Here's the transcript to our latest constellation tour podcast. In this one, we take a tour of Cassiopeia the Queen.
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Hello, welcome to Astronomy magazine’s podcast. I’m Senior Editor Michael Bakich. In this week’s show, I’m taking you on a tour of the constellation Cassiopeia the Queen.
To the Greeks, Cassiopeia was the Queen of Ethiopia. She was King Cepheus’ wife and her daughter was Andromeda. Cassiopeia once boasted she and her daughter were more beautiful than the Nereids, who were immortal sea-nymphs. Their father, Nereus, complained to the sea-god Poseidon, who sent the sea-monster Cetus to terrorize the countryside.
The only sacrifice that could appease Cetus was Andromeda, so she was chained to a rock to await her doom. As luck would have it, the hero Perseus flew in and rescued her, and they lived happily ever after.
Five constellations border Cassiopeia: Andromeda the Princess, Camelopardalis the Giraffe, Cepheus the King, Lacerta the Lizard, and Perseus the Hero.
As for its size, Cassiopeia ranks as the 25th largest of the 88 constellations that cover the sky. It envelops 598 square degrees; that’s 1.45 percent of the sky.
While Cassiopeia falls toward the upper-middle of the size range, it ranks as the 30th-brightest constellation. It contains only four of the 200 brightest stars, but none of the top 50 most brilliant. Its brightest star is Schedar (Alpha Cassiopeiae), which shines at magnitude 2.24. In all, Cassiopeia contains 51 stars brighter than magnitude 5.5.
In addition to Schedar, many of Cassiopeia’s stars have unusual-sounding proper names. Among them are Achird, Caph, Cih (alternately spelled Tsih), Ksora, Navi, Ruchbah, and Segin.
The best single date to see Cassiopeia is October 9. The farther north you live, the more nights you’ll see Cassiopeia. Its visibility peaks in autumn, when it lies highest in the sky. In early October, its part of the sky lies opposite the Sun, and it’s visible the whole night. The worst time to look for Cassiopeia is around April 11.
Cassiopeia is a northern constellation. It’s completely visible north of latitude 12° south. You’ll see no part of the constellation if you live south of latitude 44° south.
Unfortunately, Cassiopeia has no meteor showers associated with it.
Cassiopeia contains two asterisms. The difference between an asterism and a constellations is that an asterism isn’t one of the 88 “official” constellations. Rather, it’s just a recognizable group of stars that forms some picture.
The constellation’s first asterism is the “W,” which includes five of the constellation’s bright stars. To form the W, start with Epsilon (ε) Cassiopeiae, then head to Delta (δ), Gamma (γ), Alpha (α), and Beta (β) Cas. But it’s only a W about half the night. The other half, it’s just as fair to call it the “M.”
The Queen’s second asterism is the Three Guides, but only one of the three stars — Beta Cassiopeiae — lies in the constellation. The other two stars are Alpha Andromedae and Gamma Pegasi. Now, here’s some trivia for you celestial navigators: Together, these three stars mark the equinoctial colure, the great circle that intersects both poles and both equinoxes.
Because parts of this constellation lie in or near the Milky Way, Cassiopeia is loaded with deep-sky objects. Two of them are Messier objects: M52 (pictured at left), and M103. Both of these objects are open star clusters.
Use Alpha and Beta Cas to help you find M52. Draw a line from Alpha through Beta, and extend the line just a bit farther than the separation between those two bright stars. This spectacular cluster shines at magnitude 6.9, so you won’t spot it without optical aid.
Through a medium-size telescope, you’ll see 75 stars ranging from 9th to 12th magnitude. Look for a prominent clump of six stars on M52’s eastern edge. The western edge also is well-defined against the starry background.
Cassiopeia’s other Messier object — M103 — lies only 1° east-northeast of magnitude 2.7 Delta Cas. This magnitude 7.4 cluster may not look spectacular, but its 40 bright stars stand out well from the rich fields of the Milky Way. Member stars range from 8th through 13th magnitude and group tightly in a triangle 5' across.
As you tour Cassiopeia, don’t miss the Owl Cluster, also known as NGC 457. It lies 2.1° southwest of Delta Cas. NGC 457 contains 25 stars brighter than 12th magnitude. Its most luminous star shines at magnitude 8.6 A 6-inch telescope at 50x shows nearly 75 cluster stars. As you observe the Owl Cluster, note the uniform background glow from distant, unresolved Milky Way stars.
While observing this open cluster in 1977, current Astronomy Editor David Eicher saw an owl figure made of the two brightest stars and the overall shape. He’s the one who dubbed this group the Owl Cluster.
The emission nebula called the Pac Man Nebula (NGC 281) sits less than 2° east of Alpha Cas. Photographs show the nebula’s classic shape, which led to its now dated nickname. It measures 0.5° across and has a dark lane that divides the brighter from the dimmer part. A nebula filter really will help you get the most out of the view. An 8th-magnitude star that forms the Pac Man’s eye shines through the brightest part of the nebula. This young, hot star provides most of the energy that causes NGC 281 to glow.
Now for an object you won’t spot through your backyard telescope. B Cas (pictured at right), also known as “Tycho’s Star,” represents the supernova of 1572, one of only four observed supernova that originated in our galaxy. The others are the supernova of 1006 in Lupus, 1054 in Taurus (that’s the event that produced the Crab Nebula), and 1604 in Ophiuchus, now known as “Kepler’s Star.” Tycho’s Star was visible to the unaided eye for more than 16 months, and, at its brightest, observers could spot this object in full daylight.
And with that, I’ll wrap up our look at Cassiopeia. If you want to see a chart of this constellation, you can find it on this episode’s page at Astronomy.com/podcast.
If you have any questions or comments about this episode, you can contact us at podcast@astronomy.com.
Until then, thanks for listening.
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