This Week's Sky at a Glance, August 22 – 31

FRIDAY, AUGUST 22

■ As summer wanes and bright Arcturus moves down the western sky, the kite pattern of Boötes that sprouts from Arcturus leans over to the right. The kite is narrow, slightly bent, and 23° long: about two fists at arm's length. Arcturus is its bottom point, from which the stubby kite tail hangs down.

The Big Dipper poses to its right in the northwest at about the same height as Arcturus, as shown below.

SATURDAY, AUGUST 23

■ As August proceeds and nights begin to turn chilly, the Great Square of Pegasus looms up in the east, balancing on one corner. Its stars are only 2nd and 3rd magnitude. Your fist at arm's length fits inside it. Saturn glows down to its lower right.

From the Square's left corner, the backbone of the constellation Andromeda extends to the lower left: three stars in a slightly curving line (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. It's shaped sort of like a giant Little Dipper with an extra-big bowl. It's currently lifting its contents upward.

To make its handle even longer and the whole thing shaped more like a giant Little Dipper, extend the handle onward to Alpha Persei, shown above.

■ The actual Little Dipper, meanwhile, is tipping over leftward in the north. It's only 40% as long as the Andromegasus Dipper as drawn above, and most of it is much fainter. As always, you'll see that it's oriented more than 90° counterclockwise compared to Andromegasus; it's dumping its contents out.

■ New Moon (exact at 2:07 a.m. on this date EDT).

SUNDAY, AUGUST 24

■ The W of Cassiopeia is tilted up in the northeast these evenings, above Perseus. The upper right-hand side of the W is its brightest side. Watch Cas rise higher and straighten upright through the next two hours and, equivalently, the next month. The rule to remember for the turning of the sky: Looking two hours later is the same as looking one month later. Why? Answer is in footnote 1 at the bottom of this page.

MONDAY, AUGUST 25

■ While twilight is still fairly bright, can you catch the very thin Moon, not quite two days old, very low in the west-southwest? Bring binoculars. The Moon can help guide you to increasingly elusive Spica and Mars, as shown below.

TUESDAY, AUGUST 26

■ Now the Moon is about equidistant between Spica and Mars, as shown above.

■ The brightest star high in the southeast these moonless nights is Altair, with little orange Tarazed above it by a finger-width at arm's length.

A little more than a fist-width to Altair's left is delicate Delphinus, the Dolphin, leaping left.

Above Altair, slightly less far, is smaller, fainter Sagitta, the Arrow. It too points leftward. You'll need a nice dark sky. Or binoculars.

WEDNESDAY, AUGUST 27

■ A winter preview: Step out before the first light of dawn any time this week, and in addition to Venus and Jupiter lighting the east, the sky will display the same starry panorama you'll be seeing at dinnertime come January. Orion is striding up in the southeast, with Aldebaran and then the Pleiades high above him. Sirius sparkles far down below Orion. The Gemini twins are lying on their sides well up in the east, though right now their heads Pollux and Castor are quite outdone by the Jupiter and Venus combo. By winter those planets will be very much elsewhere.

THURSDAY, AUGUST 28

■ Back to Aquila. One of the brightest Cepheid variable stars in the sky — a naked-eye, glance-up-to-check-it variable just waiting for you — is Eta Aquilae.

Never heard of it? It's 8° south of Altair and pulses from magnitude 4.3 to 3.4 and back every 7.18 days. That's slightly more than a doubling of brightness, then a halving. As with other classical Cepheids its rise to maximum is faster than its fade to minimum. Its period is so close to a week that you'll find it repeating itself on the same weekdays for a month or two at a time.

Judge its brightness by comparing it between Theta Aquilae, magnitude 3.2; Delta Aql, mag. 3.4; Beta Aql; mag. 3.7; and Iota Aql, mag. 4.4. They're all part of Aquila's flying-eagle stick figure. See the comparison-star chart in Bob King's "Summer Nights with Eta Aquilae" in the August Sky & Telescope, page 50.

FRIDAY, AUGUST 29

■ Saturn is the brightest dot low in the east right after dark. But as evening advances, it gets competition. Fomalhaut, the Autumn Star, makes its appearance above the southeast horizon some three fists to Saturn's lower right. Its rising time will depend on where you live. But by 11 p.m. now, you should have no trouble identifying Fomalhaut low in the southeast if you have a good view in that direction. No other 1st-magnitude star is anywhere near there.

Saturn and Fomalhaut are magnitudes +0.7 and +1.2, respectively. And can you see that one twinkles more than the other?

