Object data: M101 (NGC 5457, Pinwheel Galaxy) is a large magnitude 8 galaxy located in Ursa Major. Photographically it is quite spectacular, however it has low surface brightness, making it difficult to observe in small instruments. It was discovered by P. Mechain in 1781 and catalogued by Messier in March the same year. Its distance is estimated at about 24 million light years. The diameter is approximately 90,000 light years and the total mass is estimated to be the eqivalent of 16 billion suns - about 10% of the mass of the Milky Way.
Date: 12/05/01
Location: Wiltshire UK
Conditions: Calm, transparency=8, seeing=6
Optics: RCOS Ritchey-Chretien 12.5" working at f/6.75 with AP focal reducer
Mount: AP 900 GTO on Portable Pier
Camera: SBIG ST-8E / CFW-8
Guiding: ST-4 via custom OAG (designed by Chuck Vaughn)
Exposure: LRGB: Luminance: 8x10 minutes; RGB: 10:10:20 minutes binned 2x2Processing: Image acquisition and initial processing was done using Maxim DL, subsequent processing was done using Registar and Photoshop.
Notes: Saturday 12th May was a superb day in the UK with transparent and totally cloudless skies. These conditions carried on into the evening with excellent transparency (for the UK) and seeing quite good at 2.3 arc seconds. My original intention was to re-collimate the optics that evening but I was so seduced by the sky conditions that I could not resist taking an image instead!
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