A Pretty Evening Moon, Pre-Perseids Meteors, and Aquila the Eagle Soars in the East!
The Perseids Meteor Shower is Building
The prolific Perseids Meteor Shower is already building, so keep an eye out for a few of them this week. The almost full moon will spoil the show on the peak nights of August 12/13, so take advantage of the darker skies this week.
To increase your chances of seeing any meteors, find a dark location with lots of sky, preferably away from light polluted skies, and just look up with your unaided eyes. Binoculars and telescopes are not useful for meteors because their fields of view are too narrow to fit the streaks of meteor light. Don’t watch the radiant. Any meteors near there will have very short trails because they are travelling towards you. Try not to look at your phone’s bright screen — it’ll ruin your night vision. And keep your eyes heavenward, even while you are chatting with companions. I’ll write more about the Perseids next week. For now, happy hunting!
The Moon and Planets
This week, the moon will grace the evening sky worldwide as it waxes in phase and swings away from the sun. In the process, it will pay Jupiter a visit, and then end the week next to Saturn. It’s also the best week of the lunar month to view the moon because the sunlight reaching the moon is coming in shallowly from the east — casting deep shadows to the east of even the slightest topographic elevation. Gorgeous vistas in binoculars and telescopes run pole-to-pole along the moon’s terminator — the line that separates the lit and dark hemispheres. As a bonus, the slowly rising sun shifts the terminator west every night. Here are your Skylights for this week!
After sunset tonight (Sunday), look for a very pretty, delicate crescent moon shining in the western sky for a short time after dusk. On Monday, the moon will be higher and farther from the sun. The bright white star Spica in Virgo (the Maiden) will be positioned a palm’s width to the moon’s lower left (celestial south).
On Wednesday the moon will complete the first quarter of its orbit around Earth, when the relative positions of the Earth, sun, and moon cause us to see it half-illuminated — on its eastern side. At first quarter, the moon always rises around noon and sets around midnight, so it is also visible in the afternoon daytime sky.
On Thursday evening, the waxing moon will pass through dim Libra (the Scales) and land above the line of three modest stars that form Scorpius’ pincers. On Friday, the waxing gibbous moon will land 1.5 finger widths to the upper left (northeast) of the bright planet Jupiter. If you glance at the moon and Jupiter over several hours, starting at dusk, you will see the moon’s orbit carry it farther from the planet.
In the southeastern sky after dusk on Sunday evening, the bright, waxing gibbous moon will be positioned four finger widths to the right of the bright, yellowish planet Saturn. The pair will cross the sky together for most of the night and will easily appear together within the field of binoculars. Once again, if you watch them over several hours, starting at dusk, you will see the moon’s orbit carry it closer to the planet and the rotation of the sky lift Saturn higher than the moon. Observers in eastern Indonesia, most of Australia, northern New Zealand, Melanesia, and Polynesia (except Hawaii) will see the moon occult Saturn on August 12.
This week, Jupiter will continue to outshine the stars. After dusk, look for Jupiter in the southwestern sky. It will set in the west at about 1:30 am local time. On a typical night, even a backyard telescope will show you Jupiter’s two main equatorial stripes and its four Galilean moons, named Io, Europa, Callisto, and Ganymede. The moons always form a rough line flanking the planet. If you see fewer than four, then some are in front of Jupiter, or hidden behind it.
Due to Jupiter’s rapid 10-hour rotation period, the Great Red Spot (or GRS) is only observable from Earth every 2nd or 3rd night, and only during a predictable three-hour window. The GRS will be easiest to see using a medium-sized, or larger, aperture telescope on an evening of good seeing (steady air). If you’d like to see the Great Red Spot in your telescope, it will be crossing the planet tonight (Sunday evening) from dusk to 11:30 pm EDT, on Tuesday night from 10:30 pm to 12:30 am EDT, after dusk on Friday, and from 10 pm to midnight EDT next Sunday.
