The Perseids Peter out, an Aging Moon Moves into Morning with Mercury, and Jupiter Gleams near a Globular!
The Perseids Meteor Shower Peaks!
The prolific Perseids Meteor Shower peaked last Tuesday-Wednesday. The active period for this shower runs until August 26, so keep an eye out for a few stragglers this week. Next year, the moon will once again interfere with this shower. But 2021 will bring us a fantastic, moonless Perseids shower.
The Moon and Planets
This week, the moon will depart the evening sky all over the world while it wanes in phase — leaving our nights darker, and ideal for treasure hunting. Meanwhile, Jupiter and Saturn will continue to put on a show in the southern sky. Here are your Skylights for this week!
For the first few half of this week, the waning gibbous moon (i.e., more than half-illuminated) will rise in late evening and pass through the modest sea constellations of Cetus (the Whale) and Pisces (the Fishes).
In the southern pre-dawn sky on Wednesday, the moon will be positioned a palm’s width below (to the celestial southeast of) the distant, blue-green planet Uranus. Look for a modestly-bright star to the upper left of the moon. That star is Xi Ceti, also known as Al Kaff al Jidhmah (spellings vary). Slow-moving Uranus will remain about four finger widths above (or celestial northeast of) Xi Ceti for the next several months, allowing you to locate Uranus in binoculars and telescopes after the bright moon moves away. (More on this below.)
On Friday afternoon, the moon will reach its last quarter phase. At last quarter, the moon, half-illuminated on its western side, always rises around midnight local time worldwide and remains visible in the southern sky all morning — or the northern sky, if you live south of the Equator.
When the moon rises at about 12:30 am local time on Friday night, it will be traveling through the stars that form the large, triangular, sideways face of Taurus (the Bull). The very bright, warmly-tinted star positioned about two finger widths below the moon will be Aldebaran. This orange-giant star represents the bull’s eye. To end the week, overnight on Saturday, and into Sunday morning, the waning crescent moon will land near the medium-bright star Zeta Tauri, which marks the lower, eastern horn tip of Taurus.
Jupiter will return to being 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 before 1 am local time. Jupiter is spending this summer 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!
Here’s a fun exercise on the next clear night once the sky is nice and dark. Grab your binoculars or telescope at low magnification and look just a fraction of a finger’s width to the left (celestial east) of Jupiter for a dim, fuzzy patch. What you are seeing is a globular star cluster, a mass of thousands of stars arranged by their mutual gravity into a densely packed sphere. This cluster, one of hundreds known to orbit our Milky Way galaxy, is named NGC 6235 (from the New General Catalogue of deep sky objects). 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 moving steadily towards that cluster, and will pass in front of it next Monday. So the later in the week you look, the closer Jupiter will be to the cluster. 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 Monday night from 11:02 pm to 1 am EDT, observers in the Americas can watch Io’s small shadow transit Jupiter, although Jupiter will set in the GTA before the transit is complete. On Saturday night from 11:30 pm to 1:55 am EDT, observers in the Americas can watch Europa’s shadow transit the northern hemisphere of Jupiter — but Jupiter will again set during mid-transit for observers in the GTA.
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) after 11:15 pm EDT, on Wednesday night from 7:45 pm (in twilight) until 10:45 pm EDT, and on Friday from 9:15 pm to 12:15 am EDT.
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 about 3 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 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 will be rising soon after dusk and then it will climb the eastern sky until it reaches its highest point, due south, at about 2:45 am local time. The planet is among the stars of Aquarius (the Water-Bearer), sitting half a finger’s width to the left (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 shortly before 11 pm local time this week; and it will be 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.
Because it rises earlier every night, Uranus is transitioning into a good, evening target. As I mentioned above, you can use the three stars that form the top of the head of the whale (or sea-monster in some tales) to locate Uranus for months to come — since the planet moves so slowly in its orbit.
This week, Mercury is low in the east-northeastern pre-dawn sky in Cancer (the Crab) — and below the bright stars of Gemini (the Twins). The planet is now descending sunward again. Your best opportunity to see it this week falls between 5:15 and 6 am local time.
Venus and Mars are lost in the sun’s glare for the next while.
Some Dark-Sky Delights
With the moon gone and the sky darker, grab your binoculars and tour the Milky Way — from the southern horizon where it rises like steam from the Teapot-shaped stars of Sagittarius (the Archer), overhead through the great Summer Triangle bird constellations of Aquila (the Eagle) and Cygnus (the Swan), and then down to the northeastern horizon — through the W-shaped constellation of Cassiopeia (the Queen).
If you are away from city lights, look for the dark lanes of interstellar dust that divide up the Milky Way. That dust prevents the visible-wavelength light produced by the billions of stars within the plane of our home galaxy from reaching us.
As you scan around, look for bright knots of stars. Larger ones are open star clusters — groups of stellar siblings that have been “recently” born together and are still traveling through the galaxy as a family. (Most stars in the night sky were originally born in groups by the collapse of enormous cold, dark hydrogen clouds.) The small clusters could be open star clusters that are farther away from us, or perhaps, more globular clusters!
Take note of where you find the clusters and look for them on a sky chart — from a magazine like SkyNews, a website, or an astronomy app. I’ll highlight some more delights next week when the moon is approaching its new phase.
Astronomy Skylights for the week of August 18th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!