■ As dawn brightens on Saturday morning the 30th, Jupiter, Venus, and low Mercury form a tall, nearly equally spaced straight line in the east, as shown below.

SATURDAY, AUGUST 30

■ First-quarter Moon (exactly so at 2:25 a.m. EDT tonight). The Moon shines in the southwest right after nightfall, in the head of Scorpius. Look for orange Antares about 5° to the Moon's upper left. Lesser Delta Scorpii, the second-brightest star in the area, is a similar distance to the Moon's upper right (for North America).

SUNDAY, AUGUST 31

■ Now Antares and Delta Sco line up to the right of the Moon.

This Week's Planet Roundup

Mercury is visible very low in the east-northeast as dawn grows bright. Its location is easy enough to find; Jupiter and Venus point down to it, as shown in the illustration above. Mercury continues to swell in brightness, from magnitude –0.5 to –1.2 this week.

Venus and Jupiter, both of them in or near Gemini, shine in the east before and during dawn. They're the two brightest planets, currently magnitudes –3.9 and –2.0 respectively. They went through a close conjunction on August 12th, just under 1° apart. By Saturday morning the 23rd they've widened to 11° apart. A week later on the 30th they'll be 18° apart. Both are about at their farthest from Earth, so don't expect much in a telescope.

Mars, a weak magnitude 1.6 in Virgo, still glimmers very low in the west during evening twilight. Binoculars will help. Mars sets at twilight's end. It too is about at its farthest from Earth.

Don't confuse orange Mars with brighter, whiter, twinkly Spica to its upper left. Mars and Spica are 14° apart on Friday the 22nd, narrowing to 1o° by Friday the 29th.

Saturn (magnitude +0.7 in Pisces) rises due east in twilight. It's lower right of the Great Square of Pegasus, which stands on one corner diamond fashion. The Square's lower left side points diagonally down almost straight to Saturn. See the second illustration from the top of this page.

But the best time to observe Saturn with a telescope is in early morning hours when it's high toward the south. We see Saturn's rings almost edge-on this year, and the Sun shines on them from nearly our direction too. So the rings and their shadow combine to form a thin black line along Saturn's equator.

Uranus (magnitude 5.7, in Taurus near the Pleiades) rises around 11 p.m. and gets high in the east in the early morning hours. In a telescope it's a tiny but definitely non-stellar dot 3.6 arcseconds wide.

Neptune, a telescopic "star" at magnitude 7.8, lurks 1½° from Saturn. Use the finder chart for Neptune with respect to Saturn in the June Sky & Telescope, page 51. With a pencil, put a dot on the path of each of the two planets for your date. Neptune is just 2.3 arcseconds wide.

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. UT is also known as UTC, GMT, or Z time.

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 a more detailed 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.

For the attitude every amateur astronomer needs, read Jennifer Willis's Modest Expectations Give Rise to Delight.

Once you get a telescope, to put it to good use you'll need a much more detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas, in either the original or Jumbo Edition. Both show all 30,000 stars to magnitude 7.6, and 1,500 deep-sky targets — star clusters, nebulae, and galaxies — to search out among them.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many, as well as many more deep-sky objects. It's currently out of print, but maybe you can find one used.

The next up, once you know your way around well, are the even larger Interstellarum atlas (with 201,000+ stars to magnitude 9.5 and 14,000 deep-sky objects selected to be detectable by eye in large amateur telescopes), and Uranometria 2000.0 (332,000 stars to mag 9.75, and 10,300 deep-sky objects). And read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet (which many observers find more versatile) 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. The pinnacle for total astro-geeks is the new Annals of the Deep Sky series, currently at 11 volumes as it works its way forward through the constellations alphabetically. So far it's up to H.

Can computerized telescopes replace charts? Not for beginners I don't think, and not for scopes on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting finicky technology to work rather than learning how to explore the sky. 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 and a curious mind." Without these, "the sky never becomes a friendly place."

If you do get a computerized scope, make sure that its drives can be disengaged so you can swing it around and point it readily by hand when you want to, rather than only slowly by the electric motors (which eat batteries).

However, finding faint telescopic objects the old-fashioned way with charts isn't simple either. Do learn the essential tricks at How to Use a Star Chart with a Telescope.

Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the naked-eye heavens above. It's free.

"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; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence."
            — John Adams, 1770

1. Why, in the ever-changing constellation panorama, is looking two hours later the same as looking one month later?

Because the direction in space you look when you face into the night sky depends on two things: Earth's own 24-hour rotation, and where Earth's night side — the side away from the Sun — faces during the Earth's 12-month orbit around the Sun. So, looking one month later turns your night-direction view as much as looking two hours later on a given night.