Science

This Week’s Sky at a Glance, July 24 – August 1 – Sky & Telescope

Comet NEOWISE: Still there at dusk. . . . Comet NEOWISE continues to hang dimly in the northwest at the end of twilight, though it’s fading. Plan to look 1½ to 1¾ hours after your local sunset time, just as twilight ends. The comet was down to 4th magnitude as of July 23rd, but its increased altitude has put it in a better viewing position.

Bring binoculars. The receding comet is about 15° or 20° or more to the lower left or left of the Big Dipper’s bowl. That’s about 1½ to 2 two fists at arm’s length or more. For this week you can extrapolate the daily comet positions on the graphic below, or use this more detailed finder chart as NEOWISE crosses the hind legs of Ursa Major and moves into Canes Venatici. (On that chart its positions are shown for 0:00 Universal Time, which falls in the late afternoon or evening of the previous date for the time zones of North America.)

For more info and lots of pix, see Bob King’s Comet NEOWISE Dazzles at Dusk and the NEOWISE section of our readers’ photo gallery.

This week you’re better off looking for Comet NEOWISE at least 1½ hours after your local sunset time, at the end of twilight, not 1 hour. And extrapolate the daily comet symbols here out to your date (these are civil dates for North America). The blue 10° scale at top right is about the width of your fist held at arm’s length.

FRIDAY, JULY 24

■ As summer progresses, bright Arcturus moves down the western side of the evening sky. Its pale ginger-ale tint always helps identify it.

Arcturus forms the bottom point of the Kite of Bootes. The Kite, rather narrow, extends upper right from Arcturus by 23°, about two fists at arm’s length. The top of the kite is bent slightly down, as if something banged it.

All this summer, there’s no missing Jupiter and Saturn on any starry evening. Jupiter is the brightest point in the evening sky.Mercury is having a moderately good apparition low in the dawn this week and next. Locate it far lower left of brilliant Venus. And almost straight below Venus (depending on your latitude), can you spot twinkly orange Betelgeuse emerging up into the dawn glow?

SATURDAY, JULY 25

■ The Moon shines in the west-southwest as the stars come out. Look for Spica sparkling about a fist to its left. Almost three times as far above the Moon is brighter Arcturus.

■ The Sagittarius Teapot is in the south these evenings; find it right of Jupiter and Saturn. With the advance of summer, the Teapot is starting to tilt and pour from its spout to the right. The Teapot will tilt farther and farther for the rest of the summer — or for much of the night if you stay out late.

■ The tail of Scorpius is lower right of the Teapot, by hardly a fist at arm’s length. How low this whole scene is depends on how far north or south you live: the farther south, the higher.

Look for the two stars especially close together in the tail. These are Lambda and fainter Upsilon Scorpii, known as the Cat’s Eyes. They’re canted at an angle; the cat is tilting his head and winking.

Between the Cat’s Eyes and the Teapot’s spout are the open star clusters M6 and especially M7, showy in binoculars.

A line through the Cat’s Eyes points west (right) by nearly a fist-width 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. Can you resolve the Mu pair without using binoculars? It takes sharp eyes!

SUNDAY, JULY 26

■ First-quarter Moon tonight and tomorrow. (It’s exactly first-quarter at 8:33 a.m. July 27 EDT). The Moon appears just a trace larger than average; it was at perigee two nights ago.

Tonight Spica is below the Moon. Arcturus is high above, to their upper right.

MONDAY, JULY 27

■ Now Spica is two fists lower right of the Moon . Closer to the Moon’s lower left (for North America) is the wide binocular double star Alpha Librae (Zubenelgenubi), magnitudes 2.8 and 5.1, separation 331 arcseconds.

TUESDAY, JULY 28

■ We’re not yet halfway through summer, but already W-shaped Cassiopeia, a constellation of fall and winter evenings, is climbing up in the north-northeast as evening grows late. And the Great Square of Pegasus, emblem of fall, rises to balance on one corner just over the eastern horizon.

WEDNESDAY, JULY 29

■ As the stars come out, spot orange Antares below the gibbous Moon. To their left is the head of Scorpius, a near-vertical row of three slightly lesser, whiter stars.

The top star of the row is Beta Scorpii or Graffias, a fine double star for telescopes, separation 13 arcseconds.

Just 1° below Beta is the very wide, diagonal 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.

Left of Beta by 1.6° is Nu Scorpii, another fine telescopic double, separation 41 arcseconds. Or rather, a triple. High power in good seeing reveals Nu’s brighter component itself to be a close binary, separation 2 arcseconds and aligned almost north-south.

All these double-star targets are bright enough that the light of the Moon close by shouldn’t be a problem (barring thick summer haze).

THURSDAY, JULY 30

■ The two brightest stars of summer are Vega, nearly overhead after the night is fully dark, and Arcturus shining in the west. (Brighter Jupiter in the southeast doesn’t count!) Draw a line down from Vega to Arcturus. A third of the way along it, the line crosses the dim Keystone of Hercules. Two thirds of the way to Arcturus it crosses the dim semicircle of Corona Borealis with its one modestly bright star, Alphecca or Gemma.

Vega and the star of the Keystone closest to it form an equilateral triangle with Eltanin to their north, the nose of Draco the Dragon. Eltanin is the brightest star of Draco’s quadrilateral head; he eternally eyes Vega.

FRIDAY, JULY 31

■ The waxing gibbous Moon shines just over the Sagittarius Teapot this evening, as shown below. Covering the Moon with your finger will make the Teapot stars easier to see, unless your evening sky is too bright with summer haze.

