Andrew's Astronomy Blog

The constellation Draco is well placed, high in the sky at this time of year and contains some little known objects including this group of galaxies, NGC 5985, NGC 5982 & NGC 5981 (from left to right in the image).

NGC 5985 is classified as a barred spiral, 5982 an elliptical and 5981 is an edge on barred spiral. All three are about 100 million light years away and the field of view in this image is 23.6 arc minutes square.

I’ve had these images on my PC since the beginning of April while I tried to resolve an issue with calibrating them. Thanks to Arnie at GRAS, this is now solved and was due to a buggy camera driver not subtracting the camera pedestal value from each pixel.

Telescope is GRAS-1 with an FLI 1024 DM camera and this image is composed of eight 3 minute exposures.

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 9.25″ 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.

If the previous images of merging galaxies looked rather gentle then this is anything but. Several hundred million years ago, these galaxies were both spirals, rather similar to our own. Now, as the first image shows, they are almost totally disrupted with clumps of new stars ignited by the gravitational interaction.

The second image has been processed to over-expose the galactic cores and show the features that give this pair of galaxies their common name. Two gravity waves have produced long streams of stars, dust and gas stripped from the merging galaxies.

For astonomers wanting to study galactic interaction this pair present an ideal target as they’re are close neighbours at 45 million light years distance.

These images were produced on GRAS-15 and are a combination of 10x 300 second luminance frames binned at 1×1 and 6 each of red, green and blue filtered images binned at 2×2.