The Evening Planets are on Parade and Deep Sky Objects are out, but it’s all about Meteors!
The Perseid Meteor Shower Peaks!
The prolific Perseid Meteor Shower peaks this year on Monday, August 13, so we can expect to see plenty of meteors all next weekend — and Monday night, too. Within a couple of nights before and after the peak date, the quantity will be reduced somewhat, but still worth looking for. We expect a fantastic show this year. The moon will reach its new phase two days before the predicted shower maximum. This means that the very slender crescent moon will set in the early evening and will not interfere at all with viewing this year’s display.
Meteor showers are annual events that occur when the Earth’s orbit passes through zones of debris left by multiple passes of periodic comets. (The analogy would be the material tossed out of a dump truck as it rattles along. The roadway gets pretty dirty if the truck drives the route a number of times!) Over the centuries, or longer, the dust-sized and sand-sized (or larger) particles accumulate and spread out a bit. When the Earth encounters them, the particles are caught by our gravity and burn up as they fall through our atmosphere at speeds on the order of 200,000 km/h. The duration of a meteor shower depends on the width of the zone, and the intensity depends on whether we pass through the densest portion, or merely skirt the edges.
The nickname for meteors is “shooting stars” or “falling stars”, but they bear no physical connection to the distant stars, and all your favorite constellations will look the same as ever at the end of the shower!
The source of the Perseids material is thought to be a 133 year period comet named Comet 109P/Swift-Tuttle. The active period for this shower is July 13 through August 26, so keep an eye out for them beyond this week. This shower is known for producing 60–80 meteors per hour at the peak — many manifesting as bright, sputtering fireballs!
While visible anywhere in the night sky, meteors will appear to radiate from a location in the sky (called the radiant) between the constellations of Camelopardalis (the Giraffe) and Perseus (the Hero), which gives this shower its name. The radiant is low in the northeastern sky during mid-August evenings — and nearly overhead by dawn. Meteor showers are best observed in the dark skies before dawn, because that’s the time when the sky overhead is plowing directly into the oncoming debris field, like bugs splatting on a moving car’s windshield. When the radiant constellation is overhead, the entire sky is available for observing.
The highest Perseid meteor rates this year are expected to occur on from Sunday night into Monday morning August 12–13, when the Earth will be the closest to the core orbit of comet 109P/Swift-Tuttle and its debris trail. If you begin to watch after dark on Sunday evening, you might catch very long meteors that are skimming the Earth’s upper atmosphere. These are fewer, but spectacular. As the night rolls on, the radiant of the meteors will rise higher in the sky, revealing more meteors because they are no longer hidden by the bulk of the Earth. The absolute best time to view is around 4 am local time when the radiant will be almost overhead and entire supply of meteors will be available for viewing.
For best results, try to find a safe and very dark viewing location with as much open sky as possible. Even a 30 minute drive to a park or rural site away from big city light pollution will help a lot. You can start watching as soon as it’s dark. Don’t worry about watching the radiant. Bring a blanket for warmth and a chaise to avoid neck strain, plus snacks and drinks. Try to keep watching the sky even when chatting with friends or family — they’ll understand. Call out when you see one; a bit of friendly competition is fun!
Don’t look at your phone or tablet — the bright screen will spoil your dark adaptation. If you can, minimize the brightness or cover the screen with red film. Disabling app notifications will reduce the chances of unexpected bright light, too. And remember that binoculars and telescopes will not help you see meteors because they have fields of view that are too narrow. Good hunting!
The Moon and Planets
The moon will spend this week in the pre-dawn sky as it heads towards its new phase on Saturday morning, August 11. At new moon, the moon is travelling between Earth and the sun. Since sunlight can only reach 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.
This new moon will feature a partial solar eclipse that will require proper eye protection to view. The Moon’s shadow for this partial solar eclipse will contact Earth at dawn in Labrador, Canada and sweep across Greenland, Iceland, and the North Pole, then southwards across northern Europe, Siberia and eastern Asia. Greatest eclipse occurs off the coast of northeastern Siberia at 09:46:15 UT, at which time 68% of the Sun will be obscured.
The day before, on Friday, August 10 at 2 pm EDT, the moon will reach perigee, its closest point to Earth for this month — a distance of 358,078 km. Because perigee occurs mere hours before the new moon, the combined gravitational tugs of the sun and moon pulling from the same direction in space will generate large tides on Earth over the following several days.
Extremely bright Venus will continue to catch our eye in the western evening sky this week — and it’s still brightening! The descending evening ecliptic is pulling Venus a bit lower each night, but we can observe it until about 10 pm local time. In a small telescope, the planet’s disk will resemble a first quarter moon, half-lit on the sunward side (although your telescope might flip the view).
