The Perseids Peak over Sunday Night, the Moon Returns to Grace the Eve, Jupiter Sports Twin Spots, and the Demon Star Revives!

Star Walk
8 min readAug 14, 2018
(Above: The path of Comet 21P/Giacobini-Zinner in the northeastern sky this week. It will be passing Casssiopeia heading downwards, shown here at 11 pm local time.)

The Perseid Meteor Shower

However, the spectacular annual Perseid Meteor Shower reached its peak on Sunday, the shower will taper off until it officially ends on August 26, so you should head out on Monday night if it’s clear, and continue to keep an eye out for bright meteors for the rest of this week, although the moon will increasingly affect seeing conditions. I wrote details about how meteor showers work here last week. Make an effort to see this show; next year the Full Moon will spoil the Perseid peak.

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 is dark — to catch very long meteors produced by particles skimming the Earth’s upper atmosphere. These are rare, but feature very long trains. Don’t worry about watching the radiant. Meteors from that position will be heading directly towards you and have very short trails.

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. I posted some diagrams here. Good hunting!

The Moon and Planets

After reaching its new phase on Saturday, the young crescent moon will return to grace the low western evening sky for a short time after sunset tonight (Sunday). For the rest of the week, it will wax and slide east, lingering longer after sunset each evening.

In the western sky on Tuesday evening, the moon will take up a position a palm’s width above bright Venus, making a lovely wide field photo opportunity. On Wednesday evening it will sit a similar distance above the bright white star Spica in Virgo (the Maiden). On Thursday and Friday, the moon will hop over Jupiter, moving from the planet’s upper right to its upper left. Using the moon as a starting point, you might be able to spot Jupiter in daylight using binoculars.

(Above: The moon and Jupiter in daylight at 7 pm EDT on August 16. The following day, the moon will hop to Jupiter’s upper left. Night Sky Chart made via Star Walk 2 iOS and Star Chart for Android.)

This is the best week of the moon’s monthly orbit to view it in binoculars or a telescope. The moon waxes because the sun is slowly rising over its eastern horizon. The shallow angle of the sunlight casts deep black shadows all along the terminator line — the boundary between the lit and unlit hemispheres. New terrain will be showcased every night!

Extremely bright Venus will still blaze away in the western evening sky this week — and it’s still brightening! On Thursday, Venus will reach its widest angle east of the sun. After that, the planet will begin to swing back towards a meeting with the sun in October. 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).

(Above: Venus reaches greatest elongation east of the sun on August 16, after which it will start to swing back towards the sun. Meanwhile the moon will look upon Jupiter as it passes close above the bright double star Zubenelgenubi,as shown here for 9 pm local time. Night Sky Chart made via Star Walk 2 iOS and Star Chart for Android.)

We only have a few more good weeks to enjoy Jupiter this year. This week, the very bright planet will be in the southwestern sky after dusk, and then set in the west-southwest at about 11:30 pm local time. Jupiter has been slowly shifting eastwards. In the middle of this week, it will pass close above a nearby bright star. Afterwards it will start to pull away. The star is 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.

From time to time, the small round black shadows cast by Jupiter’s four Galilean moons become visible in backyard telescopes as they cross (or transit) the planet’s disk. On Thursday, August 16, Europa’s shadow will begin to transit at 7:56 pm EDT (in evening twilight). At 8:05 pm EDT, Io’s shadow will join Europa’s and the duo will transit Jupiter until they both move off the planet at 10:10 pm. 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.

(Above: A double shadow transit caused by Europa and Io will occur on Jupiter on Thursday, August 16, as shown here at 9:15 pm EDT.)

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: Sunday, August 12 at 8:57 pm, Tuesday, August 14 at 10:36 pm, Friday, August 17 at 8:07 (in twilight), and Sunday, August 19 at 9:46 pm. All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone.

Around 9 pm local time, when the first bright stars appear overhead, medium-bright Saturn will appear not too high up the darkening southern sky. The yellow-tinted planet will reach its highest elevation of about 2 fist diameters above the southern horizon at around 9:30 pm, and then descend to set in the west at about 2:30 am. This summer, the ringed planet has been on the eastern (left-hand) outskirts of the Milky Way, and situated just above the “lid” star of the Teapot-shaped constellation of Sagittarius (the Archer). 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 will move counter-clockwise this week from a position at 12 o’clock (above the planet) to 7 o’clock (to the lower left of it). (Remember that your small telescope might flip and/or invert the view. Use the moon to find out how your telescope changes things.)

Mars will still be very bright and close to Earth this week. Visually, it will appear pink or orangey. It will rise over the southeastern horizon at around 8 pm local time (give or take, depending on your latitude) and then climb higher until 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.

(Above: Mars and Saturn dominate the overnight southern sky, as shown here for 10 pm local time this week. Tiny Pluto sits near Sagittarius, between the two naked-eye planets. Night Sky Chart made via Star Walk 2 iOS and Star Chart for Android.)

At visual magnitude 5.8, blue-green coloured Uranus is visible from late evening until dawn. You can see it 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 4.5 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.

(Above: The detailed positions of Uranus and Neptune in August, 2018.)

Using a decent quality telescope this week, you can see the distant and very blue planet Neptune among the dim stars of Aquarius (the Water-bearer). It will rise in the east shortly after 9 pm local time. Look for the magnitude 7.8 planet sitting 1.75 finger widths to the right of the modestly bright star Phi (φ) Aquarii and 4 finger widths to the left of the bright star Hydor (Lambda Aquarii).

At 1:36 am EDT on Wednesday, August 15, distant dwarf planet Pluto will pass in front of, or occult, a dim distant star. The planet is positioned roughly midway between Mars and Saturn. Many serious astronomers will try to record the event to study how Pluto’s atmosphere dims the star.

A Binocular Comet

Comet 21P/Giacobini-Zinner has been gradually brightening for some time because it is approaching Earth’s orbit. This week, you should be able to see the faint fuzzy object in binoculars or a small telescope, if you can escape city lights. The comet will be heading downwards every night past the bright star Segin, which marks the bottom-most star in the “W” of Cassiopeia (the Queen).

(Above: This animation was assembled from a series of 55 images of Algol taken with the CHARA interferometer at Mount Wilson Observatory, using the infrared part of the spectrum (coloring the normally white star red). It shows the dimmer companion star orbiting Algol and passing in front of it — a classic eclipsing binary star system. The numerical labels range from 0.0 at the start of the orbit, to 0.868, near the end of the orbit.)

See the “Demon” Star Brighten

The “Demon Star”, more formally known as Algol, is a star that is easy to see using unaided eyes. In Perseus (the Hero), it is among the most accessible variable stars for beginner skywatchers. Despite the connotation of its nickname (it represents the severed head of Medusa the Gorgon being held by Perseus), the star is a hot white star located 92 light-years from Earth.

Algol’s brightness dims noticeably for about 10 hours once every 2 days, 20 hours, and 49 minutes because a dim companion star orbiting nearly edge-on to Earth crosses in front of the much brighter main star — an arrangement that is called an eclipsing binary star system. On Saturday, August 18 at 9:32 pm EDT, Algol will reach its minimum brightness of magnitude 3.4 and will sit just above the northeastern horizon. By 2:30 am EDT, it will be halfway up the eastern sky and will have brightened to its usual magnitude of 2.1. The dimming periods can fall at any time of the day or night. The timing of this particular event makes watching the return to brightness a convenient project for evening observers.

Astronomy Skylights for this week (from August 12th, 2018) by Chris Vaughan.

Keep looking up to enjoy the sky! I love getting questions so, if you have any, send me a note.



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