The Pleiades (M45)

All Images Copyright Steve Cannistra

Magnitude:  1.6
Distance: 380 light years
RA: 3h 46m 31s
Dec: 23 degrees 57' 36"

The beautiful Pleiades open star cluster (M45, the "Seven Sisters") has been recognized since antiquity, with the oldest recorded observation being approximately 1000 years BC.  Within this cluster, it is possible to resolve between 7-11 stars with the naked eye, depending upon seeing conditions (and eyesight!).  Through the telescope, the cluster is known to contain about 500 stars that are gravitationally bound to each other.   The age of this cluster is estimated to be about 65 million years old, meaning that it was "born" around the time of the dinosaur extinction.  The beauty of this cluster is due to the impressive amount of blue nebulosity that surrounds many of the stars, most notably Merope (surrounded by the brightest reflection nebulae of this group, NGC 1435).   In contrast to emission nebulae, the blue color of this nebula is due to reflected light from nearby young stars.  During visual observation, there is a hint of nebulosity in a small scope such as an 8" SCT, although the full extent can only be observed in longer exposure photos such as this one.  Please click on the following link to observe a higher resolution image.

Photographic Details:

Dates:  September 29, 2003 (Merope region) and October 6,  2003 (5 additional regions to complete the mosaic)
Scope:  LX90 at f6.3, Lumicon OAG
Autoguider:  SBIG STV with e-finder
Camera:  Canon 10D
Filter:  IDAS LPS
Exposures:  30 exposures x 6 to 9 minutes each at ISO1600.  Total exposure time 3.5 hours.
Temperature 49 degress F; average transparency; average seeing; wind minimal (September 29).  Temperature 39 degrees F on October 6.
Post-processing:  This represents a mosaic of a total of 6 different sections of M45 (each section is an average stack of 5 frames).  The frames for each section were processed as follows:  raw conversion, adaptive dark frame calibration, alignment, autograding, min/max excluded averaging, and background compensation done in ImagesPlus; levels and curves adjustment in Photoshop; final smoothing done in Pleiades SGBNR software.  Mosaic was constructed in Photoshop using the technique described by Rob Gendler.  Total processing time was approximately 20 hours over a period of 3 days.

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