Sunday, August 21
The constellation Serpens is the only such star pattern that is broken into two distinct pieces: Serpens Cauda (the Serpent’s Tail) and Serpens Caput (the Serpent’s Head). The reason for this strange setup is that Ophiuchus the Serpent-bearer is carrying this celestial snake through the sky, and his territory breaks up the area dedicated to his load.
Tonight, we’ll concentrate on the front portion of the snake: Serpens Caput. It’s located in the southwestern sky after sunset and fortunately isn’t hard to find. Most observers use two bright red giant stars — Antares in Scorpius and Arcturus in Boötes — to guide them in their hunt. Once you’ve found these two stars, draw an imaginary line between them and look about halfway along it. Then tilt your gaze just north of that point, and you’re in Serpens Caput.
Magnitude 2.6 Unukalhai is this constellation’s brightest star, which lies in roughly the center of this constellation. Some 15 times as wide as our Sun, this star is no longer in the hydrogen-burning phase of its life, but has begun fusing heavier elements like carbon and oxygen instead. About 10° to this star’s north is a triangle of three stars that you can likely visualize as a snake’s head, outlined by Beta, Gamma, and Kappa (κ) Serpentis.
Sunrise: 6:17 A.M.
Sunset: 7:48 P.M.
Moonrise: 12:45 A.M.
Moonset: 4:32 P.M.
Moon Phase: Waning crescent (27%)
Monday, August 22
Asteroid 4 Vesta reaches opposition at 3 P.M. EDT. This large, bright, main-belt world is visible all night in Aquarius, floating near another famous planetary nebula: NGC 7293, also called the Helix Nebula. For the best viewing, wait at least two hours after sunset for the sky to get nice and dark and for the region housing Vesta and the Helix nebula to climb out of the haze near the horizon in the southeastern sky.
First, let’s find Vesta. At magnitude 5.8, it’s just at the edge of naked-eye visibility from a good, dark observing site. Otherwise, binoculars or any small scope will certainly capture it. Our quarry sits 9.5° west-southwest of magnitude 3.3 Skat in Aquarius. Alternatively, you can drop 8.5° southeast of magnitude 2.9 Deneb Algedi in Capricornus, or 11.5° southeast of Saturn, which tonight shines at magnitude 0.3.
Now, let’s try something harder: the Helix. Astronomy contributing editor Michael E. Bakich has called this planetary nebula “one of the brightest hard-to-see objects in the sky.” That’s because despite its magnitude of 7.3, the Helix stretches 13′ across, smearing that light out across a large area and rendering its surface brightness low. Bakich says you can find it in binoculars with lenses larger than 50 millimeters that give 7x to 15x magnification. However, he recommends at least a 4-inch scope or larger for a brighter, more detailed view. Stick to low magnifications to see the whole nebula or bump up the power to examine just a portion of it.
Tonight, the Helix sits just 2.5° east-southeast of Vesta. If you need a brighter signpost, look 7.8° southwest of Skat or 1.2° due west of 5th-magnitude Upsilon (Ï…) Aquarii.
Sunrise: 6:18 A.M.
Sunset: 7:47 P.M.
Moonrise: 1:31 A.M.
Moonset: 5:24 P.M.
Moon Phase: Waning crescent (19%)
The Sky This Week: Vesta visits the Helix
Source: Trending Update Article
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