Archive for November 21st, 2009

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Mission 11: Cassiopeia and the Double Cluster

November 21, 2009

Mission Objectives: Constellation, Open Cluster, Bright Star

Equipment: Naked eye, Binoculars, Telescope

Required Time: 3 minutes

Instructions: Go outside after dark, face northeast, and look for the sideways W. If you’re not sure which W is which, take a free sky map. The W is Cassiopeia, which lies right smack in the middle of the winter Milky Way.

Cassiopeia is a deep sky wonderland in binoculars and telescopes. There are more star clusters than you can shake a stick at–a decent portable sky atlas will show a dozen or more. Even without an atlas, it’s an awesome area to scan around in with optics of any size.

I have a confession, though. Almost every time I go out to observe in the winter, I give Cassiopeia a quick once-over and then leave. Why? Because there’s an even better pair of clusters lurking over the border of the neighboring constellation, Perseus, and Cassiopeia is such a good pointer that you might think it was put there for that purpose. Follow the inner leg of the shallow half of the W about 2/3 of the way to the next bright star, and you’ll find the Double Cluster, NGC 869 and 884. Keep in mind the effect of sky rotation–by 8:30 PM, Cassiopeia is an M centered over the North Star, and by midnight it’s a sigma to the northwest. Adjust your expectations accordingly.

The Double Cluster is one of the finest objects in the night sky, and almost always makes it onto lists with names like “Top 10 Telescopic Targets”. I’m not going to show you any pictures of the clusters themselves, because this is one place where pictures simply don’t do justice. You’ll have to get out under the night sky and see for yourself.

Once you’ve had your mind blown by the Double Cluster, keep on cruising in the same direction and follow the chain of bright stars to Mirphak, or Alpha Persei, the brightest star in the constellation Perseus. Mirphak is surrounded by a broad field of stars called the Alpha Persei association; it is too big to fit in the field of view of most telescopes (except possibly fast focal ratio, widefield scopes like the Astroscan and StarBlast 4.5), but is instead one of the best binocular targets in the entire sky. Have a look and let me know what you think.