We only have a few more good weeks to enjoy Jupiter this year. This week, the very bright planet will be visible in the southwestern sky after dusk, and then set in the west-southwest at about midnight local time. Every night, Jupiter is slowly shifting towards the bright star sitting just to its left. That’s Zubenelgenubi, the brightest star in Libra (the Scales). In binoculars, you’ll plainly see that Zubenelgenubi is a pair of stars. While you have the binoculars handy, see if you can see Jupiter’s four Galilean moons (Io, Europa, Callisto, and Ganymede) flanking the planet.
On Tuesday, August 7, Ganymede’s shadow will cross (transit) the northern portion of Jupiter’s disk from 8:53 pm (in twilight) to 10:37 pm — with a Great Red Spot bonus! A reasonable backyard telescope will show the black shadows, but a very good telescope is needed to see the moons themselves. More shadow transits are available in other time zones around the world, including some double shadow ones.
The Great Red Spot (or GRS, for short) takes about three hours to cross Jupiter’s disk. But the planet’s 10-hour rotation period (i.e., its day) means that the spot is only observable from Earth every 2–3 nights. If you’d like to see the GRS, use a medium-sized telescope (or larger). You’ll have your best luck on evenings with steady air — when the stars are not twinkling too much. Try to look within an hour before or after the following times: Tuesday, August 7 at 9:47 pm and Sunday, August 12 at 8:57 pm. All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone.
Medium-bright and yellow-tinted Saturn will be visible between dusk, when it’s shining about 2 fist diameters above the southern horizon, and 3 am local time, when it sets in the west. The ringed planet is situated just above the “lid” star of the Teapot-shaped constellation of Sagittarius (the Archer). The Milky Way is a little farther to the right (west). As the sky darkens, even a small telescope should be able to show you some of Saturn’s larger moons, especially Titan. Using a clock’s dial analogy, Titan this week will move counter-clockwise from a position at 4 o’clock (below the planet) to 12 o’clock (above it). (But your small telescope might flip and/or invert the view.)
Mars is still very bright and close to Earth this week. It will be rising at around 8:30 pm local time (give or take, depending on your latitude) and then climb until just after midnight local time, when it will reach an elevation of about 20° (or two outstretched fist diameters) above the southern horizon. (That will be the best hour to view the planet in a telescope because it will then be shining through the least amount of Earth’s distorting atmosphere.) Note that 20° is lower than many trees and buildings, so a clear southern vista is essential.
At visual magnitude 5.8, blue-green colored Uranus is visible between midnight and dawn without optical aid under very dark skies, or in binoculars and telescopes under moderately light-polluted skies. The ice giant planet is located in the eastern sky, about five finger widths to the left of the modestly bright star Torcular (Omega Piscium), which is above the “V” where the two starry cords of Pisces (the Fishes) meet.
Using a decent quality telescope, you can see the distant, blue planet Neptune, among the dim stars of Aquarius (the Water-bearer). This week, it will rise in the east before 10 pm local time. Look for the magnitude 7.8 planet sitting 1.5 finger widths to the right of the modestly bright star Phi (φ) Aquarii and about 4 finger widths to the left of the bright star Hydor (Lambda Aquarii).
Some Deep Sky Delights for New Moon Week
While the absent moon leaves our evening skies extra dark, here are some dimmer sights to track down in binoculars or telescopes.
The constellation of Lyra (the Harp) is positioned high overhead in the late evening during early August. The constellation features a stellar corpse and a number of easy double stars. While facing southeast, keen eyes might be able to see that the star Epsilon Lyrae, located just one finger width to the left (east) of very bright Vega (Alpha Lyrae), is a double star. Binoculars or a small telescope certainly will. Examination of Epsilon at high magnification will reveal that each of the stars is itself a double — hence its nickname, “the double-double”.
The stars at the top (northern) corners of Lyra’s distinctive parallelogram are also doubled. Nasr Alwaki (Zeta Lyrae), the star closer to Vega is a tight double. Delta Lyrae, at the other corner, is a visual double star. Aim your telescope midway between the stars Sulafat and Sheliak (another easy double star), which mark the lower (southern) end of Lyra’s parallelogram. Messier 57, also known as the Ring Nebula, will appear as a small, faint grey “smoke ring”. Higher magnification works well on this planetary nebula — the corpse of a star with similar mass of our sun.
Moonless nights are the perfect time to explore the countless knots and clumps of stars distributed along the Milky Way. Many of them were included in Charles Messier’s list of the sky’s best deep sky objects. Start by finding objects with binoculars, and then look at them using a telescope at low magnification. Particularly good star clusters include Messier 39 and Messier 29 in Cygnus (the Swan), the bright and large Wild Duck cluster (also known as Messier 11) and Messier 26, both located in Scutum (the Shield), and the Sagittarius Star Cloud (also known as Messier 24).
Astronomy Skylights for this week (from August 8th, 2018) by Chris Vaughan.
Keep looking up to enjoy the sky! I love getting questions so, if you have any, send me a note.