Pluto’s peak appearance, a globular cluster in Ophiuchus, and other amazing things to look for in the sky this week.
By Richard Talcott
Wednesday, July 5
Despite the Moon’s presence, this week offers a good opportunity for binocular users to track down one of summer’s finest open star clusters. NGC 6231 lies in the tail of Scorpius the Scorpion, just 0.5° north of the double star Zeta (z) Scorpii (which is another fine binocular sight). NGC 6231 shines at magnitude 2.6 and packs more than 100 stars into a region about half the width of the Full Moon. This part of Scorpius lies nearly due south after darkness falls, though it doesn’t climb high from mid-northern latitudes.
Thursday, July 6
The waxing gibbous Moon passes just 3° north of Saturn this evening, helping point the way to the magnificent ringed planet. The two are on display nearly all night among the background stars of southern Ophiuchus, hanging in the southeastern sky as darkness falls and climbing high in the south by midnight local daylight time. The pair will look nice with the naked eye or binoculars, but telescope users will want to choose another night this week when the Moon isn’t so close to target the magnitude 0.1 planet. Saturn reached its peak just three weeks ago, when it appeared opposite the Sun in the sky, and our view of the ringed planet remains spectacular. A telescope reveals the world’s 18″-diameter disk surrounded by a dramatic ring system that spans 41″ and tilts 27° to our line of sight.
The Moon reaches apogee, the farthest point in its orbit around Earth, at 12:28 a.m. EDT. It then lies 252,236 miles (405,934 kilometers) from Earth’s center.
Friday, July 7
This week offers observers their first peek of Mercury during its current evening apparition. The innermost planet stands 6° high in the west-northwest a half-hour after sunset tonight. Although Mercury glows brightly, at magnitude –0.6, you might need binoculars to spot it initially against the twilight glow. A telescope reveals the planet’s disk, which spans 5.6″ and appears 80 percent lit.
Saturday, July 8
Full Moon officially arrives at 12:07 a.m. EDT tomorrow morning, but it looks completely illuminated all night. It appears low in the southeast as the Sun sets and climbs highest in the south around 1 a.m. local daylight time. The Full Moon resides among the background stars of Sagittarius the Archer throughout the night.
Sunday, July 9
Tonight marks the peak of Pluto’s 2017 appearance. The distant world reaches opposition, which means it lies opposite the Sun in our sky and remains visible all night. It glows dimly at 14th magnitude, however, so you’ll need an 8-inch or larger telescope with good optics to spot it visually. Pluto currently lies in northeastern Sagittarius, some 1.8° east-southeast of 3rd-magnitude Pi (p) Sagittarii. See “In pursuit of Pluto” in the July Astronomy for complete details on finding this world.