Messier 51 (M51), better known as the Whirlpool Galaxy, is an iconic grand-design spiral galaxy located in the constellation Canes Venatici.
The Whirlpool Galaxy has an apparent magnitude of 8.4 and lies at an approximate distance of 23 million light years from Earth. It has the designation NGC 5194 in the New General Catalogue.

M51’s smaller companion (right of M51), NGC 5195, is a dwarf galaxy that is interacting with the Whirlpool Galaxy.

This is my first attempt at processing NASA Hubble Legacy Archive Data.

We have had such terrible weather on moonless nights these past two months I have not been out once; so to keep my hand in I turned to the HLA Data files.

Make no mistake. This is not a trivial exercise; and many hours are required to make a half way presentable image.

Data acquisition: Hubble Legacy Archive, NASA
Data processing: Doug Griffith
Image: RGB image per colour mapping below
Colour mapping:
.... red channel: 658 μm Hubble + 814 μm Hubble
.... green channel: 565 μm Hubble
.... blue channel: 435 μm Hubble
Processing software: ESA/ESO/NASA Fits Liberator 3, Pixinsight; and Photoshop CS6

The processing involves taking 3 greyscale images that were shot with different filters by the Hubble Space Telescope, stretching them in Pixinsight; then assigning the different filter wavelengths to red, green and blue channels; (sometimes using Pixel Math to combine and/or strengthen/weaken the intensity of the channels); and then combining them together into a single RGB image. The RGB colour image is further processed in Photoshop