Yellow-tinted Saturn will remain visible from dusk until about 4 am local time. The ringed planet’s position in the sky is just to the upper left (celestial east) of the stars that form the teapot-shaped constellation of Sagittarius (the Archer). Saturn is quite a bit dimmer than Jupiter. To find it, look about 3 fist diameters to the lower left (east) of Jupiter. Dust off your telescope! Once the sky is dark, even a small telescope will show Saturn’s rings and several of its brighter moons, especially Titan! Because Saturn’s axis of rotation is tipped about 27° from vertical (a bit more than Earth’s axis), we can see the top surface of its rings, and its moons can appear above, below, or to either side of the planet. During this week, Titan will migrate counter-clockwise around Saturn, moving from the lower left of Saturn tonight (Sunday) to the right of the planet next Sunday. (Remember that your telescope will flip the view around.)
Tiny blue Neptune is in the southeastern sky in late evening, among the stars of Aquarius (the Water-Bearer). The planet will be rising shortly before 10 pm local time this week. You’ll find the magnitude 7.8 Neptune sitting a thumb’s width to the left (east) of a medium-bright star named Phi (φ) Aquarii. The planet is actually moving slowly toward that star!
Blue-green Uranus will be rising just before midnight local time this week. It is sitting below the stars of Aries (the Ram) and is just a palm’s width above the head of Cetus (the Whale). At magnitude 5.8, Uranus is bright enough to see in binoculars under dark skies.
This week, Mercury is in the northeastern pre-dawn sky — below the stars of Gemini (the Twins). It will continue to climb away from the sun this week. Your best opportunity to see it will land between 5 and 5:30 am local time.
Venus and Mars are lost in the sun’s glare for the next while.
Aquila the Eagle
Look halfway up the southeastern sky in early August evenings, and you’ll easily spot the bright, white star Altair, sitting at the bottom corner of the Summer Triangle asterism. Altair is the brightest star in the venerable constellation of Aquila (the Eagle) and marks the great bird’s head. The eagle’s body and tail extend downwards to the right, more or less following the Milky Way. The wings extend upwards and downwards.
Aquila so clearly resembles a bird that many cultures have seen the same pattern in its stars, including the Babylonians. In Greek mythology, it was the eagle that held Zeus’ thunderbolts. The Romans called it Vultur volans “the flying vulture”. The Hindus associated the stars with the half eagle-half human god Garuda.
Classic Chinese poetry told a well-known story about the Weaver Girl and the Cowherd, one of the four great folktales. In this tale, Zhinü 織女 the weaver girl was in love with Niulang 牛郎 the cowherd. To prevent their forbidden love, they were banished to the heavens, and Zhinu, represented by the nearby bright star Vega, and Niulan, represented by Altair, were separated by the Silver River, or Milky Way. Two small stars visible on either side of Altair represent their children. In the story, once a year on the 7th day of the 7th month, a flock of magpies would form a bridge, reuniting the lovers for one day only.
Altair is Arabic for “flying eagle”. The star itself is a yellow-white star about ten times larger than our Sun, and only a mere 17 light-years away, making it the twelfth brightest star in the night sky. At 10 hours, its rotation rate is one of the fastest known, spinning so rapidly that the star has an oblate shape (wider at the equator than it is tall). In the sky, Altair is symmetrically flanked by two small stars named Alshain and Tarazed. Because the three stars resemble a weighing balance, their names are derived from the Arabic phrase for one, “shahin-i tarazu”. The trio span about three finger widths, or 5° of separation. Tarazed, on the right, is an interesting star. It is a cool, orange giant star located 460 light-years away and shining at almost 3,000 times the luminosity of our Sun; and it emits an abundance of X-rays!
The rest of Aquila’s stars are dimmer, but nonetheless visible to unaided eyes. Almost a fist’s diameter to the lower right of Altair is the star Delta Aquilae, representing the body. The wings are each about a fist diameter in length. The upper wing has the star Okab at the tip. The lower wing is formed by two widely spaced stars named Almizan I and Almizan II. (Some apps use the designations Eta and Theta Aquilae.) The eagle’s tail is marked by a pair of small stars a finger’s width apart. The brighter tail star is named Al Thalimain “the two ostriches”. The Pioneer 11 spacecraft launched in 1973 is coasting towards this star, with an arrival time of about 4 million years!
Sweep your binoculars though the area around Aquila to see an abundance of stars from the nearby galactic plane. About a palm’s width below the eagle’s tail, you’ll easily spot another avian object — The Wild Duck Cluster or Messier 11 — a famous bright open cluster. Good “hunting”!
Astronomy Skylights for the week of August 4th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!
