milky Way was unknown to mankind until Edwin Hubble’s work in 1929; the Andromeda Nebula turned out to be a galaxy as did all those other faint fuzzies and many more that have since been discovered. Like grains of sand on the beach, there are currently known to be at least two trillion galaxies in the observable Universe and no doubt many more as yet remain undiscovered. On Earth we really are a very, very small speck in space and can only wonder at those other worlds.
Despite their abundance I struggle to image galaxies with the otherwise excellent William Optics GT81 telescope, except for the few largest ones that are closest to Earth in the so-called Local Group, such as the aforesaid Andromeda Galaxy and located nearby M33 or the Triangulum Galaxy. About one quarter the size pf Andromeda, M33 still provides a decent imaging target for my equipment, which I’ve attempted before using a DSLR camera with some success. So, before the winter night sky arrives I thought I’d give M33 a try for the first time using the ZWO1600MM-Cool CMOS mono camera.
M33 is characterized by its large, sprawling spiral arms, within which are located numerous H-II regions, home to large stellar nurseries. Its mass is thought to extend well beyond the visible galaxy, with large areas of cold dust now identified around and beyond the spiral arms. Interestingly infrared imaging by the Spitzer Space Telescope (below) shows much more discrete structures throughout the disc than is evident in the visible light spectrum. The future of M33 is somewhat uncertain but seems to point towards its destruction, either by Andromeda or alternatively crashing into the Milky Way!
Imaging experience to-date with the ZWO camera has shown that 5-minute exposures and unitary settings – Gain 139 Offset 21 – produces a good result with most nebulae targets, however, imaging star clusters and galaxies remains work-in-progress. Whilst tempted to continue with this approach, after reviewing and adjusting the PHD2 settings my guiding has been poor recently, so on this occasion I chose shorter 3-minute exposures to obtain LRGB and Ha subs.
With nearly 3-hours integration time the resulting LRGB image turned out good (top-of-the page) and noticeably better than using a DSLR camera. The H-II regions were captured with the Ha-subs but subsequently did not integrate very well with the main LRGB image – or maybe that was my error? Whilst pleased with the outcome for now, on reflection I think there are issues that still need to be addressed in order to obtain a better outcome next time:
- Although M33 is quite bright, the spiral arms are somewhat diffuse in nature and would benefit from much longer integration time and better guiding to achieve less noise and greater depth in the resulting image;
- The jury’s out on exposure times but I feel that 5-minutes might still work better and is certainly worth trying;
- Though much improved, processing remains a weakness and needs to be improved.
Notwithstanding the above M33 is a wonderful object and, as ever, I remain inspired by the galaxy itself and images of others to do better in the future.
| IMAGING DETAILS | |
| Object | M33 Triangulum Galaxy |
| Constellation | Triangulum |
| Distance | Approx.. 2.7 million light-years |
| Size | 71’ x 42’ or 60,000 light-years |
| Apparent Magnitude | +5.72 |
| Scope | William Optics GT81 + Focal Reducer FL 382mm f4.72 |
| Mount | SW AZ-EQ6 GT + EQASCOM computer control |
| Guiding | William Optics 50mm guide scope |
| + Starlight Xpress Lodestar X2 guide camera & PHD2 control | |
| Camera | ZWO1600MM-Cool (mono) CMOS sensor |
| FOV 2.65o x 2.0o Resolution 2.05”/pix Max. image size 4,656 x 3,520 pix | |
| EFW | ZWOx8 + ZWO LRGB & Ha OIII SII 7nm filters |
| Capture & Processing | Astro Photography Tool + PS2, Deep Sky Stacker & Photoshop CS2, HLVG |
| Image Location & Orientation | Centre RA 01:34:02 DEC 30:38:51
Top = North Right = West Bottom = South Left = East |
| Exposures | 12 x 180 sec RGB + 10×10 sec L & Ha (Total time: 168 minutes) |
| @ 139 Gain 21 Offset @ -20oC | |
| Calibration | 10 x 180 sec Darks 20 x 1/4000 sec Bias 10 x Flats LRGB + Ha @ ADU 25,000 |
| Location & Darkness | Fairvale Observatory – Redhill – Surrey – UK Typically Bortle 5 |
| Date & Time | 9th October 2018 @ +22.00h |
| Weather | Approx. 12oC RH = 90% |
The Heart and nearby Soul Nebula are situated in a busy region of the sky (see above – from Wikisky), which also contains seven open clusters of young stars, as well as the Pacman Nebula and galaxies of Maffei 1 & 2 and M31 Andromeda. The discovery of a bright fish-shaped HII object – known as the Fishhead Nebula IC 1795 or NGC 896 at the edge of the main object – preceded that of the Heart Nebula itself in 1787 by William Herschel. The Heart Nebula has a red glow, a result of intense radiation emanating from a small cluster of large, hot, young (1.5 My) bright-blue stars at the centre known as Melotte-15. The stellar wind and stream of charged particles that flow out from these newborn stars then creates the characteristic heart-shape of the nebula from the stellar dust and hydrogen gas clouds.
The aforesaid object of interest was the Elephant’s Trunk Nebula or IC 1396, a very large emission nebula, which in narrowband shows wonderful colour and detail (HaSHO above). IC 1396 consists of glowing gas illuminated by an open star cluster, broken up by intervening lanes of dark interstellar dust clouds. The ‘trunk’ itself, designated IC 1396A, is the long dark area protruding from the lower edge of the image, spectacularly illuminated from behind by a bright star forming region; the image has been rotated 180o from its natural position. Top right on the edge is the red supergiant Mu Cephei or Herschel’s Garnet Star, one of the largest and brightest known stars in the Milky Way, which in the position of the Sun would extend out to Saturn’s orbit!
When the object is right, such as the Rosette Nebula, narrowband imaging using the ZWO camera produces exceptional results. This is evident in these recent images where it’s now possible to clearly see structural elements of the nebula, as well as the star fields located within. Frankly I am very excited by these new images and can’t wait for next year to come around again!
