NGC 457 (the “ET Cluster”)
December 2010 :
Have you seen “ET” lately? Not that cute little alien in Steven Spielberg’s 1982 movie. I’m referring to the ET-mimicking open star cluster NGC 457 in Cassiopeia. Discovered by William Herschel in 1787, NGC 457 is often overlooked because of its proximity to the Messier cluster M103. That’s an unfortunate situation. Not only is NGC 457 superior to M103 in visual appearance, it may well be the most spectacular of Cassiopeia’s clusters. As such, it’s a must-see for late-autumn star parties.
And it does bear a striking resemblance to Spielberg’s ET. Two bright stars, phi1 and phi2 (φ1 and φ2) Cassiopeiae, are ET’s eyes. A group of some 40 stars northwest of the “eyes” form ET’s body. Passing through the body is a row of stars that extends outward to the sides, creating the alien’s arms. Add a handful of stars to the base of the body, and ET has feet. Because phi1 is brighter than phi2, ET seems to be winking at us.
ET will greet the owner of even the most modest telescope. A standard 2.4-inch refractor can capture a few dozen cluster members, while an 8-inch reflector will snare one hundred. A magnification of just 50-75X comfortably encompasses the cluster’s 20 arc-minute width.
To find the NGC 457, trace a line from epsilon (ε) to delta (δ) Cassiopeiae, then extend it about two degrees beyond. Although the cluster’s published magnitude is 6.4, the presence within the cluster of 5th magnitude psi1 betrays the presence of NGC 457 to the unaided eye.
Is phi1 Cas a true member of NGC 457? Various distance measurements would indicate otherwise. While phi1 appears to be around 2000 light years away, studies place the main cluster at a distance of nearly 10,000 light years. However the distance estimates of NGC 457 are sketchy at best and one set of measures puts phi1 squarely within the bounds of the cluster. But let’s not quibble about statistics. Instead, train your telescope on NGC 457 and say hello to ET.
Your comments on this column are welcome. E-mail me at gchaple@hotmail.com
