Compass and Scale Image of M51
M51, Whirlpool Galaxy
About 31 million light-years (9.6 million parsecs)
This image is 3 arcminutes (20,000 light-years or 6,000 parsecs) wide.
The Hubble optical image was created from HST data from proposal 10452: S. Beckwith (STScI), R. Kennicutt, Jr. (University of Cambridge), and H. Bond, C. Christian, L. Frattare, F. Hamilton, Z. Levay, M. Mutchler, K. Noll, and T. Royle (Hubble Heritage Team, STScI/AURA). NICMOS observations were made with the HST proposal 10501: R. Chandar (University of Toledo), D. Calzetti (University of Massachusetts), R. Kennicutt, Jr. (University of Cambridge), M. Regan and B. Whitmore (STScI), and E. Schinnerer (Max Planck Institute for Astronomy, Heidelberg).
This image, which was obtained by aligning data from both the NICMOS and ACS detectors and dividing the NICMOS brightness values by the ACS values, was originally black and white. These brightness values were translated into a range of reddish hues. Such color "maps" can be useful in helping to distinguish subtly varying brightness in an image.