Giant galaxies were not assembled in a day. Neither was this Hubble Space Telescope image of the face-on spiral galaxy Messier 101 (the Pinwheel Galaxy). It is the largest and most detailed photo of a spiral galaxy beyond the Milky Way that has ever been publicly released from Hubble. The portrait is actually composed from 51 individual Hubble exposures, in addition to elements from images from ground-based photos. The final composite image measures a whopping 16,000 by 12,000 pixels.