M100 is one of the many galaxies in the Virgo Cluster though it lies within the boundaries of the constellation Coma Berenices. It’s about 55 million light years away. It’s a grand design spiral galaxy and is about 60% of the size of the Milky Way. M100 has an apparent diameter only about 1/5 the diameter of the full moon.
This field has a lot of other galaxies in it, marked in the image below:
Each circle represents a place where a galaxy is though it may not be visible in the image. it’s also likely there are other galaxies that are visible (though tiny in the image) that are not in the catalog used by the annotation software.
After M100, the largest galaxy (in the image, not necessary in absolute terms) is NGC 4312. It’s the edge on spiral toward the bottom of the frame just right of center. It’s also about 55 million light years away and in the Virgo Cluster.
This image has just under 60 hours of integration time and is an HaRGB image though the hydrogen alpha contribution is only minimally combined with the RGB data. For all the technical details see the astrobin version.