This Week's Sky at a Glance, July 4 – 12

FRIDAY, JULY 4

■ You can still catch modest Mars and retiring Regulus glimmering low in the west as twilight fades toward night. Early in the week, they point down toward fading Mercury.

■ The Moon, two days past first quarter, shines in the west-southwest this evening a third of the way between Spica to its right and orange Antares twice as far to its left.

SATURDAY, JULY 5

■ The Big Dipper, high in the northwest after dark, is beginning to turn around to "scoop up water" through the evenings of summer and early fall.

■ Look low in the northwest or north at the end of these long summer twilights. Would you recognize noctilucent clouds if you saw them there? They're the most astronomical of all cloud types, what with their extreme altitude and, sometimes, their formation on meteoric dust particles. They used to be rare, but they've become more common in recent years as Earth's atmosphere changes. See Bob King's Nights of Noctilucent Clouds.

SUNDAY, JULY 6

■ This evening the waxing gibbous Moon shines in the head of Scorpius, with Delta Scorpii above it and Antares to its left. And tonight the Moon's dark limb occults Pi Scorpii, magnitude 2.9, for observers nearly all across North and Central America. See the July Sky & Telescope, page 48.

Map and timetables for the occultation. The first two tables, with predictions for many cities, are long. The first table gives the times of the star's disappearance behind the Moon's dark limb; the second gives its reappearance out from behind the Moon's bright limb (much less observable). Scroll to be sure you're using the correct table; watch for the new heading as you scroll down. The first two letters in each entry are the country abbreviation (CA is Canada, not California). The times are in UT (GMT) July 7th. UT is 4 hours ahead of Eastern Daylight Time, 5 hours ahead of CDT, 6 ahead of MDT, and 7 ahead of PDT.

For instance: Use the first table to see that for Chicago, Pi Scorpii disappears at 11:40 p.m. July 6th Central Daylight Time, when the Moon is 17° high in the south-southwest (azimuth 206°)

MONDAY, JULY 7

■ To casual starwatchers or those with an obstructed northern view, Cassiopeia in July might sound as wrong as Christmas in July. But already Cas has passed its lowest evening position of the year and is gradually gaining altitude in preparation for the coming fall and winter. Look for its flattened W shape low in the north-northeast after dark, no longer level.

TUESDAY, JULY 8

■ After nightfall, Altair shines in the east-southeast. It's the second-brightest star on the whole eastern side of the sky, after Vega high to its upper left.

Above Altair by a finger-width at arm's length is little orange Tarazed (Gamma Aquilae), Altair's eternal sidekick. It's a modest magnitude 2.7 compared to Altair's showy 0.7. But looks are deceiving. Altair looks so bright because it's one of our near neighbors, just 17 light-years away. Tarazed is an orange giant star about 380 light-years farther in the background — and it's 170 times as luminous as Altair!

WEDNESDAY, JULY 9

■ After nightfall, look due south for orange Antares nearly on the meridian. Around and upper right of Antares are the other, whiter stars forming the distinctive pattern of upper Scorpius. The rest of the Scorpion runs down from Antares toward the horizon, then left.

Three doubles at the top of Scorpius. The head of Scorpius — the near-vertical row of three stars upper right of Antares — stands nearly vertical. The top star of the row is Beta Scorpii or Graffias: a fine double star for telescopes, separation 13 arcseconds, magnitudes 2.8 and 5.0.

Just 1° below it is the very wide naked-eye pair Omega¹ and Omega² Scorpii. They're 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.

THURSDAY, JULY 10

■ Full Moon (exactly full at 4:37 p.m. EDT). The full Moon of July was traditionally called the Buck Moon in northeastern colonial America. Says the Old Farmer's Almanac, "At this time the antlers of bucks (male deer) are in full growth mode. This Native American name was noted by Captain Jonathan Carver during his travels in the 1760s."

■ More Scorpius: To the right of Antares is that roughly vertical row of Beta, Delta, and fainter Pi Scorpii. The middle one, Delta Sco, is the brightest — obviously so. But it didn't used to be. It used to be a trace fainter than Beta.

Delta is a strange variable star, a fast-rotating blue subgiant throwing off luminous gas from its equator. Assumed for centuries to be stable, Delta doubled in brightness unexpectedly in summer 2000, then dipped down and up again several times from 2005 to 2010, and has remained essentially steady at peak brightness (magnitude 1.7) ever since.

