M 39  8.08 2006
Image Capture Details

Optics:  Televue TV 60IS
Mount: Meade LX200
Camera: Canon 350XT
Filters: NONE

Focal Ratio:  F/6

Guiding: Meade DSI

Exposure:
11 X 45 Seconds = 8 Minutes
Time: 11:05- 11:13 PM EST
Location: Waldwick, NJ
Click image for
higher resolution
M39 is a very large but very loose open cluster, situated some 9 degrees east and a bit north of Deneb (Alpha Cygni). Its
distance is only about 800 light years, and it is of intermediate age (estimates between 230 and 300 million years). 30 stars
are proven members and contained in a volume of about 7 light years diameter. Its apparent visual brightness of 4.6
magnitudes (e.g., Sky Catalogue 2000.0, Uranometria 2000) corresponds to an absolute magnitude of -2.5, or an intrinsic
luminosity of 830 suns. Kenneth Glyn Jones gives its apparent visual brightness as 5.2 mag only, while Don Machholz has
estimated it at mag 5.4, in agreement with estimates quoted by Mallas/Kreimer, who also mention D.F. Gray's estimate of a
total visual brightness of 6.0 magnitudes.

M39's brightest star is of magnitude 6.83 visually, and of spectral type A0. All stars were found to be main sequence stars
in the Color-Magnitude Diagram (CMD), or Hertzsprung-Russell Diagram (HRD), with the brightest stars apparently just
before the point of evolution toward the red giant phase. The Sky Catalogue 2000.0 gives an estimated age of 270 million
years for this cluster - this is between the two determinations cited by Kenneth Glyn Jones of 300 million years by
Lohmann and 230 million years by Van Hoerner. M39 is approaching us at 28 km/s; its proper motion was given as 0.024"
per year in the direction of position angle 222 deg (by E.G. Ebbighausen 1940, according to Burnham).

1 - http://www.seds.org/messier/m/m039.html
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