Springtime Cluster #1: The Beehive (M44)

At last! A clear night in what so far has been an awful spring. The long-awaited arrival of mild spring nights brings a sky sprinkled with a few naked-eye star clusters. This is the most famous, and appears as a fuzzy glow in the constellation of Cancer the Crab. Indeed, to the unaided eye, there’s not much else to see in Cancer. But this cluster is a dandy in binoculars. Called the Beehive, this is one of the few deep-sky objects known since antiquity. Apparently, the Greek poet Aratos mentioned it in 260 B.C., describing it as a “little mist.” A hundred years later Hipparchus included it in his star catalog, calling it a “cloudy star.”

It wasn’t until 1609 that Galileo, using his pioneering telescope, resolved the cloud into a mass of stars. Any binoculars will do the same today. This close-up view more closely matches the view through a modern telescope, showing its subtly coloured blue and yellow stars.

In 1769 Charles Messier included it as object #44 (the Pleiades was #45) in his first catalog of what we now call deep-sky wonders. To him, however, these fuzzy spots in the sky were just distractions to his goal of hunting the fuzzy things that really mattered – comets.

The stars of M44 really do belong together in a gravitationally-bound cluster of up to 1000 stars, traveling together through space since the time about 600 million years ago when they formed out of what must have been a massive gas cloud. That’s a pretty good age for a star cluster; most break apart and scatter around the Galaxy after just a few tens of millions of years. However, the Beehive sits about 600 light years away, above the main disk of the Milky Way and its spiral arms. Its location makes it partly immune to the disruptive tidal forces of the Galaxy. Because it lies above the galactic plane we see it far off the band of the Milky Way, shining in our spring sky sparsely populated with bright stars and lacking the rich assortment of clusters and nebulas scattered along the winter and summer Milky Way.

For this exposure I used a favourite scope, the TMB 92mm apo refractor, a compact and fast little telescope perfect for imaging big binocular-class objects like this. This is a stack of four 4-minute exposures at ISO 800 with the Canon 7D camera. A Photoshop routine added the diffraction spikes, purely for photogenic value.

– Alan Dyer, April 2011 / Image © 2011 Alan Dyer

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