The New Moon brings Delightfully Dark Nights — Perfect for Looking at the night sky!
The Moon and Planets
This is the favorite week of the lunar month for skywatchers worldwide. The nights between Last Quarter and the New Moon are delightfully dark, and the mild temperatures will entice you outside to see the sights. Here are your Skylights!
The moon will begin the week as a pretty waning crescent that rises in the wee hours among the stars of Gemini (the Twins). That late-rising moon will remain visible during the daylight hours — well into the afternoon, in fact. Low in the east-northeastern sky, just before dawn on Wednesday morning, the delicate crescent of the old moon will land on the outskirts of the large open star cluster known as the Beehive and Messier 44 in Cancer (the Crab). The best viewing time will occur between about 4:30 and 5:30 am local time. If you place the moon in your binoculars, the cluster’s stars will be sprinkled below the moon (or above it, if you live south of the equator).
You can look for the very slim moon sitting low in the eastern sky before sunrise on Thursday morning. On Friday morning at 6:37 am EDT, the moon will reach its new moon phase. When new, the moon is travelling between Earth and the sun. Since sunlight is only reaching the far side of the moon, and the moon is in the same region of the sky as the sun, the moon will be completely hidden from view — from Earth.
The moon’s 27.32-day orbit around Earth is not circular, but elliptical — causing the moon to vary in distance by up to 6% (closer and farther) from the average Earth-moon distance of 385,000 lm. (That variation is responsible for producing occasional “supermoons”.) Because the moon’s closest approach to Earth (perigee) will occur only 5.5 hours after the moon’s new phase, the combined gravitational tugs of the sun and moon pulling from the same direction in space will generate large tides on Earth for several days.
The moon moves across the sky at a pretty high rate of speed — shifting by its diameter every hour. The fresh, young crescent moon will re-appear, low in the western evening sky after sunset, on Saturday evening. If you miss it, try again on Sunday, when the higher and thicker crescent will sit a fist’s diameter to the right (celestial northwest) of the bright star Spica in Virgo (the Maiden) before setting at about 9:30 pm local time.
Jupiter will continue to be the brightest object in the evening sky this week. As the sky begins to darken, look for the giant planet sitting less than a third of the way up the southern sky. Hour by hour, Jupiter will sink lower — then set in the west just after midnight local time. Jupiter is spending this summer above Scorpius (the Scorpion), in the southern part of Ophiuchus (the Serpent-Bearer).
On a typical night, even a backyard telescope will show you Jupiter’s two main equatorial stripes and its four Galilean moons — Io, Europa, Callisto, and Ganymede looking like small white dots arranged in a rough line flanking the planet. If you see fewer than four dots, then some of them are in front of Jupiter, or hidden behind it. Good binoculars will show the moons, too!
Over the next few nights, Jupiter will be passing very close to a dim, fuzzy patch of stars — a globular star cluster named NGC 6235 (from the New General Catalogue of deep sky objects). This collection of several hundred thousand stars, arranged by their mutual gravity into a densely packed sphere, is one of many such objects known to orbit our Milky Way galaxy. It is located 38,000 light years away from our solar system! When you see it, you are looking into the distant past. The light from those stars began traveling towards us around the time that Neanderthals died out! Jupiter is overwhelmingly bright compared to the cluster, so try hiding Jupiter just beyond your optics’ field of view. Remember that most telescopes will flip the view around — so check both to the left and right of the planet.
From time to time, the small, round, black shadows cast onto Jupiter’s surface by those four Galilean moons become visible in amateur telescopes as they cross (or transit) Jupiter’s disk. On Wednesday night from dusk to 9:30 pm EDT, observers in the Americas can watch Io’s small shadow transit Jupiter — with the Great Red Spot! On Thursday night from dusk to 9:40 pm EDT, observers in the Americas can watch Ganymede’s shadow transit the northern hemisphere of Jupiter.
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 on Monday evening from dusk to 10 pm EDT, on Wednesday night from 8:40 pm (in twilight) until 11:45 pm EDT, on Friday from 10:20 pm until Jupiter sets, and on Saturday after dusk.
Yellow-tinted Saturn is prominent in the southern evening sky, too — but it is less bright than Jupiter. The ringed planet will be visible from dusk until almost 2:30 am local time. Saturn’s position in the sky is just to the upper left (or celestial east) of the stars that form the teapot-shaped constellation of Sagittarius (the Archer). To find Saturn, look about 3 fist diameters to the left (east) of Jupiter. The Milky Way is between them.
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 arrange themselves above, below, or to either side of the planet. During this week, Titan will migrate counter-clockwise around Saturn, moving from the right of Saturn tonight (Sunday) to the upper left of the planet next Sunday. (Remember that your telescope will flip the view around.)
Tiny, blue Neptune will rise at dusk this week, and then it will climb the eastern sky until it reaches its highest point, due south, at about 2:20 am local time. The planet is among the stars of Aquarius (the Water-Bearer), sitting less than half a finger’s width to the left (celestial east) of a medium-bright star named Phi (φ) Aquarii. Both objects will appear together in the field of view of a telescope. Neptune is actually moving slowly toward that star and will “kiss” it in early September.
Blue-green Uranus will be rising in the east at about 10:30 pm local time this week; and it will remain visible all night long. Uranus is sitting below (celestial south of) 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 actually bright enough to see in binoculars and small telescopes, under dark skies — and it really does look blue! You can use the three modest stars that form the top of the head of the whale (or sea-monster in some tales) to locate Uranus for months to come — that’s because that distant planet moves so slowly in its orbit.
Bright and speedy little Mercury is very low in the east-northeastern pre-dawn sky — but it is descending sunward. Your best opportunity to see it comes early in the week in the minutes surrounding 6 am local time. Venus and Mars are out of action for now. They are snuggling up together in the sun’s glare.
Astronomy Skylights for the week of August 25th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!