A Morning Moon and a Meteor Shower, Jupiter Cruises Past a Cluster, and Some Southerly Sights!
(Above: This week, Jupiter’s apparent orbital motion will carry it from left to right past a globular star cluster designated NGC 6235. The planet, its moons, and the star cluster will all fit into the field of view (simulated here by the circular view) of a backyard telescope at high power, especially around their closest pairing, which will occur on Saturday night. I’ve flipped the view to match most refracting telescopes.)
Hello, Summer Stargazers!
Here are your Astronomy Skylights for the week of July 21st, 2019 by Chris Vaughan. Feel free to pass this along to your friends and send me your comments, questions, and suggested topics. I repost these emails with photos at http://astrogeoguy.tumblr.com/ where all the old editions are archived. You can also follow me on Twitter as @astrogeoguy! Unless otherwise noted, all times are Eastern Time. Please click this MailChimp link to subscribe to these emails. If you are a teacher or group leader interested joining me on a guided field trip to York University’s Allan I. Carswell Observatory or the David Dunlap Observatory, visit www.astrogeo.ca.
I can bring my Digital Starlab inflatable planetarium to your school or other daytime or evening event. Contact me, and we’ll tour the Universe together!
Southern Delta Aquariids Meteor Shower
The Southern Delta Aquariids meteor shower runs annually from July 21 to August 23. It is caused by the Earth passing through a cloud of tiny particles dropped by a periodic comet – likely Comet 96P/Machholtz and the shower will peak before dawn on Sunday, July 28, but is quite active for a week surrounding that date. This shower commonly generates 15-20 meteors per hour at the peak, but is best seen from the southern tropics, where the shower’s radiant, in Aquarius, is positioned higher in the sky. The waning crescent moon on the weekend should not adversely affect the shower very much.
To increase your chances of seeing 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. Happy hunting!
(Above: The Southern Delta Aquariids Meteor Shower will peak on the coming weekend, July 27-28. The best time for viewing will be before dawn, when the radiant will be higher. The waning crescent moon will not interfere with your hunt.)
The rest of July will bring us dark evening skies worldwide. That’s because the moon will be rising after midnight and waning in phase and brightness. So grab your bug spray and binoculars, or dust off the old telescope, and set up in a spot with a low and open southern horizon. I’ll tour you through the scorpion, the teapot, and the shield in this week’s Skylights!
Tonight, the waning gibbous moon (i.e., more than half illuminated) will rise at about midnight local time. For the rest of the week, the moon will shift eastward and wane in phase while it slides towards next week’s meeting with the sun. The moon will be rising later every night, but the night-to-night difference will be much less than the usual 40 to 50 minutes. That’s because the angle between the eastern horizon and the moon’s orbit is smaller at this time of the year.
From Tuesday to Saturday before dawn, the moon’s orbit will carry it just above Cetus (the Whale), flying like a drone from the beast’s tail to his head. On Friday morning, the pretty crescent moon will sit about two finger widths to the upper left of the main belt asteroid Vesta. Look for a medium-bright star named Lambda Ceti sitting about four finger widths to the right of the moon. Vesta will be located a small distance below, and about halfway along, a line joining the moon and that star. Vesta will be visible as a little pinpoint in binoculars and telescopes.
(Above: As shown here for Friday, July 26 at 4 am local time, the waning moon will be positioned near the major asteroid Vesta. The shallow angle that the ecliptic (yellow) and the moon’s orbit (red) make with the eastern horizon will cause the moon to rise only about 20 minutes later on each consecutive morning.)
On Saturday morning, the crescent moon will land a palm’s width to the upper right (celestial west) of the big triangle of stars that form Taurus the Bull’s face. People in Asia and Australia can see the moon pass directly through those stars, including the bright, orange star Aldebaran, which marks the bull’s angry southern eye. When skywatchers in the Americas see the moon again on Sunday morning, it will be positioned to the lower left (celestial east) of Aldebaran.
Keep an eye out for the moon in the morning daytime sky this week. On Wednesday it will reach its last quarter phase, when its western half is illuminated. Last quarter moons always rise around midnight and remain visible in the southern sky all morning. They are positioned ahead of the Earth in our trip around the sun. About 3½ hours later, Earth will occupy that same location in space.
The planets are spread along the Ecliptic (which closely expresses the plane of our Solar System) from sunset to sunrise. Reddish Mars has been steadily fading from view as it slips downward towards the evening sun. Your best chance to see Mars is to look low in the north-northwestern sky for a short time after 9 pm local time.
(Above: Every days Mars is sinking lower into the western evening sunset, as shown here at 9:15 pm local time.)
