I’ve now added another 20 minutes of luminance frames and 12 minutes each of red, green and blue to this data set and stacked with the original 20 minutes of luminance to create a colour image.
Just to the right of M83, 2 background galaxies are just visible. These are PGC724525 (closest to M83) and PGC48132 and are about magnitude 16.
M101 is another spiral galaxy in Ursa Major but because it is presented face on it is rather faint and difficult to see in binoculars unless you have a very dark sky. Overall, the spiral arms cover an area almost the size of a full moon. However, in small telescopes only the central core will be visible.
27 million light years away, it’s discovery is credited to Pierre Méchain in 1871 and it’s spiral structure was first described by Lord Rosse in the 19th century using his 72″ reflector. It’s diameter of 170,000 light years is about twice the size of our own Milky Way galaxy. An unusual feature of this galaxy is the large number of star forming areas in the spiral arms. Some of these can be seen in this image as small bright regions with the characteristic blue tint of hot young stars.
Ongoing problems with tracking limited the maximum sub-exposure times to 120 seconds and a lot of these still had trailed stars leaving me with a stack of 16. As a result, the final image is rather noisy.
Friday evening was clear with some haze low in the sky, but, with Ursa Major high in the sky, presented an opportunity to try imaging M81 again. The CG-5 mount had some problems with intermittent tracking resulting in a lot of trailed images which had to be discarded and the corrector plate of the Celestron was fogging on the inside due to the high humidity. None of the images obtained were of good quality and I suspect the secondary mirror had fogged as well.
Despite the problems, 19 2 minute images were stacked and processed for this image:
Much more detail is apparent than in my earlier attempt. The Celestron is now drying out in a room with a de-humidifier running so hopefully the fogging problems won’t be repeated next time out.
The first galaxy to be discovered, outside of the local group, M83 was first catalogued as Lac.I.6 by Nicholas Louis de la Caille from his Cape of Good Hope observatory in 1752. It was re-catalogued by Charles Messier in 1781 who, observing from Paris, noted “it appears as a faint & even glow, but it is difficult to see in the telescope, as the least light to illuminate the micrometer wires makes it disappear. One is only able with the greatest concentration to see it at all”.
This monochrome image is a stack of 10 2 minute exposures using GRAS-15 in Australia processed in Maxim DL. Despite the near full moon this image clearly shows the dust lanes that wind their way down the spiral arms to the compact nucleus.