On August 1st, the almost-full Moon shines with just-past-full Jupiter and Saturn. The Moon and planets appear full when they’re at opposition: opposite the Sun as seen from Earth. But planets move westward with respect to your landscape as the year revolves, while the Moon moves east from night to night. So, when the Moon and an outer planet appear near each other in the sky, one is on its way to its opposition and the other is past its opposition.

Another way to put this: Planets near a waxing Moon are always past opposition. Planets near a waning Moon are always on their way to opposition.

SATURDAY, AUGUST 1

■ The nearly full Moon this evening forms a triangle with Jupiter and Saturn, more or less as shown above. These sky scenes are always drawn exact for a viewer at latitude 40° north, longitude 90° west: near the middle of North America. They’re close enough for the rest of the continent, but don’t expect perfection if you’re in Boston or Florida or California.

■ Today is Lammas Day or Lughnasadh, one of the four traditional “cross-quarter” days midway between the solstices and the equinoxes. Sort of. Over the centuries since this tradition took root in Europe, the calendar drifted with respect to Earth’s position in its orbit. So in 2020, the midpoint between the June solstice and the September equinox actually falls on August 5th, at 1:08 p.m. Eastern Daylight Time (17:08 UT).

That minute is the exact center-balance of astronomical summer: the very height of the circle of the year.

This Week’s Planet Roundup

Mercury is having a fairly good dawn apparition. Look low in the east-northeast as dawn brightens. Mercury remains at about the same height from morning to morning, while brightening from magnitude –0.2 on July 25th to –0.9 on August 1st: twice as bright! Mercury brightens because it is swinging around the Sun and showing us more of its sunlit side.

Venus (magnitude –4.6, in Taurus) rises in deep darkness about 1½ hour before the very beginning of dawn. As dawn gets under way, Venus blazes brightly in the east.

Look for Aldebaran, 160 times fainter at magnitude +0.9, moving farther away to Venus’s upper right each morning. The Pleiades glimmer more than a fist at arm’s length above Aldebaran. The bright star nearly three fists to Venus’s upper left is Capella.

In a telescope Venus is a thick crescent, shrinking this week from 30 to 28 arcseconds tall and waxing from 39% to 42% sunlit.

Mars rises due east around 11 or midnight daylight saving time, a bright yellow-orange firespark (magnitude –1.0) between Pisces and Cetus. Watch for it to rise below the Great Square of Pegasus. (On the night of July 28th, the Great Square’s vertical diagonal points down to Mars precisely.) By dawn Mars shines grandly high and bright in the south-southeast: a far-off bonfire in the heavens.

In a telescope this week Mars grows from 13.5 to 14 arcseconds in apparent diameter, which is as big as it appears at some oppositions! But we’re still speeding toward it along Earth’s faster orbit around the Sun. Around this year’s opposition of Mars in early October, it will appear 22.6 arcseconds wide.

Mars is still very gibbous, 86% sunlit. Look for its white South Polar cap and for subtler dark surface markings. To get a map of the side of Mars facing you at the date and time you’ll observe, use our Mars Profiler. The map there is rectangular; remember to mentally wrap it onto the side of a globe. (Features on the map’s edges become very foreshortened.)

An extraordinarily high-res image of Mars, taken July 17th by Enrico Enzmann and Damian Peach when Mars was 12.9 arcseconds in apparent diameter. South is up. Peach says this is “the first in a collaboration with friend and astronomer Rico Enzmann. Mars this morning is looking very hazy with airborne dust.” They used a 76cm (30-inch) Ritchey-Chretien telescope with a Canon ME20 camera to acquire video frames for stacking.

The darkest horizontal streak near center is Sinus Sabaeus, ending on its right (“following”) end with two-pronged Sinus Meridiani. Upper right of that is Margaritifer Sinus.

Jupiter and Saturn (magnitudes –2.7 and +0.1, respectively) were recently at opposition: Jupiter on the night of July 13th, Saturn on the 20th. They loom in the southeast in twilight and pass highest in the south around midnight daylight-saving time. Jupiter is brightest; Saturn is 7° to its lower left or left. Farther to Jupiter’s right is the Sagittarius Teapot.

Keep up with the telescopic interplay of Jupiter with its moons and their shadows, and find all the transit times of Jupiter’s Great Red Spot, in the Celestial Calendar section of the current month’s Sky & Telescope.

Jupiter at opposition, July 14, 2020Jupiter on July 14th, imaged by Christopher Go in the Philippines. South is up. The Great Red Spot has barely come around the following (celestial east) limb. Blue festoons in the Equatorial Zone have merged to form a great blue patch. Writes Go, “The North Equatorial Belt shows chaotic upheaval; complex rifts and outbreaks.” The South Equatorial Belt is quieter, though a bright line of cloud along its center divides it in two. Saturn on July 9th as imaged by Christopher Go. South is up. The ring tilt has lessened enough that a bit of the globe now peeks up from behind the rings’ south edge. On the globe, a small white storm at latitude 63° north, and a slight dent in the edge of the North Equatorial Belt almost dead center, have been brought out by boosting the image’s brightness contrast and color contrast, and by edge enhancement. This processing has added artifacts around sharp edges in the rings.

Uranus (magnitude 5.8, in Aries) is high in the east before dawn, far to the celestial east of Mars.

Neptune (magnitude 7.8, in Aquarius) is high in the south before dawn, far west of Mars.

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 known as UT, UTC, GMT, or Z time) minus 4 hours.

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.

Jumbo Pocket Sky Atlas coverThe Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown here is the Jumbo Edition for easier reading outdoors at 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) or 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 Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger (and illustrated) 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.”

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.

“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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