Open Cluster NGC 7789

All Images Copyright Steve Cannistra

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Magnitude:  6.7
Size: About 16'
Distance: ?
RA: 23h 57m 0s
Dec: 56 degrees 43' 59"

NGC7789 was identified by Caroline Herschel and is one of the oldest open star clusters known (about 1.6 billion years old).  It sits in Cassiopeia amidst many stars of the Milky Way galaxy, although the compact nature of this open cluster makes it easy to identify.  It contains at least 1000 stars of varying ages, with several older, red giants being easily visible.  I was not prepared for the sheer number of stars in this field, which either add or detract from the beauty of the central star cluster, depending upon your point of view.

Photographic Details:

Date:  January 10, 2005
Takahashi Sky 90 at f4.5 with field flattener/focal reducer, on the G11 Losmandy Mount.  I made a circular rim out of PVC tubing which fitted over the dew shield of the Sky90 and permitted placement of an elastic band to form an "X".  This created the star spikes shown above for the brighter stars.  A photograph of this device is shown here (this could also be accomplished with kite string or fishing line).
Autoguider:  SBIG STV with e-finder.
Camera:  SXV-H9
Astronomik Type II R, G, B, plus clear filter set.
Exposures:  L:R:G:B.  8 x 2' for Luminance (clear filter); R, G, and B (5 x 3' each), all unbinned.
Conditions:  Temperature 36 degrees F; average transparency; average seeing; a bit breezy.
Post-processing:  No darks, flats, or bias frames used.  Alignment and Min/Max Excluded combine done in ImagesPlus.  DDP was performed in ImagesPlus (IP).  Subsequent levels and curves adjustments in Photoshop CS (16 bit format).

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