The sky this week from July 29 to August 5
Wednesday August 3
The slowly waxing Moon is in Virgo tonight, not far from the magnificent double star Porrima (Gamma [γ] Virginias). Thanks to a telescope, this luminous point is divided into two of roughly equal magnitude: 3.65 and 3.56. According Astronomy contributor Raymond Shubinski, “they look like two tiny beacons in space” about 3 inches apart.
But let’s get back to the Moon, where we’ll focus on a bit of strange terrain to the lunar east (west on the sky). Along the lower left (west) edge of the Sea of Tranquility are several north-south ripple ridges that really seem to stand out from the low angle of the sun. The nearly circular crater Arago has well-defined walls, while to the west lies half-buried Julius Caesar. Lunar researchers believe that over time, lava has erupted again and again in this region; one rim of Julius Caesar is lower than the other due to the sloping terrain where it formed, so only the upper portions of the crater rim remain readily visible. Just south of Julius Caesar is Rima Ariadaeus – a curious fissure that formed when the lunar surface split here.
Sunrise: 6:00 AM
Sunset: 8:11 p.m.
Moon setting: 11:20 p.m.
Moon phase: Wax Crescent (32%)
Thursday August 4
Mercury passes 0.7° north of Regulus in Leo at 1:00 a.m. EDT. The pair is visible shortly after sunset, still 0.1° farther away as it sinks towards the western horizon. Mercury is now magnitude -0.5 and is 4° high 30 minutes after sunset. You will need binoculars to find weaker Regulus (magnitude 1.4).
As Leo’s front half disappears into the growing darkness, turn your attention east to the big cat’s rear end. Three stars form a right-angled triangle here: 3rd magnitude Chertan and Zosma (5° north of Chertan), followed by 2nd magnitude Denebola to their east at the end of Leo’s Tail.
If you notice a particularly bright star far to the upper left of Denebola, it’s Arcturus in Boötes. Just 37 light-years away, this aging red giant appears particularly bright in our skies, and if it were at the center of our solar system, it would reach a quarter of the distance between the position of the Sun and Mercury.
Sunset: 8:10 p.m.
Moonrise: 12:53 p.m.
Moon setting: 11:46 p.m.
Moon phase: Wax crescent (42%)
friday august 5
The first quarter moon occurs this morning at 7:07 a.m. EDT.
With Saturn now just over a week away from opposition, let’s revisit the ringed planet in the evening sky to take stock. One hour after sunset, Saturn of magnitude 0.3 is 6° high and rising in the east, still near Deneb Algedi in Capricorn. Zoom in on the giant with a telescope and you’ll see that its disk extends 19″ across the equator and 17″ from pole to pole. Its beautiful ring system spans almost 43″ end to end.
Tonight, the planet’s largest moon, Titan, lies about 47 inches northeast of the planet, having passed through an upper conjunction earlier in the day. At magnitude 8.5, it should be easily visible through a telescope. Three magnitude 10 moons – Tethys, Dione and Rhea – all lie to the east of the planet. Tethys is closest to the rings, while Dione and Rhea sit farther away, about 1′ from the center of Saturn. Iapetus moves into western elongation on the 9th, when it will shine brightest, also reaching 10th magnitude.
Sunset: 8:09 p.m.
Moonrise: 2:03 p.m.
Moon setting: —
Moon phase: Waxing Gibber (53%)