M24, also known as the Small Sagittarius Star Cloud, is a large naked eye expanse of stars, clusters, nebulosity and other objects located in Sagittarius. At mag. +2.5 and covering 1.5 degrees of sky, it's visible to the naked eye as a large detached part of the Milky Way. The object is a fantastic sight in binoculars and small telescopes. It's claimed that M24 has the densest concentration of individual stars visible, around a thousand, in a single binocular field of view. It should not be confused with the nearby Large Sagittarius Star Cloud which lies about ten degrees to the south.
The Small Sagittarius Star Cloud is not a true deep sky object but results from a rare alignment between the Earth and the centre of our galaxy. We would expect this region to be packed with interstellar dust, however by chance we are looking through a gap in the dust. As a result, many thousands of distant stars, clusters and nebulae are visible that would otherwise be obscured. Spatially, M24 covers a volume up to 16,000 light-years deep.
M24 can be found 7 degrees north and a little west of the top star of the bright teapot asterism, Kaus Borealis (λ Sgr - mag. +2.8). Positioned north of M24 is open cluster M18 and the Omega Nebula (M17). All three objects are visible in the same binocular field of view. Open clusters M23 and M25 are located a few degrees west and east of M24 respectively.
M24 was discovered by Charles Messier on June 20, 1764. It's best seen from southern or equatorial latitudes during the months of June, July and August.
Finder Chart for M24 - pdf format (credit:- freestarcharts)
M24 is a wonderful sight through 7x50 or 10x50 binoculars with many hundreds of stars visible in striking patterns. It's a showpiece object for binoculars and small telescopes owners. A part of the mystique of the cloud is lost in medium and large size scopes, since it's too large for the eyepiece field of view. Nethertheless, through a 200mm (8-inch) scope it's still a fascinating sight with hundreds of stars visible, intertwined with nebulosity and complex dust lines.
Dim open cluster NGC 6603 (mag. +11) lies within M24 and is sometimes incorrectly quoted as being the same object as M24.
M24 Data Table
| Messier | 24 |
|---|---|
| Object Type | Milky Way star cloud |
| Constellation | Sagittarius |
| Distance (light-years) | 10,000 |
| Apparent Mag. | +2.5 |
| RA (J2000) | 18h 17m 00s |
| DEC (J2000) | -18d 29m 00s |
| Apparent Size (arc mins) | 90 x 40 |
| Radius (light-years) | 300 |
| Age (years) | 220 Million |
| Number of Stars | >10,000 |
| Notable Feature | Fills a significant volume of space up to a depth of 16,000 light-years. |