This Week’s Sky at a Glance, October 1 – 9 – Sky & Telescope

Nova Cassiopeiae 2021 was back down to magnitude 7.8 as of September 28th, and it may be reddening again. Charts and comparison stars.


■ Vega is the brightest star just west of the zenith after dark this week. Face west, crane your head up, and look to Vega’s right by 14° (nearly a fist and a half at arm’s length) for 2nd-magnitude Eltanin, the nose of Draco the Dragon. The rest of Draco’s fainter, lozenge-shaped head is a little farther behind. Draco always eyes Vega as they wheel around the sky.

The main stars of Vega’s own constellation, Lyra — faint by comparison — extend to Vega’s left by half as far as the distance from Vega to Eltanin.

■ Bright Jupiter and fainter Saturn continue to dominate the southeast to south these evenings, 16° apart.

Look upper right of Saturn, by 6° or 8°, for 3rd-magnitude Alpha and Beta Capricorni. Both are binocular double stars. Alpha, the upper one, is a wide pair of yellow-orange giants that the smallest binoculars easily resolve. The components of Beta are rather harder; they’re half as far apart and much more unequal. They’re oriented roughly the same way as the Alpha pair. (For more on these stars and their surroundings, see “Capricious Capricornus” in the the October Sky & Telescope, page 45.)

■ Tonight Jupiter’s Great Red Spot should cross Jupiter’s central meridian around 9:54 p.m. EDT. The Red Spot remains closer to the central meridian than to the planet’s limb for 50 minutes before and after it transits.

■ Before and during early dawn Saturday morning October 2nd, look below the crescent Moon by about a fist at arm’s length for Regulus. It’s the forefoot of Leo, who is already in his early-apparition dawn arrival as shown below.

Leo announces spring when he’s on the rise in the early-evening sky. But Leo’s rise in the east at the beginning of dawn? That announces October.


■ During evening, look just above the northeast horizon — far below high Cassiopeia — for bright Capella on the rise. How soon Capella rises, and how high you’ll find it, depend on your latitude. The farther north you are, the sooner and higher.

■ Vega is the brightest star very high in the west, while Arcturus is getting low in the west-northwest. The brightest star in the vast expanse between them, about a third of the way from Arcturus up toward Vega, is Alphecca, magnitude 2.2 — the crown jewel of dim Corona Borealis. Alphecca is a 17-day eclipsing binary, but (like most variable stars!) its brightness dips are too slight for the eye to see reliably.

■ Before and during early dawn Sunday morning October 3rd, the waning crescent Moon forms a flat, almost isosceles triangle with Regulus and Algieba (Gamma Leonis) to Regulus’s left or upper left, as shown above (for North America).


■ Globular clusters are at their most abundant on summer evenings. In this first week of October, with moonlight gone from the evening sky, set up your telescope to look in on four that Josh Urban calls The Last Wildflowers: Globular Clusters Greet Autumn. There’s “Sagittifolia,” the Arrowhead Flower M71 in Sagitta; “Queen Anne’s Lace,” M15 sneezed from the nose of Pegasus; “Watercress by the Stream,” M2 in Aquarius a little farther south; and “Seaflower of the Deep,” M30 in Capricornus down below Jupiter.


■ Jupiter’s moon Io enters onto the planet’s face at 9:19 p.m. EDT, followed by its tiny black shadow one hour later. Io leaves Jupiter’s western side at 11:36 p.m. EDT, again followed by its shadow an hour later. See the “Action at Jupiter” timetables for the whole month, good worldwide, in the October Sky & Telescope, pages 50-51.


■ Arcturus shines in the west in late twilight these evenings. Capella, equally bright, is coming up in the north-northeast (depending on your latitude; the farther north you are the higher it will be). They’re both magnitude 0.

Later in the evening, Arcturus and Capella shine at equal heights in their respective compass directions. When will this happen? That depends on both your latitude and longitude.

When it does, turn around and look low in the south-southeast. There will be 1st-magnitude Fomalhaut at the about same height too — exactly so if you’re at latitude 43° north (about the latitude of Boston, Buffalo, Milwaukee, Boise, Eugene). Seen from south of that latitude, Fomalhaut will appear higher than Capella and Arcturus are. Seen from north of there, it will be lower.


■ Now that it’s October, Deneb has replaced Vega as the zenith star of early dark evening (for skywatchers at mid-northern latitudes). Accordingly, Capricornus has replaced Sagittarius as the zodiacal constellation low in the south. This year, of course, Capricornus is overwhelmed by its two bright temporary residents: Jupiter and Saturn.

■ New Moon (exact at 7:05 a.m. EDT).


■ The Great Square of Pegasus balances on its corner high in the east through much of the evening. Away from the Great Square’s left corner extends the main line of Andromeda, three 2nd-magnitude stars about as bright as those of the Square and spaced similarly far apart. (The three include the Square’s corner.) This whole dipper-shaped pattern was named the Andromegasus Dipper by the late Sky & Telescope columnist George Lovi joining the Big and Little Dippers, the Milk Dipper of Sagittarius (nowadays usually subsumed into the Teapot), and the tiny dipper pattern of the Pleiades.


■ Spot Venus low in the southwest as early in twilight as you can. Then look lower right of it by some 12° (about a fist at arm’s length) for the thin crescent Moon. Binoculars help.

If you find the ideal time of compromise between the sky still being too bright and the Moon sinking too low, you should get a fine view of earthshine dimly lighting the Moon’s nightlands inside the crescent. And the Moon is at perigee today, so it will appear a trace larger than average: a supercrescent moon.


■ Now the Moon shines only about 3° above Venus in twilight (for North America), just while Venus is passing ¾° lower left of 2nd-magnitude Delta Scorpii, as shown below. Bring binoculars.

Crescent Moon with Venus in the head of Scorpius, Oct. 9, 2021
Set your calendar on the 9th to catch the Moon in conjunction with Venus while Venus is in closer conjunction with Delta Scorpii. Bring your binoculars.



This Week’s Planet Roundup

Mercury and Mars are out of sight in conjunction with the Sun.

Venus, brilliant at magnitude –4.3, shines low in southwest during twilight, in Libra. It sets a little after twilight’s end.

Look to Venus’s left as twilight deepens for orange Antares in Scorpius. Between them for most of the week is Delta Scorpii, not too much fainter than Antares. Binoculars will help you pick out both stars in the deepening blue.

Watch Venus close in on Delta Sco day by day. They pass just ¾° apart on October 9th, with the thin crescent Moon right close by as shown above. A week later on the 16th, Venus will pass 1½° above Antares.

Jupiter and Saturn continue to shine in the southeast to south during evening, 16° apart on opposite sides of dim Capricornus. Jupiter is the eye-grabber at magnitude –2.7. Saturn, to its right, is a twentieth as bright at mag +0.5.

By the end of twilight they sit equally high in the south-southeast. As evening progresses watch them tilt to the right, with Saturn the lower one. Saturn sets around 1 or 2 a.m. daylight-saving time, followed by Jupiter about an hour later.

After dark look 23° (two fists at arm’s length) lower left of Jupiter for 1st-magnitude Fomalhaut. About 2° lower left of Jupiter, spot 3rd-magnitude Delta Capricorni.

Here’s a beginner’s telescopic guide to Jupiter.

Uranus (magnitude 5.7, in southern Aries) climbs high in the east by 11 or midnight.

Neptune (magnitude 7.8, at the Aquarius-Pisces border) is already well up in the in the southeast by the time darkness is complete.

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 a Star Chart with a Telescope.

You’ll also want a good deep-sky guidebook, such as the big 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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