This Week’s Sky at a Glance, July 2 – 10 – Sky & Telescope

Nova Cas gets jumpy. It’s been 3½ months since Nova Cassiopeiae 2021 erupted to magnitude 7.7 in mid-March. It has stayed roughly that bright ever since (making it officially a “slow nova”) except for briefly swelling to 5.3, faint naked-eye visibility, for a week in May. It’s been wavering since then and faster now. As of July 1 it was about 7.4, having dropped from 6.7 (a halving of brightness) in just the previous two days.

The nova is fairly well up in the north-northeast after dark depending on your latitude. It climbs higher later in the night. See Bob King’s new update: Noctilucent Cloud Show, a Mercurial Nova, and More, with charts and comparison stars for the nova.


■ Venus continues to shine low in the west-northwest during twilight. Mars, only 1/175 as bright, is now just 6° to its upper left as shown below. They set before twilight’s end.

Watch the two planets close in on each other day by day. They’ll be in conjunction, ½° apart, on July 12th and 13th.

Venus and Mars point a line to Regulus in the western twilight. The stars of the Beehive, behind Venus this evening, are way too faint to be plotted. But they’re there. . . .
Mercury and Aldebaran low at dawn, July 3, 2021.
Mercury, low in the dawn, will double in brightness this week. Can you spot it yet? The visibility of faint points in bright twilight is exaggerated here!


■ Low in the northwest or north at the end of these long summer twilights, would you recognize noctilucent clouds if you saw them? They’re the most astronomical of all cloud types, what with their extreme altitude and their formation on, in part, meteoric dust particles. And they’re fairly rare — though they’ve become more common in recent years as the climate and the atmosphere change, particularly the atmosphere’s methane content. See Bob King’s Noctilucent Cloud Show, a Mercurial Nova, and More.

■ After dark, the Summer Triangle holds sway on the eastern side of the sky. Its top star is Vega, the brightest. The brightest star to Vega’s lower left is Deneb. Farther to Vega’s lower right is Altair. The Milky Way (if you have a dark enough sky) runs across inside the Triangle’s lower edge.

■ As evening grows late and even Altair rises high, look left of Altair, by hardly more than a fist, for the compact little constellation Delphinus, the Dolphin.

Did you get it? Then try for even fainter, smaller Sagitta, the Arrow. It’s to Altair’s upper left just a little closer. The Arrow points toward lower left, past the nose of Delphinus.


■ Star colors are mostly subtle, and different people have an easier or harder time seeing them. To me, the tints of bright stars show a little better on a late-twilight sky background than in a fully dark sky.

For instance, the two brightest stars of summer are Vega, high in the east in late twilight, and Arcturus, even higher in the southwest. Vega is white with just a touch of icy blue. Arcturus is a yellow-orange giant. Do their colors stand out a little better for you in late twilight than in dark night?

Binoculars, of course, always make star colors much easier.


■ As dawn begins on Monday morning the 6th, the waning crescent Moon hangs between the Pleiades above it and Aldebaran below it, as shown below.

The waning crescent Moon poses above Aldebaran and Mercury on the mornings of, respectively, July 6th and 7th.


■ Look for Mercury, low but continuing to brighten, below the thin Moon as dawn brightens on Wednesday morning the 7th as shown above.


■ Antares and the rest of starry Scorpius are at their highest in the south just after these long July twilights finally fade away.

The head of Scorpius is the near-vertical row of three stars upper right of Antares. Three fine doubles stars await you here. The top star of the row is Beta Scorpii or Graffias, a fine binary 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, diagonal from upper right to lower left. 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 this is a telescopic triple. High power in good seeing reveals Nu’s brighter component itself to be a close double, separation 2 arcseconds, magnitudes 4.0 and 5.3, aligned almost north-south.

