This Week’s Sky at a Glance, August 10 – 18

 

Radiant of the Perseid meteor shower

The Perseid meteors appear to stream away from the shower's radiant point near the border of Perseus and Cassiopeia. A shower's radiant is the perspective point where the meteors would all appear to come from if you could see them approaching in the far distance. In fact we see them only in the last second or two as they streak into Earth's upper atmosphere, and this can happen anywhere in your sky.

Friday, August 10

It's Perseid weekend! The annual Perseid meteor shower should peak late Sunday night August 12th. Already the meteors are increasing in number, and conditions this year are ideal. See Sunday below.

• Four bright planets remain in view at once during twilight all week. From right to left, they're Venus low in the west, Jupiter higher in the southwest, Saturn at about the same height in the south-southeast, and brilliant Mars low in the southeast. Best view: about 45 minutes after sunset.

Saturday, August 11

• The W of Cassiopeia, tilted by not very much, is up in the northeast these evenings above Perseus. The upper, right-hand side of the W is the brightest. Watch Cas rise higher and tilt further through the night and through the next few months.

• August is prime Milky Way time — if you have a dark sky. After nightfall is complete, the Milky Way now runs from Sagittarius in the south, up and left across Aquila and through the big Summer Triangle very high in the east, and on down through Cassiopeia to Perseus rising low in the north-northeast.

• New Moon (exact at 5:58 a.m. EDT August 11th).

Sunday, August 12

• The Perseid meteor shower should be at its peak tonight. Conditions are excellent; there's no moonlight, and the shower's predicted exact peak (usually lasting roughly 12 hours) falls during nighttime for Europe and North America.

You'll probably see the most meteors when the shower's radiant is high: from about midnight to dawn. With a really dark sky, you may see one or two meteors a minute on average during this time. There will be fewer in the evening, but the ones you do see when the radiant is low will be "Earthgrazers" skimming the upper atmosphere in long, graceful flight paths.

For more see the August Sky & Telescope, page 48, or SkyandTelescope.com.

Moon and Venus, Aug. 13, 14, 15, 2018

The thin crescent Moon waxes through Virgo whenever it's August.

Monday, August 13

• In twilight, spot the thin waxing crescent Moon very low in the west. Venus shines about a fist-width at arm's length to its left, as shown here. High above them shines Arcturus (out of the frame).

Tuesday, August 14

• The waxing crescent Moon shines over Venus in twilight. Closer to the moon is the telescopic binary star Gamma Virginis (Porrima), as shown here. Its twin components are currently 2.8 arcseconds apart.

Look left of the Moon for fainter Spica. Farther upper left of Spica shines bright Jupiter (out of the frame here). The Moon will march eastward above these celestial landmarks for the next three nights.

Pluto occults a star late tonight, and although the star is only magnitude 12.9 (Pluto is 14.2), amateurs with sufficiently large scopes and sensitive video setups will be doing their best to record it as will professionals. This is the brightest star Pluto has occulted since the New Horizons flyby in 2015, and recordings of the event could reveal any changes in the structure of Pluto's thin atmosphere as the little planetoid recedes year by year from the Sun. See the International Occultation Timing Association's page for this event. The predicted occultation zone includes most of the US and Mexico.

Wednesday, August 15

• Now the Moon hangs over Spica at dusk. Look lower right of them for bright Venus, and left or upper left of them for bright Jupiter.

Thursday, August 16

• The waxing Moon shines to the right of Jupiter. The bright yellow-orange star far to their upper right is Arcturus.

Friday, August 17

• First-quarter Moon (exact at 3:49 a.m. tonight EDT). Jupiter shines to its lower right. Antares is three times as far to the Moon's lower left.

• A mere 0.6° below Jupiter (about the width of a chopstick at arm's length) is 3rd-magnitude Alpha Librae, a wide double star for binoculars. Its fainter component, 4 arcminutes to the right of the bright one, is magnitude 5.1. That's only a little brighter than Jupiter's moons — which good binoculars will also show, lined up just to the big planet's left and right. Jupiter remains close to Alpha Librae through the coming week.

Saturday, August 18

• Lined up nearly vertically below the Moon this evening are the stars marking the head of Scorpius. Lower left of the Moon is brighter Antares, one of the brightest orange-red supergiant stars in the sky. Farther left of the Moon are Saturn, then bright Mars.

