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Here is the transcript for my podcast about how to see the star V Hydrae, globular cluster NGC 5634, and the Ursa Minor Dwarf this week.
Check out the Astronomy.com's interactive star chart — StarDome — to see an accurate map of your sky. It'll help you locate some of this week's key targets. Astronomy magazine subscribers have access to a slew of cool functions with StarDome PLUS.
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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As red as it gets
Our first target is the star V Hydrae. To find it, use binoculars, and look toward the center of the huge constellation Hydra. V Hydrae lies near that star pattern’s border with the constellation Crater.
Locate the 4th-magnitude star Alkes (Alpha [α] Crateris). Sweep your binoculars 3.5° (that’s about half the field of view of 7x50 binoculars) toward the south-southwest. Or, just center Alkes and look to about the 5 o’clock position at the edge of the field of view. V Hydrae should be sitting there.
The special thing about V Hydrae is its color. Of all the stars I’ve seen — and I’ve seen a lot — this one’s the reddest. Think ruby, crimson, or blood, and then deepen it a shade. I’m talking red.
Astronomers classify V Hydrae as a type of variable star known as a carbon star. A huge amount of carbon soot accumulates in the upper atmosphere of such stars. The carbon is black, not red, but the particles scatter short-wavelength light, which are the colors near the blue end of the spectrum. What’s left for us to view is the red component of the star’s light.
As the particles build up, the star fades in brightness and also gets redder. Eventually, the carbon absorbs enough radiation to escape the star, and the cycle starts again.
V Hydrae takes 531 days to complete one cycle. During that time, its magnitude drops from 6.6 to 9.0 and rises back again. That means at minimum, the star shines only 11 percent as bright as when it’s at maximum.
A globular among the galaxies
Our next target is globular cluster NGC 5634 in Virgo. It lies halfway between magnitude 3.9 Mu (μ) Virginis and magnitude 4.1 Syrma (Iota (ι) Virginis).
Let’s be honest. The constellation Virgo is known for its galaxies. It contains some 200 deep-sky objects brighter than 13th magnitude. Only one — NGC 5634 — is a globular cluster.
Point a 4-inch telescope at this object, and you’ll see lots of faint stars and one bright orange one — magnitude 8.0 SAO 139967, which sits a bit more than 1' east-southeast of the cluster’s center. The star isn’t part of NGC 5634. It just happens to lie in the same direction from our viewpoint.
The cluster’s stars are condensed, meaning you won’t easily resolve them into individual points. But the back-and-forth visibility battle you’ll encounter between the star and the cluster makes for a fascinating observation.
That’s dwarf, not midget
Our next object lies in the southernmost part of the northernmost constellation. The Ursa Minor Dwarf is a dwarf elliptical galaxy whose name comes from its home constellation, Ursa Minor.
I suggest you use at least an 11-inch telescope, but don’t crank the power up. In fact, you’ll want to use the lowest-magnification, widest-field eyepiece you own.
That’s because this galaxy covers one and a half times more area than the Full Moon. It measures 41' by 26'.
It has a respectable magnitude, 10.9, but because that light is so spread out, the Ursa Minor Dwarf has a miserably low surface brightness.
The best approach for viewing this object is to head to the darkest observing site you can get to. Then, disengage your telescope’s drive, and slowly sweep the Dwarf’s region of sky. What you’re looking for is an ever-so-slight increase in the background glow of your eyepiece’s field of view. Good luck.
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Previous podcast: Partial constellation Serpens Caput, M40, and lenticular galaxy M85