| Messier 29 | |
|---|---|
 Open cluster Messier 29 in Cygnus, conventionally taken (as looking at the object on the southern horizon). Very broad reddish nebulosity is noticeable to the west. | |
| Observation data (J2000epoch) | |
| Right ascension | 20h 23m 56s[1] |
| Declination | +38° 31′ 24″[1] |
| Distance | 5,240 ly (1,608 pc)[2] |
| Apparent magnitude (V) | 7.1[3] |
| Apparent dimensions (V) | 7.0′ |
| Physical characteristics | |
| Mass | 580–1,090[1] M☉ |
| Estimated age | 13.2 Myr[4] |
| Other designations | M29,NGC 6913,Cr 422, OCl 168[5] |
| Associations | |
| Constellation | Cygnus |
| See also:Open cluster,List of open clusters | |
Messier 29 orM29, also known asNGC 6913 or theCooling Tower Cluster, is a quite small, brightopen cluster ofstars just south of the central bright starGamma Cygni of a northerlyzone of the sky,Cygnus. It was discovered byCharles Messier in 1764, and can be seen fromEarth by usingbinoculars.
M29 is well within the several degrees of the arms and bulge of theMilky Way. It is at least many hundreds of light years short of the yardstick distance to theGalactic Center, as is between 4,000[6] and 7,200light years away.[7] A 1998 popular work gives a value within this range.[a][8] Data from Gaia EDR3 gives a parallactic distance of about 5,240 light years.[2] The uncertainty is due to poorly known absorption of the cluster's light. Itsextinction greatly is from faint surrounding nebulosity and other foregroundinterstellar matter of this cross-section of thespiral arms (seeOrion–Cygnus Arm, which is our local arm).
According to the Sky Catalogue,[6] M29 is included in the Cygnus OB1 association, and the radial velocity component of three-dimensional motion, by default factoring in the solar system's current trajectory, is one of approaching at 28 km/s (noted, thus, as negative). Its age is estimated at 10 million years, as its five hottest stars are allgiants of spectralclass B0. Kepple and his associates give the apparent brightness of the brightest star as eighth magnitude of in the mid-wavelength (and frequency)"visual" band.[8][b]
The cluster'sabsolute magnitude is estimated at −8.2, a luminosity of 160,000 solar luminosities (L☉). The linear diameter was estimated at only 11 light years. Its Trumpler class is III,3,p,n (as it is associated with nebulosity), although Götz gives, differently, II,3,m, and Kepple gives I,2,m,n.[8] The Sky Catalogue lists it with 50 member stars;[6] earlier Becvar estimated 20 members.
North of 47 degrees north, the cluster is for part or all of the day above the horizon. It can be made out inbinoculars in a good sky. In telescopes, lowest powers are best. The brightest of its stars form a "stubbydipper", per Mallas. The four brightest stars form a quadrilateral, and another set a small triangle just north of the northernmost of the four. It is often known as the "cooling tower" due to its resemblance to the hyperboloid-shaped structures. A few fainter stars are around them, but the cluster appears quite isolated, especially in smaller telescopes. In photographs, many faint Milky Way background stars appear.
Messier 29 can be found quite easily as it is about 1.7 degrees south[c] ofGamma or 37 Cygni (Sadr). Angularly close, and almost certainly nearby in space, is diffuse nebulosity.
The especially hot binary Wolf–Rayet starWR 143 (WC4+Be) (HD 195177) can be found near this cluster.
