M93, mag. +6.0, is a bright large open cluster of about 80 stars that's located in the southern constellation of Puppis. It has an apparent diameter of 22 arc minutes, corresponding to about 2/3rds that of the full Moon. Under dark skies, M93 is just about visible to the naked eye as a misty patch of light. It's an easy binocular object and a wonderful sight in small telescopes where the brightest stars are shaped like a triangle. The cluster was one of the last deep sky objects discovered by Charles Messier, which he catalogued on March 20, 1781.
Finding M93 is not difficult; it's positioned in western Puppis only a few degrees from the Canis Major border and not far from Sirius (α CMa) the brightest star in the night sky. Sirius shines at mag. -1.46 and can be easily found by connecting the three bright stars of Orion's belt and following the line southwards. Located 8 degrees southeast of Sirius are stars Omicron1 CMa (ο1 CMa - mag. +3.9) and Omicron2 CMa (ο2 CMa - mag. +3.0). Next imagine a line connecting these two stars and extend it eastwards, curving slightly southwards for about 10 degrees to arrive at M93.
A pair of 7x50 or 10x50 binoculars easily shows M93 and the triangular shape formed by the brightest stars. Through a small 80mm (3.1 inch) telescope at medium magnifications, M93 appears large and somewhat dense cluster. Towards the centre of the cluster is an arrowhead or wedge shaped grouping of bright stars. With averted vision, the nebulous background resolves into many fainter stars.
Larger telescopes of aperture 200mm (8-inch) or greater reveal dozens of members of mostly blue giants but some red giant stars that add to the charm of this already dazzling and beautiful cluster.
M93 has a spatial diameter of 20 light-years and is located 3600 light-years away. It's estimated to be about 100 million years old and is best seen from southern latitudes during the months of December, January and February.
M93 Data Table
|Object Type||Open Cluster|
|RA (J2000)||07h 44m 29s|
|DEC (J2000)||-23d 51m 11s|
|Apparent Size (arc mins)||22 x 22|
|Number of Stars||80|
|Other Name||Collinder 160|