M101 is one of the most well-studied galaxies to date.  It is
extremely high surface brightness owing to star formation
which is pervasive throughout the entire disk.  Some very large
H II regions can be found at large radii from its center, and
this is somewhat unusual.  The large number of massive stars
now forming in M101 has made it an excellent case for study in
the Ultraviolet, where faint extensions beyond the optical limit
of the galaxy can be seen.  High resolution photos of the center
of M101 indicated it to be composed of several UV bright knots which
are probably dense clusters of young stars.   This exposure was
taken in the blue, again with reimaging optics on a 52-inch telescope.
The exposure time was 30 seconds.

Note in the original Messier list, M101 and M102 are the same object.