This Week's Sky at a Glance, July 29 – August 6

FRIDAY, JULY 29

■ The Big Dipper hangs diagonally in the northwest after dark. From its midpoint, look to the right by about three fists at arm's length to find Polaris (not very bright) glimmering due north as always.

Polaris is the end of the Little Dipper's handle. The only other Little Dipper stars that are even moderately bright are the two forming the outer end of its own bowl: 2nd-magnitude Kochab and 3rd-magnitude Pherkad. Find them to Polaris's upper left, by about a fist and a half at arm's length, one over the other. They're called the Guardians of the Pole, since they ceaselessly circle around Polaris through the night and through the year.

SATURDAY, JULY 30

■ Face southeast after darkness is complete. Look a little more than halfway from horizontal to overhead, and there's Altair, the brightest star in that immediate area.

A finger-width above it is its little sidekick identifier Tarazed (Gamma Aquilae), two magnitudes fainter and far in the background. Tarazed is actually 100 times more luminous than Altair — it's an orange giant — but it's 390 light-years away compared to Altair's distance of just 17 light-years.

■ Look left of Altair by a bit more than a fist for compact little Delphinus, the Dolphin, leaping leftward in the edge of the Milky Way.

Closer to Altair's upper left is Sagitta the narrow Arrow, smaller and dimmer than Delphinus. The arrow points left. Binoculars help with both.

SUNDAY, JULY 31

■ The False Comet. Lower Scorpius is on the meridian right after dark, offering us northerners our best view of this rich region. A favorite binoculars sight here is the False Comet, a curving spray of stars extending almost 2° up from Zeta Scorpii. In photos, an emission nebula adds to the scene.

To find Zeta Sco: From bright Antares, follow the constellation pattern of the Scorpion lower left and downward by four stars to where the pattern jogs left. That's Zeta. In the August Sky & Telescope Matt Wedel writes, "To the naked eye [in a dark sky] the stars and clusters can look remarkably like a comet, but binoculars of any magnification will explode that illusion into a wonderland of suns." See his Binocular Highlight column on page 43 of that issue, with chart.

MONDAY, AUGUST 1

■ Three doubles at the top of Scorpius. Meanwhile, much higher at the other end of Scorpius — atop the vertical row of three stars to the right of Antares — stands Beta Scorpii or Graffias: a fine double star for telescopes, separation 13 arcseconds, magnitudes 2.8 and 5.0.

Just 1° lower left of Beta is the very wide naked-eye pair Omega¹ and Omega² Scorpii. They point roughly back to Beta. The two Omegas are 4th magnitude and ¼° apart. Binoculars show their slight color difference; they're spectral types B9 and G2.

Upper left of Beta by 1.6° is Nu Scorpii, separation 41 arcseconds, magnitudes 3.8 and 6.5. In fact it's a telescopic triple. High power in good seeing reveals Nu's brighter component itself to be a close binary, separation 2 arcseconds, magnitudes 4.0 and 5.3, aligned almost north-south.

■ We're hardly halfway through summer, but already Cassiopeia is getting well up after dark. Look for its tilted W pattern in the north-northeast.

High above Cas is dimmer Cepheus. Below it, the head of Perseus is poking up. The farther north you live the higher they will appear.

■ And when is the exact midpoint point of summer? Halfway from the June solstice to the September equinox. This year it works out to be at 1:09 a.m. August 7th Eastern Daylight Time (5:09 August 7th UT). That minute is the exact center-balance of astronomical summer: the very top of the circle of the year as defined by the astronomical seasons.

For the Northern Hemisphere, that is. It's the exact bottom of winter for the Southern Hemisphere.

TUESDAY, AUGUST 2

■ Arcturus dominates the high western sky after dark. Spot the Big Dipper off to its right, in the northwest.

In astronomy lore today, Arcturus may be best known for its cosmic history: It's a Population II orange giant some 7 billion years old, older than the solar system, racing by our part of space on a trajectory that indicates it came from another galaxy: a dwarf galaxy that fell into the Milky Way and merged with it.

