Messier 100 (Coma Berenices)
The grand design intermediate spiral galaxy Messier 100 (NGC 4321, Mirror Galaxy) in the constellation Coma Berenices
Fig. 1 - One of the brightest and largest galaxies in the Virgo Cluster: The spiral galaxy Messier 100 in Coma Berenices, photographed with an 8-inch f/4 Newtonian reflector on a ZWO AM5 mount.
| Object name: | Constellation: | Coordinates: | Apparent size: | Visual brightness: |
|---|---|---|---|---|
| Messier 100 (NGC 4321) | Coma Berenices | 12h23m / +15°49' | 7.4' × 6.3' | 9.3 mag |
Messier 100 (NGC 4321) is a grand design spiral galaxy with well-defined, prominent spiral arms in the constellation Coma Berenices. With a diameter of about 150,000 light-years, Messier 100 is slightly larger than our Milky Way and is estimated to contain several hundred billion stars.
The galaxy lies at a distance of roughly 55 million light-years and is a member of the Virgo Cluster, one of the nearest large galaxy clusters. Like most spiral galaxies in the Virgo Cluster, Messier 100 is located in the outer, less densely populated regions. Among the spiral galaxies in this cluster, it is one of the brightest. In the same field of view are several neighboring galaxies, including NGC 4312, NGC 4322, NGC 4328, and IC 783 (see annotated image). The Virgo Cluster contains at least 1,300 galaxies and likely more than 2,000. It lies in the direction of the constellation Virgo, with its center located about 54 million light-years from the Milky Way. The spiral structure of Messier 100 is rich in gas and dust and shows numerous active star-forming regions, particularly along the spiral arms. In images, these regions often appear as bluish knots where young, hot stars are forming. In addition, Messier 100 features a prominent central bar structure, which likely plays an important role in funneling gas toward the galactic center.
Several supernovae have been observed in Messier 100, including SN 1979C, which has been extensively studied over many years. Messier 100 was discovered in 1781 by Pierre Méchain and was shortly thereafter included in Charles Messier’s catalog.
Technical Details:
Exposure time: 5h 6min (102x3min)
Gain: 0
Date: March 19/20, 2026
Processing: Astro Pixel Processor (APP) and Photoshop
Calibration: Darks, flats, and bias
Equipment:
Cooled ASI 2600MC Pro camera, TeleVue Paracorr Type II coma corrector, 8" f/4 "ONTC" Newtonian telescope, ZWO AM5 Strain Wave Mount, ZWO OAG-L off-axis system, ASI 174MM Mini guide camera, ASIAIR Plus
Fig. 2 - Labeled image of Messier 100.
Fig. 3 - Finder chart for Messier 100. Copyright 2026 'The Mag-7 Star Atlas Project', www.siaris.net.