Saturday, May 1
May’s AAVSO variable of the month is the deep red star V Hydrae. Located in the constellation Hydra the Water Snake, you’ll find it by looking south after sunset. First, find Nu (ν) Hydrae, which glows at magnitude 3 and sits near magnitude 4 Alkes (Alpha [α] Crateris) in neighboring Crater. Then, using binoculars, slide 5° south of Nu to spot 7th-magnitude V Hydrae. V Hya gains its deep red color from its age: It is a type of cool red giant known as a carbon star for the vast quantities of carbon “soot” in its atmosphere. Carbon preferentially scatters blue light but lets red light pass by unhindered, which is why such stars appear so strikingly red.
In 1888, S.C. Chandler of Harvard University discovered that V Hya varies in brightness with a period of about 530 days. Over that time, its light changes by roughly a factor of 11. The star also has a longer period — 18 years — over which its appearance changes even more. Astronomers think the short period is due to stellar pulsations, while dimming over the long term is more likely attributed to a disk of obscuring material around the aging sun.
Sunrise: 6:00 A.M.
Sunset: 7:55 P.M.
Moonrise: 12:33 A.M.
Moonset: 9:45 A.M.
Moon Phase: Waning gibbous (73%)
Sunday, May 2
Asteroids 4 Vesta and 29 Amphitrite share the constellation Leo in May. Vesta is located near the Lion’s hindquarters, starting the month out about 14° southeast of 51 Leonis. Over the next several weeks, the 300-mile-wide (480 kilometers), magnitude 7.5 space rock will slide several degrees toward the famous Leo Triplet of galaxies: M65, M66, and NGC 3628.
Over near Leo’s heart — bright Regulus, also called Cor Leonis — is Amphitrite. It’s currently a little less than 2° to the star’s northwest and will draw closer to the luminary over the next two weeks. Be sure to check back on May 13th, when it will appear to skim close to the star, nearly (but not quite) blocking it out.
Both asteroids are moving relatively slowly and you’ll need to observe them for two to three nights to really notice their motion. They’ll be easily visible most of the month, only blotted out by the Moon’s bright light from May 18 to 21.
Sunrise: 5:58 A.M.
Sunset: 7:56 P.M.
Moonrise: 1:32 A.M.
Moonset: 10:50 A.M.
Moon Phase: Waning gibbous (62%)
Monday, May 3
A nearly Last Quarter Moon rises shortly after 2 A.M. local time in Capricornus the Sea Goat. Nearby is magnitude 0.4 Saturn, which is still bright enough to pop out against the background light. Saturn sits less than 1° from much fainter magnitude 4 Theta (θ) Capricorni and directly above magnitude 3.8 Zeta (ζ) Capricorni, once the latter rises.
Zoom in on the scene with a telescope to enjoy Saturn’s 17″-wide disk. The planet’s stunning rings span 40″ across their long axis and 11″ across the short axis. This morning, you’ll find Saturn’s largest moon, Titan, 2.8′ due east of the planet. The moon — the brightest of Saturn’s gaggle — is a relatively easy magnitude 8.4. Several other, fainter moons crowd around the rings: 10th-magnitude Tethys, Dione, and Rhea, as well as 12th-magnitude Enceladus. See how many of the small worlds you can spot with our own bright Moon nearby; come back a few days later, once the Moon has moved on, for a better view.
The Moon passes 4° south of Saturn at 1 P.M. EDT and Last Quarter Moon occurs at 3:50 P.M. EDT.
Sunrise: 5:57 A.M.
Sunset: 7:57 P.M.
Moonrise: 2:18 A.M.
Moonset: 11:58 A.M.
Moon Phase: Waning gibbous (51%)
Tuesday, May 4
The waning crescent Moon rises early this morning again in Capricornus, just to the lower right (southwest) of Jupiter, which currently lies in Aquarius. Deneb Algedi sits between them. By sunrise, our satellite is about 8.5° from the planet; the Moon will later pass 5° due south of Jupiter at 5 P.M. EDT.
While you’re out enjoying the early-morning sky, look northeast of Jupiter to spot the Great Square of Pegasus. This large asterism is bounded by four stars: Markab, Scheat, Alpheratz, and Algenib. Challenge yourself before the sky grows too light by searching out M15, a bright (magnitude 6.2) globular cluster that sits west of the Great Square and about 4° northwest of Enif, the brightest star in the Winged Horse, which marks his nose.
Discovered in 1746, M15 spans roughly 18′, which corresponds to a size of about 175 light-years at its distance of 33,000 light-years. Although it appears just at the edge of naked-eye visibility, in reality its numerous stars glow with a combined brightness 360,000 times that of our Sun.
Sunrise: 5:56 A.M.
Sunset: 7:58 P.M.
Moonrise: 2:57 A.M.
Moonset: 1:05 P.M.
Moon Phase: Waning crescent (41%)
Wednesday, May 5
The Eta Aquariid meteor shower peaks tonight, but the best time to catch the most shower meteors is actually early tomorrow morning (May 6).
Since you’ll want to be up before the Sun tomorrow, get all your observing in today early in the evening. Thirty minutes after sunset, Venus is 3° above the western horizon. That’s low, but its bright glow — magnitude –3.9 — makes it easier to spot. Mercury is a dimmer magnitude –0.8, but it’s also higher, sitting 7.5° above Venus.
Fifteen minutes later, Venus is setting but the stars of the Pleiades are starting to pop out in the darkening sky. The famous open cluster sits just over 3.5° west (to the lower right) of Mercury. Also visible now is bright red Aldebaran, the eye of Taurus the Bull, as well as the Bull’s two horn tips, Elnath and Alheka. Look above them in the sky and you’ll spot Mars, still shining at magnitude 1.3 near the feet of Gemini the Twins.
Sunrise: 5:55 A.M.
Sunset: 7:59 P.M.
Moonrise: 3:28 A.M.
Moonset: 4:09 P.M.
Moon Phase: Waning crescent (31%)
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