NGC 188,  Caldwell 1.  An open clusterHome

NGC 188 has the distinction of being the most northerly of the open clusters at a declination of 85° 20' North.  As such it is number 1 in the Caldwell catalogue which is ordered by declination.  Although nowhere near the galactic north pole (which is in Coma Berenices), the cluster is well above the galactic plane and further from the centre than is the Sun.  This means that it has not passed through the galactic plane very often in its life so has dispersed less than is the case in most clusters.  This makes it one of the oldest open clusters and it is believed to be about 5 thousand million years old.  It contains at least 130 stars from 12th to 17th magnitude but, being so old, it contains no blue stars, only yellow and red stars.  It is 5,000 light years away and subtends 15 arc minutes which corresponds to about 22 light years across.



Date and Time: 9th January 2011 00:23 to 00:39 UT
Camera: MX716
Telescope: ETX125 with 0.33 focal reducer*
Capture: Starlight Xpress. 11 frames, 60" exposure
Processing: star_mx7.  Dark-frame subtraction, enhancement factor 25, black level.
    Irfanview. Conversion to png format.
    RegiStax. 11 frames stacked, wavelets 1-2=5, histogram 7-255, gamma 1.2
    PhotoImpact. Vertical flip, reduction to 84%.


*This is my older reducer which was defective producing coma in the lower part of the image.


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