M 29
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M 29

February 18, 2005
Open Cluster M29 (NGC 6913), type 'd', in Cygnus

Right Ascension: 20 : 23.9 (h:m)
Declination: +38 : 32 (deg:m)
Distance: 4.0 (kly)
Visual Brightness: 7.1 (mag)
Apparent Dimension: 7.0 (arc min)

Discovered 1764 by Charles Messier.

M29 is a rather coarse and less impressive cluster, situated in the highly crowded area of Milky Way near Gamma Cygni, at a distance of 7,200 (most sources including Mallas/Kreimer and Burnham, and agreeing with early estimates or R.J. Trumpler 1930) or 4,000 light years (the latter from Kenneth Glyn Jones and the Sky Catalogue 2000.0). The Night Sky Observer's Guide by Kepple and Sanner gives a deviating value of 6,000 light years - the uncertainty due to inacurately known absorption of the cluster's light.

W.A. Hiltner of Yerkes Observatory, in 1954, found the light of its stars rather polarized by interstellar matter, which is apparently 1,000 times denser around this cluster and may absorb so much light that the cluster would be 3 magnitudes brighter if viewed "freely" or "in the clear"! Also in 1954, Harris reported irregular obscurations of cluster member stars (perhaps by passing interstellar dark matter through the line of sight).

According to the Sky Catalog 2000, M29 is included in the Cygnus OB1 association, and approaching us at 28 km/sec. Its age is estimated at 10 million years, as its five hottest stars are all giants of spectral class B0. The Night Sky Observer's Guide gives the apparent brightness of the brightest star as 8.59 visual magnitudes. The absolute magnitude may be an impressive -8.2 mag, or a luminosity of 160,000 suns. 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/Sanner gives I,2,m,n. The Sky Catalogue 2000.0 lists it with 50 member stars; earlier Becvar gave only the number of 20 members.

Open cluster M29 is one of the original discoveries of Charles Messier, who cataloged it on July 29, 1764.

This cluster can be seen in binoculars. In telescopes, lowest powers are best. The brightest stars of M29 form a "stubby dipper", as Mallas says it. The four brightest stars form a quadrilateral, and another three, a triangle north of them. A few fainter stars are around them, but the cluster appears quite isolated, especially in smaller telescopes. In photographs, a large number of very faint Milky Way background stars shows up.

M29 can be found quite easily as it is about 1.7 degrees South and little East of Gamma or 37 Cygni (Sadr). In the vicinity of M29, there is some diffuse nebulosity which can be detected in photographs.

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