The Sky This Week from July 29 to August 5

Wednesday, August 3
The slowly waxing Moon lies in Virgo this evening, not far from the stunning double star Porrima (Gamma [γ] Virginis). Through a telescope, this point of light splits into two of roughly equal magnitude: 3.65 and 3.56. According to Astronomy contributor Raymond Shubinski, “they look like two tiny headlights in space” about 3″ apart.

But back to the Moon, where we’ll focus on a bit of strange terrain in the lunar east (west on the sky). Along the lower left (western) edge of the Sea of Tranquillity lie several north-south wrinkle ridges that seem to really stand out under the low Sun angle. The nearly circular crater Arago boasts sharply defined walls, while to its west lies the half-buried Julius Caesar. Lunar researchers think that over time, lava welled up again and again in this region; one rim of Julius Caesar is lower than the other because of the sloping terrain where it formed, so only the higher portions of the crater rim remain easily visible. Just south of Julius Caesar is Rima Ariadaeus — a curious-looking crack that formed as the lunar surface pulled apart here.

Sunrise: 6:00 A.M.
Sunset: 8:11 P.M.
Moonrise: 11:46 A.M.
Moonset: 11:20 P.M.
Moon Phase: Waxing crescent (32%)

Thursday, August 4
Mercury passes 0.7° north of Regulus in Leo at 1 A.M. EDT. The pair is visible shortly after sunset, another 0.1° farther apart as they sink toward the western horizon. Mercury is now magnitude –0.5 and stands 4° high 30 minutes after sunset. You’ll need binoculars to find fainter Regulus (magnitude 1.4).

As the front half of Leo disappears in the growing dark, turn your attention east to the great cat’s hindquarters. Three stars here form a right triangle: 3rd-magnitude Chertan and Zosma (5° north of Chertan), followed by 2nd-magnitude Denebola to their east at the tip of the Lion’s tail.

If you notice a particularly bright star far to Denebola’s upper left, that’s Arcturus in Boötes. Just 37 light-years away, this aging red giant appears particularly bright in our sky and, if plopped into the center of our solar system, would reach a quarter of the way from the Sun’s position to Mercury.

Sunrise: 6:01 A.M.
Sunset: 8:10 P.M.
Moonrise: 12:53 P.M.
Moonset: 11:46 P.M.
Moon Phase: Waxing crescent (42%)

Friday, August 5
First Quarter Moon occurs this morning at 7:07 A.M. EDT.

With Saturn now just over a week from opposition, let’s revisit the ringed planet in the evening sky to take stock. An hour after sunset, magnitude 0.3 Saturn is 6° high and rising in the east, still near Deneb Algedi in Capricornus. Zoom in on the giant with a telescope and you’ll see that its disk stretches 19″ across the equator and 17″ from pole to pole. Its magnificent ring system spans nearly 43″ end to end.

Tonight, the planet’s largest moon, Titan, sits some 47″ northeast of the planet, having passed through superior conjunction earlier today. At magnitude 8.5, it should be readily visible through a telescope. Three magnitude 10 moons — Tethys, Dione, and Rhea — all lie east of the planet. Tethys is closest to the rings, while Dione and Rhea sit farther out, about 1′ from Saturn’s center. Iapetus is heading toward western elongation on the 9th, when it will shine at its brightest, also reaching 10th magnitude.

Sunrise: 6:02 A.M.
Sunset: 8:09 P.M.
Moonrise: 2:03 P.M.
Moonset: —
Moon Phase: Waxing gibbous (53%)