Object data: NGC 253 is a large magnitude 7 galaxy in the constellation of Sculptor. It has a remarkable amount of structure in both the core and arms, and the complexity of the dust lanes is such that it is difficult to discern a spiral pattern. It is estimated to be approximately 10 million light years distant and is one of the closest galaxies beyond our local group.
Date: 18/12/01, 19/12/01
Location: Southern France
Conditions: 18/12/01: calm, transparency=8, seeing=7/8 // 19/12/01: calm, transparency=9, seeing=9
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-8E integral guiding chip controlled by MaximCCD
Exposure: LRGB: Luminance: 18/12/01: 7x10 minutes; 19/12/01: 6x10 minutes; RGB: 10:10:20 minutes binned 2x2
Processing: Image acquisition and initial processing was done using Maxim DL, subsequent processing was done using Registar and Photoshop.
Notes: It's practically impossible to image NGC 253 with any quality from the UK (maximum elevation 13 degrees) so I tend to focus on such objects when in southern France. Even from southern France it is quite a challenge (maximum elevation 20.8 degrees) - average elevation during these exposures was about 19 degrees. It's very hard to avoid some degree of misguiding at this elevation owing to air turbulence, hence star images and resolution have suffered. Also notice a significant amount of blue extinction owing to the low elevation! Conditions on 19/12/01 were superb - had I used only those images the result would have been sharper but in the end I opted for the lower noise and greater dynamic range offered by combining the images of 18/12/01, at the expense of resolution.