Crab Nebula, NGC 1952 (M1) - polarised
Tags: Crab Nebula, Crab, Nebula, NGC 1952, M1
The image was made from four plates taken on the Palomar (Hale) 5m telescope between August 1956 and January 1964, using a filter that excluded the nebular emission lines, allowing only the highly polarised synchrotron light to be recorded. Each of the four images was taken with a Polaroid filter rotated 45 degrees (i.e. 0°, 45°, 90°, 135° and 180°). One of these plates was contact copied to make a positive film copy, and this positive aligned in turn with each of the three remaining images, revealing the difference between them. These three, black and white difference images were captured on film and used as the red, green and blue channels to make a colour negative which made the photograph seen here.
All the work was done photographically, in pre-computer analogue mode, but the image has subsequently been digitally remastered from the monochrome photographic derivatives. These are 'false colours' which is not meant to imply something underhand, rather colours used to make visible something that could not be seen through a telescope, even with Polaroid. They thus represent the invisible, inflated and evolving magnetic field of a star that exploded almost 1000 years ago. The more you look, the more symmetries you see.
A description of the way the image was created is in an article by Malin and Pasachoff in Sky and Telescope, Vol 86, July 1993 (p43–46).
Credit: David Malin
"Copyright (or ©) Malin/Caltech/Pasachoff