M13 was first described by Edmond Halley in 1714, but it is visible to the naked eye in dark skies so was probably seen by others over the centuries. Charles Messier catalogued it as number 13 on 1st June 1764. It is some 25,000 light years away in the constellation of Hercules and subtends an angle of about 20 arc-minutes which corresponds to a real diameter of about 150 light years.
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M13 captured with my ST80 refractor. This telescope has a focal length of 400 mm giving it a field of view of 31 x 23 arc-minutes. The picture was taken using my modified Toucam 840K; the original picture was far too blue, so the background was adjusted to black by use of the smart colour-balance feature of PhotoImpact. This gave pictures very similar to, but slightly better than those in which the colours were balanced in RegiStax or manually in Photoshop. The bright star on the left-hand edge of the picture is HD150998 of magnitude 6.83 and is 16' 43" from the centre of the cluster. If the picture is too dark on your monitor, move your mouse over it to see one with the gamma increased to 2.0. Date and Time: 1st May 2007 21:12 UT Camera: Modified Toucam 840K Telescope: Skywatcher ST80 (focal length 400 mm) Capture: K3CCDTools. Low gamma, exposure 25 sec, 52% gain Processing: K3CCDTools. 51 frames stacked, unsharp mask 3 pixels, factor 150 |
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And here captured with my LX200 with a 0.33 focal reducer fitted giving it a focal length of 800 mm and a field of view of 15.5 x11.5 arc-minutes. It was taken with a raw-modified Atik (monochrome) camera and the blue filter from an Astonomik LRGB set. Date and Time: 1st May 2007 22:41 UT Camera: Atik 1-HS Telescope: LX200 with 0.33 focal reducer (focal length 800 mm) Capture: K3CCDTools. Low gamma, exposure 12 sec, 100% gain Processing: K3CCDTools. 15 frames stacked, histogram 20-170, unsharp mask 3 pixels, factor 150 |
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