Jupiter is the extremely bright, white object shining in the southern evening sky. This week, Jupiter will be visible from dusk until almost 3 am local time. Even a backyard telescope can show Jupiter’s two main equatorial stripes and the 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 either in front of Jupiter or hidden behind it.
Jupiter will do something interesting this week, and then it will repeat it a month from now! On the evenings surrounding Friday, July 26, Jupiter’s orbital motion will carry it close past a globular star cluster designated NGC 6235, which is located in the southern sky in the constellation of Ophiuchus (the Serpent-Bearer). At closest approach on July 26, the bright planet will sit only 4 arc-minutes above the cluster. (For comparison purposes, the full moon is 30 arc-minutes across.) You can start looking for the cluster starting tonight. It will be located to Jupiter’s right (celestial west), but your telescope will flip the directions around.
That star cluster is located about 38,000 light-years away, while Jupiter will only be 38 light-minutes from Earth! Both objects will fit within the field of view of a backyard telescope at medium power. To better see the dim, fuzzy globular cluster, try placing the bright planet just outside your field of view. Binoculars might work, too – if your sky is very dark!
From time to time, the small, round black shadows cast by the Galilean moons become visible in amateur telescopes as they cross (or transit) Jupiter’s disk. On Tuesday night, Europa’s small shadow will be transiting the northern part of Jupiter from 11:45 pm to 2 am EDT. On Wednesday night, Ganymede’s larger shadow will be transiting the northern part of Jupiter from 11:30 pm to 1:45 am EDT. On Saturday, July 27, Io’s mall shadow will cross from 10:50 pm to 1 am EDT, with the Great Red Spot joining the fun after 11:45 pm.
(Above: On Tuesday night, Europa’s small shadow will be transiting the northern part of Jupiter from 11:45 pm to 2 am EDT, as shown here at 11:55 pm EDT. Your telescope will likely flip and/or mirror the view shown here.)
Speaking of the spot, 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 Tuesday evening from 8:30 to 11:30 pm EDT and on Thursday night from 10:15 pm to 1:15 am EDT.
(Above: Jupiter events for the next month. Blue times are Galilean Moon shadow transits. Red times are Great Red Spot appearances. The actual viewing window spans about 90 minutes before and after those times.)
Yellow-tinted Saturn will remain visible all night long this month. Its 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 below Saturn tonight (Sunday) to the upper right the planet next Sunday. (Remember that your telescope will flip the view around.)
For night owls, distant and dim, blue Neptune is in the southeastern pre-dawn sky, among the stars of Aquarius (the Water-Bearer). The planet will be rising before 10:30 pm local time this week. You’ll find the magnitude 7.9 Neptune sitting a thumb’s width to the left (east) of a medium-bright star named Phi (φ) Aquarii.
(Above: The two Ice Giant planets Uranus and Neptune are visible after late evening, as shown here at 1 am local time.)
Blue-green Uranus will be rising at about 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.
In a similar situation to Mars, Venus is barely bright enough to see within the pre-dawn twilight sky that surrounds it. It is sitting very low in the northeastern sky - sinking ever-closer to the rising sun. Venus will be rising at about 5:30 am local time all week. By the end of the week, Mercury will climb over the horizon to join Venus. The swift innermost planet will become easier to see next week.
(Above: Towards the end of this week, Mercury will ascend to sit to the right of descending Venus, both low in the eastern pre-dawn sky, as shown here for 5:40 am local time. Mercury is just beginning a good period of visibility.)
Touring the Dark July Southern Sky
With the moon rising after midnight and waning in phase and brightness, let’s grab bug spray and binoculars, or dust off the old telescope, and set up in a spot with a low and open southern horizon – for a tour through the scorpion, the teapot, and the shield!
Once it’s getting nice and dark, face south and look for the Milky Way rising from the southern horizon between Jupiter and Saturn. (Those two planets will only be embracing the Milky Way this summer. They’ll move east of it next year.) Due to haziness near the horizon, and more of Earth’s intervening atmosphere, The Milky Way will be easier to see higher in the sky, where it passes directly through Cygnus (the Swan). By midnight local time, the great swan will be nearly overhead. The rest of the Milky Way will descend to the northeast. It thins as it passes through the “W” of Cassiopeia (the Queen) and Perseus (the Hero) because that area represents the outer edge of our galaxy’s disk.
Looking due south again - in late July, the distinctive constellation of Scorpius (the Scorpion) reaches its peak elevation over the southern horizon after dusk. Jupiter is spending this year in the sky just northeast of that constellation’s brightest star, orange-tinted Antares, the “Rival of Mars”. Three white, medium-bright stars aligned in a roughly vertical line to the west of Antares mark the creature’s claws today – however the major stars of neighboring Libra (the Scales) used to take that role. The rest of the scorpion extends to the south, curling eastward into the Milky Way, and terminating in a bright double star named Shaula, which marks the poisonous stinger. Observers above mid-northern latitudes will struggle to see the southerly stars of the constellation. For Moana fans, the Maori people of New Zealand consider those same stars to represent Maui’s fish hook pulling the Milky Way up every night!
