Morning Venus Brushes the Bull’s Brow, and Lay Down and Look Up for Stars!
Lay Down and Look Up!
The best way to take in the splendor of the night sky is to lay on your back and gaze upwards, where the sky is darkest and the air thinnest. This is also your best bet to spot meteors and passing satellites. Some easy to recognize constellations are positioned directly overhead in late evening this month.
Position yourself so that south is below your gaze, i.e., chin towards south horizon and the crown of your head towards the North Star Polaris. Your left shoulder will point east and your right one west. Looking up, just east of straight overhead you will find the bright white star Vega in Lyra (the Harp). Vega, the western corner of the Summer Triangle, is the brightest star in our summer nights and the fifth brightest in all the sky.
Shifting your gaze a short distance west of Vega you will find the constellation of Hercules, whose body is defined by a keystone shaped quartet of modestly bright stars. The keystone is about 6° across (a palm’s width), with the wide end north and the narrow end south. The hero of mythology is upside down for us. His sharply bent legs extend northward and his two arms are outstretched to the southeast and southwest. His eastern hand star (to our lower left) combines with four others to make a loose chain of five stars running left-right, each separated by a couple of finger widths. In classical drawings he is grasping the three-headed dog Cerberus, which he was tasked with capturing as one of his twelve labours.
Hercules is the fifth largest constellation in area, and was one of the original 48 constellations tabulated by Ptolemy. It contains one of my favorite objects, the globular cluster known as the Great Hercules Cluster or Messier 13. This object is a tightly packed ball of about 300,000 old stars. At magnitude 5.9, it is visible with unaided eyes under dark skies as a faint smudge, but reveals much more under magnification! It is located along the western (right) edge of the keystone, about one-third of the way from the wide end. Roughly between his knees there is another smaller globular cluster called Messier 92. We can’t see them visually, but Hercules is home to several known exoplanets orbiting his stars.
Hercules contains quite a few double and binary stars within reach of a backyard telescope. One of the nicest is modest Rasalgethi, or Ras Algethi “Head of the Kneeler”, which sits about 16° to the southwest (lower right) of the bottommost corner of the keystone (almost into Ophiuchus). In a small telescope, this star easily splits into a lovely pair of orange and greenish stars. The slightly brighter one is a red giant class star that varies in brightness randomly over months to years. The partner is a yellow Sun-like star that is itself a binary star too tightly spaced to resolve. The stars are about 360 light-years away and are orbiting one another with a period of 3,600 years. This double star, like many others, was given a single name centuries before telescopes revealed that there was more than one star there.
The brightest star in Hercules, Kornephoros “Club-bearer”, sits a fist’s width below the bottom right star of the keystone (just extend that side of the stone downwards). Only 3° (about two finger widths) to its lower right, is the double star Gamma (γ) Herculaneum, sometimes called Nasak Shamiya III. This is another pair that easily splits into two yellow stars in a modest telescope. But this double is an optical illusion. The fainter star is actually much closer to us!
Marsic “the Elbow”, or Kappa (κ) Herculaneum, is another “line of sight” double star that’s easy in a small telescope. It’s 4° to the lower right of Gamma Herculaneum. A few degrees further down brings us to the triangular head of Serpens (the Serpent), but that’s another story.
Immediately to the west of Hercules is a very distinctive constellation called Corona Borealis (the Northern Crown), and for good reason! A circle of seven stars forms a tiara festooned by a single bright star called Alphekka or “jewel”. The constellation is approximately a palm’s width across. In mythology, the crown was given to Princess Ariadne of Crete by Dionysus, who married her years after she helped Theseus escape the Minotaur. It, too, is one of the original Ptolemaic constellations. The Mikmaq people of Canada saw it as the den of the great celestial bear, while other cultures saw a string of jewels, a boomerang, and an eagle’s nest.
Most of Corona Borealis’ unaided-eye stars are variable. Alphekka is a hot, blue-white star 78 light-years away and similar in nature to Vega and winter’s Sirius, which are much closer. It is also an eclipsing binary star, in which a smaller orbiting companion star passes in front of the main star every 17.3 days, causing the combined light output to dim slightly. Astronomers have detected a dust disk around the star that might indicate that a new solar system is being formed.
The bright star further west of the crown is Arcturus. The fourth brightest star in the entire night sky, Arcturus means “Guardian of the Bear” in Greek, because it rises after Ursa Major (the Big Bear), which sits to its upper right (west). Arcturus is that colour because it is just passing middle-age for a star, starting on its way towards the red supergiant stage. In Chinese, Arcturus is known as Dà Jiǎo 大角, “Great Horn”.
Sun, Moon, and Planets
The full moon, known as the “Buck Moon”, “Thunder Moon”, or “Hay Moon” occurred in the wee hours this morning (Sunday, July 9), so it will rise with a bit shaved off its eastern (our right) side on Sunday evening. Full moons always rise around sunset and set around sunrise, and the July one always sits near the Teapot-shaped constellation of Sagittarius.
For the rest of the week, the moon rises later — lingering into daytime morning skies, while it wanes towards Last Quarter next Sunday afternoon. Next weekend’s post-midnight waning moon leaves the evening sky darker. We can start to look out for early Perseid meteors. The Earth enters its debris field starting July 13. The peak won’t occur until next month, though.
Mercury continues to be visible for northern hemisphere observers this week. It sets about 10 pm local time, but the best time to look for it is shortly before 9:45 pm. It will be less than a palm’s width above the western horizon, south of where the sun went down, and will be the brightest object in that area of sky.
Extremely bright Venus is rises in the eastern sky about 3 am local time and remains an eye-catching beacon until dawn. This week, it travels eastwards above the stars that make up the triangular face of Taurus (the Bull), passing within three finger widths above the bright orange-ish star Aldebaran in mid-week. Viewed in a telescope around now, the planet presents a more than half illuminated phase. It will be in the morning sky for a few more months while becoming easier and easier to view.
Saturn is the bright yellowish object visible low in the southeastern sky after the evening sky darkens. It crosses due south (at its highest elevation of 24°) after 11 pm local time, and then sets in the west before dawn.
Jupiter is the extremely bright object in the southwestern evening sky this week. It sets about 12:30 am local time. The planet’s four large Galilean moons are easily visible in a small telescope. A larger telescope will also show the round black shadows they cast when they cross (or transit) the planet — and the Great Red Spot. Here are the best events in Eastern Daylight Savings Time. (Simply add or subtract the appropriate hours to convert them to your time zone.)
On Wednesday, July 12, Io’s shadow will transit from dusk until 10:51 pm. On Sunday, July 16, Ganymede’s shadow will transit near Jupiter’s north pole from 10:17 pm until the planet sets (about 12:15 am). The Great Red Spot is visible on Jupiter for about three hours centred on Monday, July 10 at 8:44 pm (in twilight), Wednesday, July 12 at 10:24 pm, and on Saturday, July 15 at 12:03 am (while setting).
Distant Pluto, which resides among the stars of Sagittarius (the Archer), reaches maximum visibility for the year on Sunday, July 9. But at magnitude 14, it’s out of reach of all but the largest telescopes. The nearby full moon won’t help matters, but I posted a diagram here.
Stargazing News for this week (from July 9th) by Chris Vaughan.
