Category: Galaxy

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.

Galaxies tend to come in groups, and, after the local group this is the next nearest with M81 being the primary galaxy at a distance of 12 million light years. Also in this picture are other members of the group; M82 and NGC 3077. With a more aggressive screen stretch it’s also possible to detect the background galaxy UGC 5336 just to the left of M81.

As Wednesday evening was clear and still, I took the opportunity to gather 2 and a half hours worth of 3 minute exposures at ISO 800 with my ZenithStar 70 and Williams Optics field flattener. Bias and flat frames were also used in the image processing but not dark frames.

I was originally going to post an image of this galaxy that I took in Yorkshire, but the sub-frames were only 1 minute in length and the galaxy lacked detail in the fainter regions. This is the result I took from home using 180 second exposures. Later images in the series trailed due to my using an unbalanced setup but results have been much improved by replacing the Manfrotto 410 head with an Astrotrac wedge.

Telescope: Zenithstar 70 with WO FF III
Exposures: 13 x 180 seconds ISO 800. Flats and darks not used.

The Yorkshire sky had a much better southern horizon than I get at home so one of the things I wanted to image was the Milky Way. Unfortunately, I was plagued with cloud in this direction so all I managed was 2 3 minute exposures at ISO 800 with the 18-55 Canon lens. Even these frames had some cloud reflecting the sodium lighting of the towns to the south but the results show promise with a dark sky down to the horizon.

Notice that the Coathanger stands out well in this picture, almost dead centre.

I’ve resisted imaging M51 for a while now with the feeling that the world doesn’t need yet another picture. However, my recent  rough and ready image and Dan’s work convinced me that this really is one of my favourite night sky objects. So, I gathered 60 minutes of exposure time on GRAS-3 in 5 minute sub-frames. The results, while nice to look at lacked some definition in the finer detail and I found myself wondering what rather more exposure time would do for the image. The following night I gathered another 60 minutes and, when added in, the difference was stunning. Detail in the dust lanes that had been rather blurred before leapt out of the screen and this was before any additional processing had been done.

I made several attempts at processing the results before settling on this image. I’ll probably return to this in the future and try and enhance the tidal tail of stars that have been swept out by this galactic close encounter.

While the Leo Triplet is well known, there is a fourth member of this group a little further away and it’s depicted here in this 2.5 degree field.

All three galaxies in the main triplet show signs of interaction and the group as a whole is listed in Arp’s Atlas of Peculiar galaxies as ARP 317. M66 is also listed separately as ARP 16 (Spiral with detached segments). Distance to the group is about 33 million light years and measuring this picture shows that the nuclei of M65 & M66 could be as close together as 192,000 light years. By comparison, our nearest galactic neighbour is M31, Andromeda at 2.5 million light years.

The image is a stack of 15x 3 minute exposures at ISO400 using the WO Zenithstar  70 with a Sky Watcher field flattener.  Some trailing is apparent and the individual frames could use rather more exposure time and/or a higher ISO setting.

There’s been rather a trend on this blog towards pairs recently and to continue this theme here’s an image of NGC 4567 & NGC 4568, sometimes known as the Siamese Twins. This pair of interacting galaxies are part of the Virgo cluster and for some years were considered a line of sight pairing as there’s no visual evidence of interaction.

This image is the result of a stack of 14 five minute frames taken on GRAS-4 over two nights.

This picture was taken with the Canon 75-300 zoom before I bought the Williams Optics refractor. The focal length is 190mm and this image is about one quarter of the original field. Sixteen 3 minute exposures were combined and despite the short exposure time and mis-shapen stars some detail is visible in the galaxies. Also in the frame are two more smaller galaxies, NGC 2976 is on the right and NGC 3077 is at the bottom.

p>Whilst spending the weekend with my Dad, we stopped off at Astronomia in Dorking, Surrey. There on the shelf was a Williams Optics 70mm Zenithstar. I’ve been looking for something small and light to replace the Canon zoom lenses on the AstroTrac and this fitted the bill exactly. Having parted with some money, I took it home and contrary to known astronomical principles, the following night was clear!

First target, M51. This being a first attempt I wasn’t too sure what to expect at the longer focal length and the tracking wasn’t perfect so I finished the run with just 5 images of 3 minutes each. With the Canon 350D attached, the 420mm focal length yields 3.14″/pixel.

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