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Want to become a better astronomer? Learn your way around the constellations! They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Jumbo Pocket Sky Atlas cover

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Sample chart.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) and Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."


This Week's Planet Roundup

Dusty Mars on July 26, 2018

More surface markings on Mars are gradually becoming visible through the dust, though small, bright dust storms continue to kick up in the region of Solis Lacus (which is about 60% of the way from center to the 10 o'clock edge of this south-up view). Imager Damian Peach took this shot at 3:00 UT July 26th, when longitude 122° was on the central meridian.

Jupiter on July 27 (UT), 2018

Jupiter about as it appears now visually in a large amateur scope during excellent seeing. Sean Walker took this image on the evening of July 26th. Jupiter looks historically strange. Not only is the Great Red Spot extremely prominent, the normally bright Equatorial Zone has turned remarkably dusky.

Saturn on July 27 (UT), 2018

Saturn as it appears in a medium-size amateur telescope during excellent seeing. North is up. Note the Cassini Division in the rings, the bright Equatorial Zone on the globe and the darker South Equatorial Belt just above it, the shadier South Polar Region, and the dim gray C ring just inside the bright A and B rings. The C ring is most easily visible where it's in front of the globe. More than a month past Saturn's opposition, the shadow of the globe on the rings is clearly visible just off the globe's upper-left edge. S&T's Sean Walker took this image on the evening of July 26th.

Mercury is hidden in the glow of sunrise.

Venus (magnitude –4.4) shines low in the west during twilight. In a telescope Venus is at or very close to dichotomy (appearing exactly half-lit) and has grown to 23 arcseconds tall. For the best telescopic seeing catch Venus as early as you can, preferably long before sunset while it is still high.

Mars is beginning to fade very slightly, from magnitude –2.8 when it was closest to Earth around the turn of the month to –2.6 now. On the other hand, it rises higher in the southeast earlier in the evening. Mars is at its highest in the south around 11 or midnight daylight-saving time, though it's not very high at all for us mid-northern observers; it's at a very southerly declination (–26°) in southern Capricornus.

Mars also shrinks very slightly this week, from 24 to 23 arcseconds wide — really not enough to notice. The dust in its atmosphere continues to thin gradually, allowing faint, low-contrast views of dark surface markings. Take advantage of Mars this large while you can! It won't appear this big again until 2035.

For a Mars map that shows which side is facing Earth at your time and date, use our Mars Profiler.

Jupiter (magnitude –2.0, in Libra) shines in the southwest in twilight. It's between Spica about 20° to its lower right and the head of Scorpius nearly as far to its left.

Saturn (magnitude +0.2, above the spout of the Sagittarius Teapot) glows yellow in the south at nightfall, almost 30° to the right or upper right of much brighter Mars. In a telescope Saturn's rings remain tilted 26° to our line of night, After this year we won't see them so open again untuil nearly as open as we ever see them.

Uranus (magnitude 5.8, at the Aries-Pisces border) and Neptune (magnitude 7.8, in Aquarius) are well up in the east and southeast, respectively, by about 1 a.m. Finder charts for Uranus and Neptune.

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All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (also called UT, UTC, GMT, or Z time) minus 4 hours.

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"Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious."
— Stephen Hawking, 1942–2018

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"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
— Carl Sagan, 1996

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"Objective reality exists. Facts are often determinable. Vaccines save lives. Carbon dioxide warms the globe. Bacteria evolve to thwart antibiotics, because evolution. Science and reason are not a political conspiracy. They are how we determine facts. Civilization's survival depends on our ability, and willingness, to do this."
— Alan MacRobert, your Sky at a Glance editor

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"Facts are stubborn things."
— John Adams, 1770


2 thoughts on “This Week’s Sky at a Glance, August 10 – 18

  1. George Gliba

    It looks like the Perseid peak occurred a bit later than predicted on the 13th. I was observing
    last evening before midnight from 9:50 to 10:50 PM (01:50 to 02:50 UT Aug. 14th) and saw
    several beautiful grazers. I was out earlier than planned because it was clear and I was hoping
    to see a couple of Earth Grazers. Well, to my surprise there were several nice ones. Also, the
    rates seemed higher than expected. Unfortunately the clouds were a nuisance, but at least it
    stayed mostly clear until about 11:20 PM when it became very cloudy.

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