(Above: In late July and early August annually, the Milky Way appears to rise from the southern horizon, like steam from the Teapot-shaped constellation of Sagittarius, the Archer. The southern sky, shown here at 10:30 pm local time, is riddled with interesting deep sky objects visible in binoculars and backyard telescopes when the sky is dark. Each coloured symbol represents a good target. Dotted circles are open star clusters, circles with crosshairs are globular clusters, and green symbols are nebulas.)
For contrast with cool, reddish Antares, look at the two hot, white stars, both named Al Niyat, that flank the red supergiant. Magnitude 3.1 Al Niyat I (also known as Sigma Scorpii) is located 2 finger widths to the upper right of Antares. It is a B1-class star with a surface temperature of 36,200 K. Magnitude 2.8 Al Niyat II is located 2.25 degrees to the lower left of Antares. Also known as Tau Scorpii, it is a B0-class star with a surface temperature of 30,000 K. At 734 light-years from the sun, Al Niyat I is nearly twice as far away as Al Niyat II. Use binoculars to find a fuzzy patch that is sitting just a finger’s width to Antares’ lower right. It is a globular star cluster named Messier 4.
Late July evenings bring us one of the best asterisms in the sky, the Teapot in Sagittarius (the Archer). This informal star pattern features a flat bottom formed by the stars Ascella on the left and Kaus Australis on the right, a triangular pointed spout pointing right, marked by the star Alnasl, and a pointed lid marked by the star Kaus Borealis. The stars Nunki and Tau Sagittarii form its handle. The asterism is low in the sky, but it reaches maximum height above the southern horizon around midnight local time, when it will look as if it’s serving its hot beverage – with the steam rising as the Milky Way. By the way – the centre of our galaxy is located just 4.5 finger widths to the upper right of Alnasl!
(Above: The bright planets Jupiter and Saturn are spanning the Milky Way this summer, as shown here at 10:30 pm local time this week. Scorpius, the Scorpion sits to the right (celestial west) of Sagittarius. Small Scutum, the Shield, is above Sagittarius.)
Next, use your binoculars to explore the rich star fields and nebulae sprinkled along the Milky Way above Sagittarius. The bright star clusters known as Ptolemy’s Cluster (also designated Messier 7), the Sagittarius Star Cloud (Messier 24), and Messier 25 will appear as compact, bright, white clouds in binoculars. You can also look for the bright knots of nebulosity comprising the Lagoon Nebula (Messier 8), the Omega / Swan Nebula (Messier 17), and the Eagle Nebula (Messier 16). Higher up, you’ll discover more good clusters, including Messier 39 and Messier 29 in Cygnus, Caldwell 16 in Lacerta (the Lizard), the Wild Duck cluster (Messier 11) and Messier 26 in Scutum (the Shield). Use your backyard telescope for a closer look!
Scutum (the Shield) was created by Johannes Hevelius in 1683 by taking some of the stars from next-door Aquila (the Eagle). The small constellation (84th out of 88 by area) occupies some prime celestial real estate along the summertime Milky Way. Scutum, which reaches its highest position over the southern horizon at midnight local time in late July, has a background of rich star fields, which are overlain by some fine open star clusters, including the aforementioned Wild Duck Cluster. Use binoculars to trace out the dim stars that form the constellation and then follow up with your telescope.
Public Astro-Themed Events
Every Monday evening, York University’s Allan I. Carswell Observatory runs an online star party - broadcasting views from four telescopes/cameras, answering viewer questions, and taking requests! Details are here. On Wednesday nights they offer free public viewing through their rooftop telescopes. If it’s cloudy, the astronomers give tours and presentations. Details are here.
On Tuesday, July 23, starting at 7 pm, U of T’s AstroTour planetarium show will be Grand Tour of the Cosmos. Find tickets and details here.
On Thursday, July 25, starting at 7 pm, U of T’s AstroTour planetarium show will be The Life and Death of Stars. Find tickets and details here.
The next RASC Family Night at the David Dunlap Observatory will be on Saturday, August 10. There will be sky tours in the Skylab planetarium room, space crafts, a tour of the giant 74” telescope, and viewing through lawn telescopes (weather permitting). The doors will open at 8:30 pm for a 9 pm start. Attendance is by tickets only, available here. If you are a RASC Toronto Centre member and wish to help us at DDO in the future, please fill out the volunteer form here. And to join RASC Toronto Centre, visit this page.
Keep looking up, and enjoy the sky when you do. I love questions and requests - so, send me some!
