Astro Bob: Cassiopeia spells 'W' in June
Sitting almost directly below the Pole Star this month, Cassiopeia really does look like a W. We explore its wonders.
DULUTH — You'll often hear Cassiopeia described as having a W shape. This is only sometimes true. In fall it's tipped up on one side and looks like a stellar zigzag. During winter, when the constellation stands highest in the sky, it practically shouts "M!" With the return of spring, the group demonstrates its Greek language skills by inscribing the capital letter sigma in the firmament.
So when is it a W? Right now as it turns out. In June, Cassiopeia sits flat in the northern sky just after reaching its lowest point called nadir. In this position there's no mistaking it for anything else but a wonderful, whimsical W.
Here in Duluth, Minnesota, the W stands about 20° (two fists) high at nightfall, but the farther south you live the closer it gets to the horizon. In Des Moines, Cassiopeia's about 15° high, but only 8° from Atlanta. Tucsonans see it scrape along the horizon, while farther south in Miami all but the center star in the W are hidden by the northern horizon.
Aurora seekers can always count on a lot of Cassiopeia-time during the late spring and early summer as we face north with hopeful hearts. It's so easy to get used to seeing "the W" we sometimes forget we're looking at an asterism — a convenient pattern of bright stars — and not the complete constellation. Once the adjacent stars are connected in, Cassiopeia transforms into a queen sitting in a chair checking her face in a mirror. By the way, the queen should be wearing a seat belt lest she fall out of her chair. Not till fall will she sit upright again.
You may want to consider leaving your seat the next clear night for a look at Cassiopeia. The Milky Way band unfurls across the constellation, making it one of the richest areas in the sky for star clusters. Of the more than 1,100 known open clusters (loose gaggles of stars like the Pleiades) in our galaxy about 106 reside in Cassiopeia.
Two of them — M103 and the ET Cluster (NGC 457), along with the Double Cluster in neighboring Perseus — are easy to spot in a pair of binoculars. They look kind of fuzzy at first. But if you focus sharply and beam in you'll see they're peppered with tiny stars. The ET Cluster gets it name from the character E.T. in the movie "E.T. the Extra-Terrestrial" because the group's two bright "eyes" and gangly shape reminded them of the beloved alien. It's also known as the Owl Cluster and lies over 7,900 light-years away.
All four clusters look much more impressive in a small telescope, but at least binoculars will give you a taste. I use 10x50s — that's a magnification of 10x and a lens diameter of 50-mm or about 2 inches. For many night-sky aficionados these (or the similar 7x50s) are ideal for astronomy because they combine modest magnification with good light-gathering power.
Now that you know the ABCs of the W, be a witness to its wonder the next clear night. Clear skies!