M51, Whirlpool Galaxy
The Hubble image was created from HST data from proposal 10452: S. Beckwith (STScI), R. Kennicutt Jr. (University of Arizona), and H. Bond, C. Christian, L. Frattare, F. Hamilton, Z. Levay, M. Mutchler, K. Noll, and T. Royle (The Hubble Heritage Team, STScI).
Note: High level science products (combined and mosaiced fits files for each filter) are available at: http://archive.stsci.edu/prepds/m51/
F435W (B), F555W (V), F658N (Halpha + [N II]), F814W (I)
This image is a composite of many separate exposures made by the ACS instrument on the Hubble Space Telescope. The color results from assigning different hues (colors) to each monochromatic image. In this case, the assigned colors are:
Blue: F435W (B)
Green: F555W (V)
Red: F658N (Halpha + [N II]) + F814W (I)