Delta has a smaller orbiting companion star that was suspected to trigger activity at 10.5-year intervals. Astronomers watched to see whether the system would have another flareup around 2022, when the companion star made its third pass by the primary star since 2000. But nothing happened. No one knows what might happen next, or when.

FRIDAY, JULY 11

■ One hour after sunset, as twilight is fading and the stars are coming out, you'll find the two brightest stars of summer, Vega and Arcturus, equally near the zenith: Vega toward the east, Arcturus toward the southwest (depending on your location).

SATURDAY, JULY 12

■ Vega is the brightest star in the eastern side of the sky. Three fists lower right of it is Altair, the second-brightest star in that region.

Above Altair by a finger-width at arm's length is little orange Tarazed (Gamma Aquilae), Altair's eternal sidekick. It's a modest magnitude 2.7 compared to Altair's showy 0.7. But looks are deceiving. Altair looks so bright because it's one of our near neighbors, just 17 light-years away. Tarazed is an orange giant star about 380 light-years farther in the background — and it's 170 times more luminous than Altair!

SUNDAY, JULY 13

■ Combine Vega and Altair with Deneb, less bright and about two fists lower left of Vega, and you've got the Summer Triangle.

■ Scorpius is sometimes called "the Orion of Summer" for its brightness, its blue-white giant stars, and its red supergiant. But Scorpius passes a lot lower across the southern sky than Orion does, for those of us at mid-northern latitudes. That means it has only one really good evening month: July.

The rich area around the tail of Scorpius is now at its highest in the south right after night is fully dark, as shown below. Find it lower right of the Teapot's spout by a fist at arm's length or less. Or about a fist and a half lower left of Antares. How high or low this whole scene will appear depends on how far north or south you live: the farther south, the higher.

Spot the two stars especially close together in the tail. These are Shaula and Lesath, Lambda and Upsilon Scorpii, also known as the Cat's Eyes. They're unequal and canted at an angle; the cat has a bleary eye and is tilting his head to the right. They're magnitudes 1.6 and 2.6. Both are blue-white supergiants, 700 and 500 light years away, respectively. The fainter one, Lesath, is the nearer one.

Between the Cat's Eyes and the Teapot's spout are the open star clusters M7 and especially M6, showy speckle-splashes in binoculars. M7 is the bigger and brighter one; M6 is more subdued.

Also: A line through the Cat's Eyes points west (right) by nearly a fist toward Mu Scorpii, a much tighter pair known as the Little Cat's Eyes. They're oriented almost exactly the same way as Lambda and Upsilon, but they're only 0.1° apart, so they appear as a single dot on the chart above; bring binoculars. They too are not a true binary. They're 800 and 500 light-years away, and again the fainter one is nearer.

This Week's Planet Roundup

Mercury is sinking back down out of sight into the glow of sunset.

Venus, brilliant at magnitude –4.1, rises above the east-northeast horizon a half hour or more before the first glimmer of dawn. Venus climbs higher until the dawn sky grows too bright. In a telescope Venus's shrinking globe (now only about 16 arcseconds pole to pole) has become gibbous, 65% sunlit.

Mars, magnitude 1.5 in Leo, glows low in the west in late twilight and sets soon after dark. Above it by a little more than a fist at arm's length is Denebola, Leo's tailtip, magnitude 2.1.

Jupiter, magnitude –1.9, is just beginning to emerge very low in the glow of sunrise. Late this week as dawn grows bright, try to find it about three fists to the lower left of Venus. See the July 12 view above.

Saturn (magnitude +0.9, in Pisces) rises around midnight daylight-saving time. Before and during early dawn, it's about five or six fists upper right of Venus.

The best time to try a telescope on Saturn is just before dawn, when Saturn has had time to get about 40° high while still in a dark or nearly dark sky. You may be surprised by the look of Saturn; its rings are nearly edge-on to us this year.

Uranus, magnitude 5.8, is still invisibly dim in the dawn background of Venus.

Neptune, a telescopic "star" at magnitude 7.9, lurks in Saturn's background just 1° from it. Catch this outermost major planet before dawn begins by using 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. Get everything planned out and ready to go the evening before, so that dawn doesn't outrun you.

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 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 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