Object data: M108 (NGC 3556) is an Sc spiral galaxy with an interesting and complex structure located about 45 million light years distant in the constellation of Ursa Major. It has a visual magnitude of 10, despite which it is quite easy to spot in small telescopes. M108 was formally discovered by P. Mechain (Messier's assistant) on 19 February 1781. Messier gave this object a preliminary listing of 98 but it did not form part of his published catalogue at the time. It was classified as M108 and formally added to the Messier catalog in 1953 by O. Gingerich.
Date / Location: 06/04/00, 07/04/00: southern France
Conditions: 06/04/00: transparency=8/7, seeing=3/5. 07/04/00: transparency=6, seeing=6, v heavy dew
Optics: LX200 10" with GEG working at f/11.2 (lens removed)
Mount: AP 900 GTO on Portable Pier
Autoguiding: SBIG ST-4 tracking off-axis guide star with GEG.
Camera: Nikon F2 with Nitrogen gas purge into the film transport chamber.
Film: Kodak Ektapress Multispeed PJM-2 - gas hypersensitised.
Exposure: 06/04/00: 120 minutes, 07/04/00: 100 minutes
Enhancement: Two negatives were scanned using a Polaroid Sprintscan 35 Plus and digitally stacked in Picture Window, then further enhanced in Photoshop.
Notes: Two very different exposures comprise this photo. On 06/04/00 tranparency was excellent though seeing was very poor ('fuzzball' stars - about 5 arc seconds) whereas on 07/04/00 seeing was better (about 2.5 arc seconds) but transparency was poor. Also there was very heavy dew, leading to an 'aquatic' session (water everywhere). This latter problem cause slight film movement despite a high gas flow on the N2 purge, and slight dewing of the corrector plate despite a high dew zapper setting. Hence both exposures have enlarged stars, but for different reasons.