Tuesday, June 16
Uranus stands about 10° high in the east at 4:30 A.M. local time. The magnitude 5.9 planet has a disk just 3" across and hangs 10° left of the Moon. This morning, our satellite is a beautiful 22-percent-lit crescent in the northeastern portion of the constellation Pisces. Nearby bright stars include magnitude 2 Hamal in Aries and magnitude 2.5 Menkar in Cetus. Uranus appears roughly halfway on a line between these two bright stars. Farther east is the famous Pleiades, whose dipper shape should still be relatively easy to find in the brightening sky. Later tonight, the Moon will pass 4° south of Uranus at 10 P.M. EDT.
For those who prefer evening observing, Comet PanSTARRS (C/2017 T2) is less than 1° from the barred spiral galaxy M109 (NGC 3992) tonight. Located in Ursa Major near the cup of the Big Dipper, both are visible all night from the northern U.S. All observers will want to catch the pair earlier rather than later, however, when the Great Bear is higher in the sky. The comet and its extragalactic companion are near Phecda (Gamma [γ] Ursae Majoris), the star that marks the lower left corner of the Dipper’s cup. Look 40" east of the star to find M109, then about 40" southwest of the galaxy to find the roughly magnitude 9 comet.
Wednesday, June 17
Mercury is stationary at 4 P.M. EDT. The tiny planet is 10° high around sunset and disappears below the horizon within an hour.
Whether you’re able to spot Mercury or not, you might see something else: noctilucent, or “night-glowing,” clouds. Common during warmer seasons, these clouds occur when ice crystals form on high-altitude dust particles 40 to 50 miles (64 to 80 km) above the ground. These pearly white clouds appear to glow even as other, lower clouds — which form more than 10 times lower — darken as night falls. These clouds are not unique to Earth, either — the Mars Curiosity rover has imaged
noctilucent clouds drifting through the Red Planet’s skies.
Thursday, June 18
Venus now appears in the morning sky after its June 3 inferior conjunction. This morning, the magnitude –4.3 planet is 4° high 45 minutes before sunrise. It hangs 11° east of a 27-day-old crescent Moon. Through binoculars or a telescope, you’ll be able to see that its 52"-wide disk is a mere 7 percent lit. Tomorrow morning, the Moon will pass in front of, or occult, Venus from some parts of the world. Whether you can view the event or not, you will find the Moon much closer to our sister planet, so make sure to come back in 24 hours to see how the scene has changed.
Less than 10° above the planet in the sky is the sparkling Pleiades. Due north of this open cluster is the constellation Perseus the Hero. His beta star is magnitude 2.1 Algol. Sometimes called “the demon star,” Algol represents the gorgon Medusa’s severed head, held by Perseus, in depictions of the constellation’s figure. The star is actually an eclipsing binary system, tilted edge-on with respect to Earth. Every 2.867 days, the main star’s smaller, dimmer companion passes in front of it, causing Algol to appear to drop to magnitude 3.4 — just 30 percent its original brightness. The star appears to recover its glow within hours.