Messier 100 (NGC 4321): A Grand Design Spiral in Coma Berenices

Few celestial objects rival the elegance of spiral structure like Messier 100 (M100), a grand design spiral galaxy nestled in the spring constellation Coma Berenices. Located approximately 55 million light-years away, it is one of the brightest and largest members of the Virgo Cluster. Discovered by Pierre Méchain on March 15, 1781 and catalogued by Charles Messier a month later, M100 remains a highlight for both amateur stargazers and professional astronomers.

A Showcase of Spiral Beauty

M100 is a nearly face-on barred spiral with beautifully defined, symmetrical arms rich in star-forming regions. These arms glow in blue tones from massive young stars and are interspersed with dust lanes and reddish nebulae, marking the ongoing stellar birth within.

Messier 100 | Credit: ESO/IDA/Danish 1.5 m/R. Gendler, J.-E. Ovaldsen, C. C. Thöne and C. Féron

For backyard astronomers, M100 presents different levels of detail depending on equipment and conditions. Through binoculars or a small telescope (3-4 inches), the galaxy appears as a faint, round fuzzy patch with a slightly brighter center. Medium-sized telescopes (6-10 inches) under dark skies begin to reveal the galaxy’s oval shape and brighter nucleus, with the outer regions appearing mottled or uneven.

A Cosmic Pinwheel Worth Visiting

Messier 100 is a visual delight, although its faintness presents a challenge for backyard astronomers in capturing its beautiful light. Charles Messier would relate as we read his observation in his own words, as documented on Messier Objects:

“Nebula without star, of the same light as the preceding [Messier 99], situated in the ear of Virgo. Seen by M. Méchain on March 15, 1781. The three nebulae, nos. 98, 99 & 100, are very difficult to recognize, because of the faintness of their light: one can observe them only in good weather, & near their passage of the Meridian.”

My Observation

Date	April 26, 2025
Time	10:43 p.m.
Location	Tampa, FL
Magnification	~15x
Scope	Seestar S50
Exposure Time	16 minutes
Seeing	Average
Transparency	Average

As with several of my observations recorded on this night, I decided to use the small Seestar S50, since Florida’s high humidity made me reconsider setting up my 8-inch scope, which tends to fog up quickly. Next spring, when M100 is in a better position, I plan to spend more time on the galaxy, as my 16-minute exposure just barely brings out its color and arms.

Several years ago in Seattle, I attempted to sketch Messier 100 on multiple occasions, but to no avail due to the region’s light pollution. I did manage to glimpse a very faint smudge as I wiggled the scope, but I felt it wasn’t distinct enough to sketch. I hope to return to darker skies one day to give it another try.

Key Stats

Constellation	Coma Berenices
Best Viewing	Spring
Visual Magnitude	+10.1
Absolute Magnitude	-21.8
Distance from Earth	~55 million light-years
Diameter	~107,000 light-years
Apparent Size	~7.4 × 6.3 arcminutes
My Viewing Grade	B
Designations	M100, NGC 4321, UGC 7450, PGC 40153