Here is the transcript for my podcast about how to see the Zubeneschamali, globular cluster M5, and elliptical galaxy NGC 4697 this week.
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Each week, I highlight three different night-sky targets for you to see:
- One object you can find with your naked eyes or through binoculars
- One object to find with a small telescope
- One deep-sky object to find with an 8-inch or larger telescope for you avid astronomers
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A stellar tongue-twister
This week’s naked-eye object is the brightest star in the constellation Libra the Scales. It’s Zubeneschamali, also known as Beta (β) Librae. The star’s name comes from the Arabic for “the northern claw.”
That was long ago, when Libra didn’t exist. Instead, its brightest stars represented the claws of the constellation just to its east — Scorpius the Scorpion. Zubeneschamali was the northern claw, and Zubenelgenubi was the southern claw. You’ll find Zubenelgenubi about 9° southwest of Zubeneschamali.
Libra is a case where the normal Alpha, Beta, Gamma, etc., rule for denoting a constellation’s brightest stars — in order — breaks down. An early celestial mapmaker rated Zubeneschamali as Libra’s second-brightest star. We know today, however, that it’s actually the brightest. It shines at magnitude 2.6, while Alpha (α) Librae’s magnitude is 2.75, about 15 percent fainter.
Ok, you’ve now found two stars with funny names. But there’s more. Go out some night, and locate Zubeneschamali. Don’t use a telescope or even binoculars. Just look at it with your eyes. What color does it appear to you?
Since the mid-1970s, I’ve had an ongoing debate with some of my closest observing friends about the color of this star. I see it as green, and so have many others I’ve asked. But some amateur astronomers whose opinions I value and who I agree with about the majority of star colors think I’m crazy. Their take on Zubeneschamali is that it’s either white or light-blue.
So please help me settle this debate. Cast your gaze on Zubeneschamali, and decide for yourself if it is indeed the only naked-eye star with a greenish tint. Then, e-mail me at mbakich@astronomy.com with your conclusion. I’ll discuss the results in an upcoming blog.
Small-scope standout
This week’s small telescope target is globular cluster M5 in the constellation Serpens — the brightest globular cluster in the northern half of the sky. You can find it by starting at Zubeneschamali. From that star, move 11.5° due north. If you have sharp eyes, and if your observing site is dark enough, you can spot M5 as a fuzzy magnitude 5.7 star without optical aid. Don’t confuse it with 5 Serpentis, a magnitude 5.0 star 22' to the southeast.
Through a 4-inch telescope, this cluster is full of detail. When you crank up the magnification to 150x or more, you’ll see that M5 has a grainy structure. You’ll spot several dozen stars around the core, which accounts for about one-quarter of the cluster’s diameter. Through an 11-inch scope, more than a hundred stars pop into view. Streamers of stars fill M5’s outer regions. They provide a nice contrast to the relatively sparse background.
Caldwell that ends well
This week’s deep-sky object is elliptical galaxy NGC 4697 in the constellation Virgo. It’s also known as Caldwell 52, which most writers abbreviate as C52. This object is one of 109 deep-sky treats on a list compiled by British amateur astronomer and popularizer Sir Alfred Patrick Caldwell-Moore. At magnitude 9.2, it ranks as one of the sky’s brightest galaxies.
You’ll find this galaxy 5.3° west of magnitude 4.4 Theta (θ) Virginis. A small telescope will reveal its hazy nature and oblong shape.
Step up to an 11-inch scope, and you’ll see much more detail. Regions of this galaxy outside the core show a threefold variance in brightness, getting fainter as you move away from the core.
The bright central region’s shape may remind you of a spiral galaxy. In fact, astronomers categorize NGC 4697 as a lenticular galaxy — one with characteristics of an elliptical but with a toehold on the first rung of a spiral galaxy’s evolutionary ladder.
If you’re using a 16-inch or larger telescope, you might notice an ultra-faint object 6' west-northwest of NGC 4697. That’s PGC 170203. This spiral galaxy has a dismal magnitude of 15.1, so I’ll forgive you if you don’t spend much time observing it.
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Previous episode: The Kite, globular cluster M53, and the Hockey Stick Galaxy