Messier 24 (NGC 6603): Small Sagittarius Star Cloud

As you explore the lower summer southern skies near Sagittarius and the heart of our galaxy, you’ll discover breathtaking regions teeming with star clusters and nebulae. Unfortunately, those of us in the mid to higher northern latitudes may have to navigate around neighborhood trees to see all these wonderful objects. The good news is there are a fair number of nice clusters and nebulae in the upper reaches of Sagittarius and Scorpio, which gives us a better shot at seeing these southern gems.

Messier 24 is not a traditional astronomical object like a nebula, star cluster, or galaxy. Instead, it is a region within our Milky Way galaxy that is densely packed with stars, making it appear like a stunning celestial cloud. In his famous Celestial Handbook, Robert Burnham, Jr. mentions how there has been much confusion in the astronomy community to even identify the exact classification for this area.¹

What makes Messier 24 truly special is that it serves as an “intergalactic window” to distant regions of our galaxy. The dark, obscuring dust and gas that usually fill the plane of the Milky Way are almost absent in this region, allowing us to glimpse deeper into the galaxy’s core. This characteristic gives us the rare opportunity to peer through a cosmic keyhole, so we have a unique chance to study the obscured regions of the Milky Way. Take note, too, that this region is huge in the sky. According to NASA, M24 covers an area of 8 full moons!²

Charles Messier first recorded M24 on June 20, 1764, the same night he recorded M23.

My Observations

After sketching Messier 23, I quickly looked at the star map to see M24’s location. To my surprise, M24 was centered in a narrow opening between two Douglas Firs. Not knowing the area well, I started with the 25mm eyepiece, which was overflowing with stars, so I bolted over to my kit and pulled out the 32mm. Still, a cloud of stars spread past the glass. Back to the kit again, I pulled the widest eyepiece: my 40mm. I fit the 40 into the scope and started sketching. Five minutes later, the stars started dimming as they fell behind the tree limb. I hope someday I may have a better view of this rich summer sky.

Key Stats

Constellation	Sagittarius
Best Viewing	Summer
Visual Magnitude	+5.50
Absolute Magnitude	-3.49
Distance from Earth	26,000 ly
Diameter	2000 ly
Apparent Size	29 arcmin
My Viewing Grade	B+
Designations	M24, NGC 6603, IC 4715, ESO 591-1, Milky Way Patch

Historical Observations

June 20, 1764, observation by Charles Messier

“Cluster on the parallel of the preceding M23 & near the end of the bow of Sagittarius, in the Milky Way: a large nebulosity in which there are many stars of different magnitudes: the light which is spread throughout this cluster is divided into several parts; it is the center of this cluster which has been determined.”³

Sources

The banner photo of M24 is a cut-out adaptation of photo by Roberto Colombari and is licensed under the Creative Commons Attribution-Share Alike 4.0 International license. Source here.

¹ Burnham, R. (1978). Burnham’s Celestial Handbook: An Observer’s Guide to the universe beyond the solar system. Dover Publications.

² NASA. (n.d.). Messier 24: Sagittarius star cloud. NASA. https://science.nasa.gov/messier-24-sagittarius-star-cloud

³ Guy McArthur, H. F. (n.d.). Messier 24. http://www.messier.seds.org/Mdes/dm024.html

Sketches by Wayne McGraw