And more: In the same binocular field with Antares, or nearly so, are two very different globular star clusters for binoculars and telescopes. M4 is a big, dim fuzzy relatively nearby for a globular. M80 is fainter and much more compact; in fact it can be hard to distinguish in binoculars from an 8th-magnitude star. It’s a bigger and denser cluster than M4 but more than four times as far away. Use the chart for them with Matt Wedel’s Binocular Highlight column in the July Sky & Telescope, page 43.


■ With the advance of summer, the Sagittarius Teapot, in the south-southeast lower left of Scorpius after dark, 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.

■ Jupiter’s Great Red Spot should be on the planet’s central meridian around 2:45 a.m. Eastern Daylight Time. Around that time Callisto and Ganymede are both at their farthest east of the planet, while Io and Europa are close in to Jupiter’s west. There, Europa disappears into eclipse by Jupiter’s shadow around 3:39 a.m. EDT.

For timetables of many more the phenomena among Jupiter and its satellites this month, good worldwide, see the July Sky & Telescope, pages 50-51.


■ As twilight comes to its end, you’ll now 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).

About a third of the way from Arcturus to Vega is the faint semicircle of Corona Borealis, the Northern Crown, with its one modestly bright crown jewel, Alphecca or Gemma, on its front.

Nearly two thirds of the way from Arcturus to Vega is the Keystone of Hercules.

For more see Fred Schaaf’s “The Path from Arcturus to Vega” in the July Sky & Telescope, page 45.

■ New Moon (exact at 9:17 p.m. EDT).


■ If you have a dark enough sky on these moonless nights, the Milky Way now forms a magnificent arch high across the whole eastern sky. It runs all the way from below Cassiopeia in the north-northeast, up and across Cygnus and the Summer Triangle in the east, and down past the spout of the Sagittarius Teapot in the south.



This Week’s Planet Roundup

Mercury glimmers very low in the east-northeast as dawn grows bright. Mercury remains low all week but brightens from magnitude +0.8 to 0.0. Binoculars or a wide-field telescope will help. Don’t confuse Mercury with faster-twinkling Aldebaran increasingly far to its upper right; see the illustration for July 3 above.

Venus (magnitude –3.8) shines low in the west-northwest during twilight. Tiny Mars, nearly 200 times fainter at magnitude +1.8, is closing in on Venus from the upper left. They’re separated by 6° on July 2nd, closing to 2° by the 9th. They’ll be in conjunction, ½° apart, on July 12th and 13th. Both planets set before twilight ends.

Saturn (in Capricornus) and brighter Jupiter (in Aquarius) show up by late evening. Saturn rises around the end of twilight. Jupiter comes up one hour later, to Saturn’s lower left. They’re up in fine view after midnight, and they’re highest in the south at their telescopic best in the hour before dawn begins. See “Saturnian Challenges” in the July Sky & Telescope, page 52.

Jupiter dominates at magnitude –2.6. Saturn, 20° to Jupiter’s west (right), is a more modest +0.4. They’ll reach opposition in August.

Before dawn, look 20° below or lower left of Jupiter for Fomalhaut. It forms an isosceles right triangle with Jupiter and Saturn. Jupiter is at the (almost) right angle.

Two dark red barges were near Jupiter’s central meridian when Christopher Go took this image on June 15th (at 19:03 UT, when the System II longitude of the central meridian was 79°). The rest of the North Equatorial Belt has faded greatly, except for a very dark red line along its southern edge. (South is up.) Meanwhile, the normally bright Equatorial Zone mostly remains a pale, almost belt-like tan color.

Uranus (magnitude 5.8, in Aries) is fairly low in the east before dawn begins.

Neptune (magnitude 7.9, in Aquarius 21° east of Jupiter) is well up in the southeast before dawn begins.

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 minus 4 hours. Universal Time is also known as UT, UTC, GMT, or Z time. To become more expert about time systems than 99% of the people you’ll ever meet, see our compact article Time and the Amateur Astronomer.

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.

Pocket Sky Atlas cover, Jumbo edition
The 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, which is in hard covers and enlarged for easier reading outdoors by red flashlight. Sample charts. More about the current editions.

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 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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