The Sky This Week from May 15 to 22 – Astronomy Magazine

Saturday, May 16The Moon passes 4 south of Neptune at 11 A.M. EDT. Two hours before sunrise, the pair are 6.5 apart and low on the eastern horizon shortly after rising. Follow them upward as the sky lightens with dawn. The Moon is just 33 percent lit and waning, while Neptune glows at magnitude 6, its disk appearing just 2" across. The nearest bright star is magnitude 4.2 Phi () Aquarii, a red-hued star that offers a glimpse of our Suns future. Currently in the red giant phase of its life, Phi is more than 260 times as luminous as the Sun and almost 39 times as wide. The star will eventually run out of nuclear fuel and its core will turn into a tiny white dwarf, lighting up what once was the stars own atmosphere as a beautiful planetary nebula.

Sunday, May 17Mercury passes 7 north of Aldebaran at 5 A.M. EDT. Because the pair trails the Sun in the sky, they wont be visible until sunset. About 20 minutes after sunset, the sky will still be bright. At that time, Mercury will hover just 9 high, with Aldebaran a mere 3 above the horizon. The two are now nearly 8 apart. Venus is roughly 9 northeast of Mercury, both brighter and higher in the sky, making it easier to spot. The two planets are drawing closer and will pass within 0.9 of each other in just a few days.

Monday, May 18The Moon reaches apogee at 3:45 A.M. EDT, when it will be 252,018 miles (405,584 km) from Earth. Rising just after 4 A.M. local time, our satellite is a smidge less than 17 percent lit and waning fast. Look for a mere sliver of a crescent in the southeast before sunrise, hanging against the brightening backdrop.

Above it in the sky is the Square of Pegasus, outlined by Alpheratz, Scheat, Markab, and Algenib. A little less than 20.5 west of Markab is the supergiant star Enif (Epsilon [] Pegasi), which represents the nose or muzzle of the flying horses figure. Coming in at roughly 150 times the diameter of our Sun, if placed in the center of our solar system, Enif would reach halfway to Venus. To the south of Enif are Alpha () and Beta () Aquarii, which are roughly as bright as Enif. The three also sit at roughly the same distance from Earth. Astronomers think the trio may have been born in the same group of stars, slowly drifting apart over the past 15 million years.

Tuesday, May 19Jupiter and Saturn rise in the southeast not long after local midnight, climbing higher in the sky as the morning hours tick by. The gas giants stand about 4.7 apart, glowing at magnitudes 2.5 and 0.5, respectively.

Once youve found the planets, draw an imaginary line between them. Halfway along that line, glance just over 1 due south to find M75 (NGC 6864), a tightly packed globular cluster considered to have the densest core of all Messiers globulars. This cluster is so dense, in fact, that it still appears starlike in binoculars, and apertures of 10 inches or larger are required to truly begin resolving the clusters stars. The 13-billion-year-old sphere of stars contains about 400,000 members and sits roughly 67,500 light-years from Earth.

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The Sky This Week from May 15 to 22 - Astronomy Magazine