The Coma Pinwheel occupies an area of 5.4 by 4.7 arc minutes of apparent sky, which corresponds to a linear diameter of 85,000 light years. It is one of the brighter spiral galaxies in the Virgo Cluster and appears almost face-on, which makes it a popular target for both professional and amateur astronomers.
The galaxy can be seen in small telescopes, but only appears as a dim ball of light with a brighter centre. 8-inch telescopes reveal a hazy patch of light with a more clearly defined centre. 10-inch telescopes begin to hint at the spiral structure under good conditions, and larger instruments reveal the galaxy’s dust bands and other details.
Messier 99 can be found 7 degrees east of the bright star Denebola in Leo or just under a degree southeast of the magnitude 5.1 star 6 Comae Berenices, which lies 0.5 degrees east of the edge-on spiral galaxy Messier 98. The best time of year to observe M99 and other galaxies in the Virgo Cluster is during the spring.
M101 - Supernova and Pinwheel Galaxy - Deep Sky Videos
June 7, 2012
Messier 99: Coma Pinwheel - Messier Objects
August 28, 2015