Globular Cluster M3 (NGC 5272), class VI, in Canes Venatici

Right Ascension 13 : 42.2 (h:m); Declination +28 : 23 (deg:m); Distance 33.900 light years;
Visual Brightness 6.2 (mag); Apparent Dimension 16.2 (arc min)

M3 is one of the most outstanding globular clusters, containing an estimated half million stars. At a distance of about 33,900 light years, it is further away than the center of our Galaxy, the Milky Way, but still shines at magnitude 6.2, as its absolute magnitude is about -8.93, corresponding to a luminosity of about 300,000 times that of our sun. M3 is thus visible to the naked eye under very good conditions - and a superb object with the slightest optical aid. Its apparent diameter of 16.2 arc minutes corresponds to a linear extension of about 160 light years.

Source and more: SEDS

April 1, 2007 20:01 - 20:51 UT.
Imaging: William Optics Zenithstar 80 ED II APO, f/6.8 [focal length 545 mm] with 5 cm extender, Astronomik LRGB filters; ATK16IC b/w camera, K3CCDTools.
Exposures: Luminosity 19x90 seconds; RGB 10x30 seconds; autoguided.

April 14, 2004 22:02 - 22:15 UT.
Imaging: TAL-2M 150mm f/8 in Prime Focus, Vesta Pro-SC3a b/w RAW, Baader Infra Red blocking filter, 14 x 9 secs exposure

March 27, 2003 23:47 - 00:05 UT
Observe the nice blue colours of several stars.
Prime Focus, 11 x 20 seconds exposure.
YRGB processing.