M17 - Swan Nebula - Sagittarius

Object Data: Messier 17, (NGC 6618) Swan or Omega Nebula, is a very bright nebulous area at the northern extreme of Sagittarius, close by the border with Serpens Cauda. It is also variously known as the Swan Nebula (from its inverted appearance), the Omega Nebula, or the Horseshoe Nebula. The central bar-like mass of emission nebulosity has a very high surface brightness and is easily seen in binoculars. The outer parts are much fainter and extend over a comparatively wide area. Unusually there are no obvious bright stars fuelling the vigorous ionization of gases, but it has been suggested that there are hot stars embedded deep within the nebulous region. M17 is about 5,000 light years distant. It was probably first seen by the Swiss astronomer P.L. de Cheseaux in the spring of 1764 and was found and catalogued independently by Charles Messier in June of the same year. Date: 15/06/02 (R Luminance only: G, B were from 14/06/02) Location: Southern France Conditions: calm, transparency=8, seeing=9 (zero Jetstream) Optics: RCOS Ritchey-Chretien 12.5" f/9 working at f/6.7 with AP x.75 focal reducer. Mount: AP 900 GTO on Portable Pier Camera: SBIG ST-8E / CFW-8 Guiding: Integral ST-8E guiding chip controlled via MaximCCD Exposure: High resolution R/RGB (no binning): 40/40:40:60 minutes Processing: Image acquisition, calibration, combining, and DDP were applied using Maxim DL. Deconvolution was applied using AIP. Registration of Luminance and RGB images done using Registar, with and final image adjustments applied in Photoshop. Notes: The notes from the M16 image apply here also: This was an R/RGB more through necessity than choice (causing the image to appear a more monochromatic red than it should be). Explanation: I already had a full high resolution RGB set of M17 from the night of the 14th June, however the seeing was rather poor. Subsequently the night of the 15th June had excellent seeing and my preference would have been to re-image the entire RGB sequence, however there was time for only one such image, so I chose to re-image the Red frame and use it for the luminance. Although a compromise, this resulted in a far better image overall than using the RGB set from the night of the 14th. Note that broadband (unfiltered) luminance images could not be used owing to the problem of Spectral Dispersion at Low Elevation.