Category: Deep Sky

Well, I needn’t have worried about the clouds. On the West side of the island I had six clear nights out of six (Dan had seven but I was down on the coast that night under the inversion layer!). Six solid nights of getting to bed at 3 & 4 in the morning, getting up at 9 and wandering up volcanoes. At least I got the odd nap during the afternoons.

All of this didn’t leave any time for image processing or blogging so I have a fair backlog to get through. I’ve started with the image I first posted on the Breckland Astro forum. I’ve now removed the colour cast and some of the light pollution gradient although this wasn’t entirely successful.

It’s not everyday that a supernova explodes in a nearby galaxy, especially not as close as M51 (27 million light years). The last one in this particular galaxy was in 2005. Of particular interest this time is that M51 is one of the most imaged objects in the night sky so there’s a lot of possibility for examining it’s evolution before it’s official discovery.

So, here’s Dan & my picture from last night with the supernova marked:

One of the surprising things about the night sky is the number of galaxies out there that can be photographed with a humble 70mm refractor and Canon DSLR camera. With my last few outings concentrating on Ursa Major for this clear night I decided upon the Virgo cluster and the Markarian Chain.

The Virgo galaxy cluster contains upwards of 1200 galaxies and it’s centre is 53 million light years away. Together with the Local Group it forms a small part of the Local or Virgo Supercluster.

The Markarian Chain is named after the astrophysicist who first noticed their common motion in the 1970s.

Imaging these galaxies was surprisingly difficult after the large spirals in Ursa Major. Being further away, they’re smaller and fainter and there’s a lack of bright stars in the near vicinity which makes locating them harder. Fainter means that more exposure is required to bring them up out of the background noise. Being close to the Celestial Equator also means that the polar alignment is rather more critical than I’ve become used to. While I did make a correction to the mount after the first couple of images it still required more refinement.

For these images I put the focal reducing William Optics field flattener on the camera and to compensate for the increased photographic speed of this combination reduced the exposure time to 4 minutes per frame. The focal length is reduced to 336mm. I’m not entirely happy with how this focal reducer works just yet; some more experimentation is required. It may be that it isn’t an ideal combination with this telescope.

I’m not going to even try and label all the galaxies in this image.

Telescope: WO 70mm Zenithstar with FF3
Camera: Canon 350D
Frames: 18x 240 second

After my last picture of M101 I was anxious to see what a little more exposure would do for the image. I got my chance at the beginning of April with a beautiful clear night and exposed 15x 5 minute frames of this area. Leaving the camera on ISO 800 was probably a mistake as it causes the brighter stars to lose colour. In future, I will probably stick to ISO 400 for this length of exposure.

The bright smudge to the right of M101 is NGC 5474, a gravitationally bound near neighbour of M101 and a disrupted dwarf spiral galaxy. The core is offset by it’s interaction with the larger galaxy.

After an abortive effort to find NGC 2403 in Camelopardalis (it’s very difficult to locate things when there are no bright stars in the vicinity and you’re lying on your back peering through a reflex sight) I switched to M109 in Ursa Major. This is conveniently located next to gamma UMa (Phad). The sky conditions were superb and a 5 minute test exposure showed little trailing so I went ahead and shot 1.5 hours worth at ISO 800 with the Canon 350D.

This was the first time I’d attempted 5 minute exposures on the Astrotrac at a focal length of 420mm using just the polar scope but it worked very well. If I’d had more time then it would have benefited from a drift alignment but that’s still a whole new learning curve.

Looking at the resulting image in Aladin I identified galaxies down to mag 16 (UGC 6840) and some MGC galaxies as faint as mag 17 although I haven’t included these on the image here. Not too bad for a 70mm refractor.

Before the clouds rolled in on Thursday night I was experimenting with some techniques for polar aligning my Astrotrac and finished off with 6 2 minute exposures of M101 in Ursa Major. One of the nice things about wide field photography is that you never know what else is going to turn up in the picture and this whole area is rich in galaxies and I’ve annotated the picture with the names of the brightest.

Telescope: ZenithStar 70
Camera: Canon 350D
Exposure: 6x 2 minute

At the front of Leo is the bright barred spiral galaxy, NGC 2903. Dan Self has recently produced an image using the 20″ (http://farawaythings.blogspot.com/2011/02/lions-head-galaxy.html) but I decided on the slightly different approach of using longer 3 minute ISO 800 exposures. Thin high cloud caused some problems with the auto-guider and I found myself using 5 second guide exposures which is a little long for this telescope. This has resulted in rather poor shaped stars.

The longer exposures have helped to reveal the faint arms of the galaxy and the fainter background galaxies but there’s a lot more noise in this picture as a result of only gathering 11 frames. The next opportunity I will try and increase my collection to see what improvements this will bring.

If there’s one thing I’ve learnt about image processing, it’s that there always something else to learn. On occasion, it’s worthwhile going back to some older images to see if they can be reprocessed to better effect. My original post on NGC 4038 was here: http://blog.andrewluck.me.uk/2009/02/28/the-antennae-galaxies. The widefield image suffered a lot from colour noise and this was due to the dark frames used not removing some of the brighter pixels and overcompensating for others resulting in black dots on the luminance frames and colour spots on the RGB frames.

When re-processing, I only calibrated the colour images, relying on the stacking process to average out the noise on the luminance. Then I manully removed the brightest colour dots which remained. Once the combine had been done I used GradientXterminator to remove a lot of the background noise.