Andrew’s Astronomy Blog

Whilst at the Kelling star party I had a talk with Bernard from Modern Astronomy about cameras and specifically the Kodak KAF-8300 chipped models. I’d been thinking about a single shot colour for the astrotrac setup and the QHY9 looked a good match for a very good price. I placed an order and delivery was via Fedex within 2 days.

I’d had the idea in my head that the cooled colour CCD camera would be a low noise, high sensitivity version of the DSLRs I’ve been using but some test shots revealed that this isn’t entirely true. Initial pictures were a little disappointing and it wasn’t until I was reading an article on setting the offset and gain levels for the camera (http://www.stark-labs.com/blog/files/GainAndOffset.php#unique-entry-id-6) that the pieces fitted together and illumination dawned.

You can get surprisingly good pictures with short exposures on DSLRs by increasing the ISO rating. This is effectively increasing the gain and it’s not a free lunch. Noise is amplified as well and dynamic range is reduced. With the CCD, once you’ve calculated the optimal gain you set it and never alter it again. This level will be a lot lower than the DSLRs value and correspondingly longer exposures are required to fully exploit the increased dynamic range available.

With my Zenithstar 70mm Astrotrac mounted on a Manfrotto tripod I’m limited to 5 minute exposures without trailing so I picked a bright target for a test. M31 is ideally placed for this  at the moment and here’s the result resized to about half the original.

12 5 minute exposures

Zenithstar 70mm

William Optic FFIII field flattener

Friday night was the first opportunity I’ve had to take some pictures of this. Thursday night was also clear but I was busy imaging comet Garradd again, this time passing close to the Coathanger cluster.

Using the club’s ATIK on the 20″ we took 41 30 second exposures binned 3×3 and also 3 each of red, green and blue binned 6×6. This really wasn’t enough colour frames and after a lot of effort I gave up trying to get a colour image and just stacked the luminance frames.

Sn2011fe is a type 1a supernova a mere 21 million light years away.

One of the treats of the trip to AstoPalma was the chance to use the 40cm relay cassegrain. This is an interesting design where all the optical surfaces are spherical and therefore easy to make but, there are rather more of them than in a conventional design. The focal point is inside the telescope tube and a small lens is used to ‘relay’ this point back to the eyepiece. Details of the the optical design are here: http://www.astropalma.com/Cass_Relay_Componentes_p.jpg

The main camera on this telescope is an SBIG ST8XE using the SBIG Adaptive Optics unit for guiding. Limited time meant that we only acquired a single 10 minute frame for each colour but we did get 4 luminance frames of the same length. The result of this was some pretty bad colour artifacts which required judicious use of the spot healing brush in PhotoShop. So, the result is here.

Edit: Adjusted the colour balance to make the spiral arms a little less green.

Living within a spiral galaxy gives us the chance to get an up close view of the dust clouds that fill the inter-stellar space in the spiral arms. If it wasn’t for this dust obscuring the starlight from millions of stars then our night sky would look very different.

This image is a wide-field view of the area around Cygnus. Six exposures of 3 minutes each at ISO 800 and f/3.5 with my Sigma 10-20mm zoom.

One of the main attractions of La Palma was it’s views of the Milky Way. It’s southerly latitude opens up views of our galaxy’s centre that just aren’t possible from the UK. This picture is a mosaic of two images taken with the Sigma 10-20mm  set at 10mm on my Canon 350D. Each image is a stack of three 3 minute exposures at ISO 800 and f/3.5.

Cygnus and Lyra are at the top of the picture, with Scorpius and Sagittarius at the bottom.

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:

I’ve also put together an AVI with a previous image taken with one of the GRAS scopes which shows the supernova appearance clearly. This file is available here:

M51 movie

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  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