Globular Cluster Messier 3
Along with Messier 13 in the constellation Hercules, Messier 3 is the most magnificent globular cluster in the northern starry sky. It was discovered by Charles Messier on 3rd May 1764. He described it as a round nebula without a star, becoming darker towards the outside.
What is remarkable about M 3 is its oval shape. The greatest star concentration is a little southwest of the center of the cluster. Similar to other large globular clusters, some outer stars seem to be arranged along a radial line, a phenomenon that was first noticed by the two Herschels and Lord Rosse. Rosse also found some dark areas in the central mass, similar to M 13. The presence of dark clouds is of great interest as it was generally assumed that globular clusters do not contain dust and gas. If one considers these dark nebulae as foreground objects, however, one could argue that such small dark nebulae could also be distributed all over the sky, but could not be detected due to the lack of a bright background object. However, M 3 lies in an area far away from the Milky Way, which is largely free of interstellar absorption. This suggests that the dark clouds actually belong to the globular cluster itself.
M 3 contains more than 45'000 stars from around 12 mag up to the limit of perceptibility. The number of variable stars is greater than in any other globular cluster observed. The period of most of these stars lasts about half a day, and in some cases the light changes so quickly that it doubles in ten minutes. Stars of this type, called cluster variables, appear to be a subclass of the known Cepheids. The typical example is the star RR Lyrae. Using the period-luminosity relationship, a distance of 31'000 light years could be determined. [4, 100]
|Right Ascension (J2000.0)||13h 42m 11.2s|
|Declination (J2000.0)||+28° 22' 34"|
|Visual magnitude||6.3 mag|
|Metric Distance||10.200 kpc|
|Dreyer Description||!!, globular cluster of stars, eB, vL, vsmbM, st 11…|
|Identification, Remarks||M 3, GCL 25|
The globular cluster is located between the constellations Bootes and Coma Berenices in the constellation Canes Venatici. It is roughly halfway from Arcturus (α Boötis) - Cor Caroli (α Canum Venaticorum), roughly where it is crossed by the connecting line ρ Bootis - β Comae Berenices. There the search for Messier 3 is to be started with a large field eyepiece. The globular cluster is highest in the sky from February to July.
400 mm Aperture: The sight of M 3 is a feast for the eyes, framed by a triangle of three stars. In the 21 mm ethos (85x), the globular cluster appears resolved right into the centre. With increasing magnification, more and more stars become visible in the core area until the cluster fills the entire image field. — 400 mm f/4.5 Taurus Dobsonian, Glaubenberg, SQM 21.34, a bit windy, Sahara dust and hazy, 22. 5. 2022, 00:15, Bernd Nies