The Sky This Week for July 29 to July 24 2016
Saturn shines, Mercury and Venus have a close encounter, and the Delta Aquariads meteor shower flies by.
Wednesday, July 20
Look toward the south as darkness falls and you can’t help but see Mars. The Red Planet shines brilliantly at magnitude –1.0 — trailing only the Moon and Jupiter after dusk — against the much fainter background stars of Libra. And it remains visible until it dips below the southwestern horizon shortly after 1 a.m. local daylight time. When viewed through a telescope, Mars’ orange-red disk spans 14″ and shows a number of subtle dark markings. You also might glimpse the white north polar cap, which should be near its minimum extent now because summer ended in the planet’s northern hemisphere early this month.
Thursday, July 21
Pluto reached opposition and peak visibility two weeks ago, and it remains a tempting target all night. It glows dimly at magnitude 14.1, 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 0.6° west-southwest of the 3rd-magnitude star Pi (p) Sagittarii. See “The quest for distant Pluto” in the July Astronomy for complete details on finding this world.
Friday, July 22
Tonight 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 just 14′ in diameter. This part of Scorpius lies nearly due south after darkness falls, though it doesn’t climb high from mid-northern latitudes.
For observers across most of eastern North America, the waning gibbous Moon crosses directly in front of Neptune tonight. The 8th-magnitude planet will be difficult to see even through a telescope when it passes behind the Moon’s lit limb, but significantly easier when it reappears from behind the dark limb. Because exact times depend on your specific location, set up your scope in early evening to be ready for the show.
Saturday, July 23
The Southern Delta Aquarid meteor shower ramps up this week. The shower has a broad maximum in late July, but you should see a few members in the hours before dawn. Unfortunately, a waning gibbous Moon currently shares the morning sky, reducing the number of meteors you can see. To tell a Southern Delta Aquarid meteor from a random dust particle burning up in Earth’s atmosphere, trace the streak of light’s path backward. A shower meteor will appear to originate from the constellation Aquarius the Water-bearer.
Sunday, July 24
If you didn’t have a chance to view Neptune passing behind the Moon on Friday, try tracking down the distant planet tonight when it passes 31′ (the width of a Full Moon) due south of the 4th-magnitude star Lambda (l) Aquarii. The pair rises shortly after 10 p.m. local daylight time and climbs some 40° above the southern horizon by the start of morning twilight. You’ll need binoculars to spy magnitude 7.8 Neptune and a telescope to see its blue-gray disk, which spans 2.3″.
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