This Week’s Sky at a Glance, August 17 – 25

 

Friday, August 17

• Once again, four bright planets remain in view as twilight fades all week. From right to left, they're Venus very low in the west-southwest, Jupiter in the southwest (upper left of Venus), Saturn in the south about as high as Jupiter, and bright Mars lower in the southeast. Best view: about 40 minutes after sunset.

• This evening the first-quarter Moon poses to the upper left of Jupiter. 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 all 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.

Sunday, August 19

• Now Antares is lower right of the Moon at nightfall, and Saturn glows to the Moon's left, as shown here.

Monday, August 20

• Saturn is the "star" left of the Moon this evening, as shown below right.

Tuesday, August 21

• Now Saturn glows to the Moon's right at dusk. And Mars shines farther to the Moon's lower left.

Wednesday, August 22

• The waxing gibbous Moon shines upper right of Mars this evening. Unlike Mars, the Moon lies in a nearly straight line with Saturn, Jupiter, and Venus (running from the right of the Moon very far to the west). To see how straight this line really is, hold a yardstick or a tightly stretched string along it. Why is this so? The Moon is nearly on the ecliptic tonight, but Mars is a good 6.1° south of the ecliptic.

Thursday, August 23

• Now Mars is lower right of the Moon, as shown above.

Friday, August 24

• After dark as August nears its end, the Great Square of Pegasus looms up in the east, balancing on one corner. Its stars are only 2nd and 3rd magnitude. Extending leftward from the Square's left corner is the main line of the constellation Andromeda, made of three stars (including the corner) about as bright as those forming the Square.

This whole giant pattern was named "the Andromegasus Dipper" by the late Sky & Telescope columnist George Lovi. Shaped sort of like a giant Little Dipper with an extra-big bowl, it currently lifts its contents upward.

Saturday, August 25

• Full Moon tonight and tomorrow (it's exactly full at 7:56 a.m. August 26th Eastern Daylight Time). This evening the Moon shines far left of Mars; they're on opposite sides of Capricornus.

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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.

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."

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This Week's Planet Roundup

Mercury is deep in the glow of sunrise.

Venus (magnitude –4.5) shines low in the west in twilight. In a telescope Venus is just on the crescent side of dichotomy (half-lit) and has grown to 26 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 gradually fading; it diminishes from magnitude –2.5 to –2.3 this week. On the other hand, it rises higher in the southeast earlier in the evening and is at its highest in the south around 11 p.m. daylight-saving time. (Although it's not very high for us mid-northern observers; it's at declination –26°, at the border of Capricornus and Sagittarius). Mars shrinks from 23 to 22 arcseconds wide this week, while the dust in its atmosphere continues to thin. Take advantage of Mars this large while you still 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 about 32° upper left of low Venus. Find Mars-colored Antares about 25° to Jupiter's left.

Saturn (magnitude +0.3, above the spout of the Sagittarius Teapot) glows yellow in the south at nightfall. It's about 23° left or upper left of Antares, and about 27° right or upper right of Mars.

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 midnight or 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

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