But in the astronomy books of our grandparents, Arcturus had a different claim to fame: It turned on the lights of the 1933 World's Fair in Chicago, celebrating "a century of progress." Astronomers rigged the newly invented photocell to the eye end of big telescopes around the US and aimed the scopes where Arcturus would pass at the correct moment on opening night. In places where the sky was clear the star's light crept onto the photocells, the weak signals were amplified and sent over telegraph wires to Chicago, a switch was tripped, and on blazed the massive lights to the cheers of tens of thousands.

Why Arcturus? Astronomers of the time thought its was 40 light-years away (modern value: 36.7 ±0.2 light-years). So the light would have been in flight since the previous such great event in Chicago, the World's Columbian Exhibition in 1893.

And earlier? Arcturus was known as the first of the nighttime stars to be seen in the daytime with a telescope: by Jean-Baptiste Morin in 1635.

WEDNESDAY, AUGUST 3

■ Mercury is very low in the west in bright twilight this week. This evening you can use binoculars, or better a telescope, to seek both Mercury and fainter Regulus close by it. You'll have only a narrow time window, if any, between the sky being too bright and the elusive pair being too low. Good luck.

■ The thick crescent Moon shines in the southwest at nightfall. Look below it, by about 3°, for Spica.

■ You probably know that the Big Dipper's curved handle "arcs to Arcturus." But the arc of the handle itself, extended to include the adjacent side of the Dipper's bowl, guides the way to another landmark. Fairly near the focus of that longer arc (the center of the circle that the arc would be part of) is 3rd-magnitude Cor Caroli, Alpha Canum Venaticorum. This is a lovely double star for small telescopes: colors white and pale yellow-white, separation a generous 23 arcseconds.

THURSDAY, AUGUST 4

■ The Moon is nearly first quarter. More than a fist to its lower right at the end of dusk, look for Spica getting low. Closer in the opposite direction from the Moon is Alpha Librae, a wide binocular double star. Its components are currently almost horizontal. The fainter one (magnitude 5.1) is to the right of the brighter one (mag 2.8), by a chasm of 281 arcseconds.

FRIDAY, AUGUST 5

■ First-quarter Moon (exact at 7:07 a.m. on this date EDT). After dark the Moon shines in central Libra. Delta Scorpii and then brighter Antares are to its left, Spica is farther to its lower right, and Arcturus shines even farther to the Moon's upper right.

SATURDAY, AUGUST 6

■ Now the Moon shines in the head of Scorpius. Look for orange Antares just to its left and Delta Scorpii just to its right (during evening for the longitudes of the Americas).

 

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This Week's Planet Roundup

Mercury is very low in the glow of sunset. About 30 minutes after sunset, try scanning for it with binoculars just above the horizon a little to the right of due west (one or two fists at arm's length). Good luck. At least Mercury is pretty bright: roughly magnitude –0.5 all week.

Venus, magnitude –3.9 in Gemini, continues to rise just as dawn begins. As dawn brightens, look for it low in the east-northeast. It's far below Capella.

Mars, magnitude +0.2 in Aries, rises around midnight or 1 a.m. and shines high in the east-southeast as dawn begins. It rises about four fists lower left of bright Jupiter. By dawn they're high in the south, with Mars now directly left of Jupiter.

Mars is still small in a telescope, 8 arcseconds in apparent diameter.

Jupiter rises due east around 10 or 11 p.m, shining at a bright magnitude –2.7 at the Pisces-Cetus border. It's highest in the south (transiting) as dawn begins. In a telescope Jupiter is now a good 45 arcseconds wide.

Saturn, magnitude +0.4 in western Capricornus, is nearing its August 13-14 opposition. It's very low in the east-southeast in late twilight, higher in the southeast in late evening, and at its highest and best in the south around 1 a.m. Saturn's rings appear roughly as wide, end to end, as Jupiter's disk.

Uranus, magnitude 5.7 in Aries, is in the background of Mars this week.

Neptune, magnitude 7.9 at the Aquarius-Pisces border, is high in the south before the first light of dawn, west of Jupiter.

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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 and graphics that also depend on longitude (mainly Moon positions) are for North America.

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

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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 magazine of 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) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet as to charts on paper.

You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) 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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Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the heavens above. It's free.

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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

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

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