This Week’s Sky at a Glance, Sept. 24 – Oct. 2

Nova Cassiopeiae 2021 carries on, fluctuating unpredictably because it stays in binocular view six months after its March explosion. As of September twenty first it was again as much as magnitude 6.7, greater than twice as vibrant as its unique March eruption from its Fifteenth-magnitude baseline. Charts and comparison stars.


■ Bright Jupiter and fainter Saturn proceed to dominate the southern night sky, 16° aside. All week Jupiter shines simply above or higher proper of Third-magnitude Delta Capricorni, Deneb Algedi (the identify means “Tail of the Young Goat”). The scene is proven under for late twilight this night.

Farther to the higher proper of Saturn, search for Alpha and Beta Capricorni. Both are binocular double stars. Alpha is a huge pair of yellow-orange giants that the smallest binoculars simply resolve; so does our chart under. The parts of Beta are half as far aside, way more unequal, and oriented roughly the identical way because the Alpha pair.

As the stars come out this week, search for Third-magnitude Delta Capricorni just under or decrease left of Jupiter. Tonight they’re 1.5° aside, about a finger’s width at arm’s size. Jupiter is 175 instances brighter! How early (or extra probably, late) in twilight are you able to first make out Delta Cap?

Delta Cap is an attention-grabbing star: a magnetic white subgiant, spectral class A7m, 9 instances brighter than the Sun and intently orbited by a small, dim orange dwarf nearly precisely as soon as a day. The dwarf passes in entrance of the intense star each orbit from our standpoint, dimming it by 0.24 magnitude. That’s theoretically discernable by eye however with out near-match comparability stars close by, good luck. The system is simply 39 light-years away.

■ Jupiter’s Great Red Spot ought to cross Jupiter’s central meridian round 9:04 p.m. Eastern Daylight Time. For full timetables of the Red Spot’s transits in addition to the doings of Jupiter’s moons and their shadows, see the Celestial Calendar part of Sky & Telescope journal.


■ Cygnus the Swan floats nearly straight overhead these evenings. Its brightest stars type the large Northern Cross. When you face southwest and crane your head way, way up, the cross seems to face upright. It’s about two fists at arm’s size tall, with Deneb as its prime. Or to place it one other way, whenever you face that course the Swan seems to be diving straight down.

The waning gibbous Moon would not rise now till about an hour after darkish. So take this chance to search for the Milky Way operating straight up from the west-southwest horizon, alongside the spine of Aquila and simply to the correct of vibrant Altair excessive within the south; then alongside the shaft of the Northern Cross overhead, and straight down by Cassiopeia and northern Perseus to the east-northeast horizon.


■ Bright Arcturus, pale yellow-orange, shines ever decrease within the west-northwest at dusk. The slim kite form of its constellation, Bootes, extends two fists at arm’s size to Arcturus’s higher proper. Arcturus is the place the kite’s downward-hanging tail is tied on.

To the correct of the highest of the kite, the Big Dipper is popping extra degree.

And that is the time of year when, in the course of the night, the dim Little Dipper “dumps water” into the bowl of the Big Dipper way down under. The Big Dipper will dump it again within the evenings of spring.

■ Tonight Jupiter’s Great Red Spot ought to cross the planet’s central meridian round 10:42 p.m. EDT (7:42 p.m. Pacific). It stays in good view for about an hour earlier than and after that point.


■ Arcturus shines within the west in late twilight these evenings. Capella, equally vibrant, is simply rising within the north-northeast (relying in your latitude; the farther north you’re the larger it is going to be). They’re each magnitude 0.

Later within the night, Arcturus and Capella shine at equal heights of their respective compass instructions. When will this occur? That depends upon each your latitude and longitude.

When it does, flip round and look low within the south-southeast. There will probably be 1st-magnitude Fomalhaut at the about identical peak too — precisely so for those who’re at latitude 43° north (concerning the latitude of Boston, Buffalo, Milwaukee, Boise, Eugene). Seen from south of that latitude, Fomalhaut will seem larger than Capella and Arcturus are. Seen from north of there, it is going to be decrease.


■ Last-quarter Moon tonight (precise at 9:57 p.m. Eastern Daylight Time). The Moon rises round 11 or midnight in Gemini, down under Capella and the remainder of Auriga.

An hour later look off to the Moon’s proper, and there is Orion stepping up over the japanese horizon (for viewers at mid-northern latitudes).


■ The starry W of Cassiopeia stands excessive within the northeast after darkish. The right-hand facet of the W (the brightest facet) is tilted up.

Look at the second section of the W counting down from the highest. Notice the dim naked-eye stars alongside that section (not counting its two ends). The brightest of those, on the correct, is Eta Cassiopeiae, magnitude 3.4. This is a remarkably Sun-like star simply 19 light-years away, and it has a orange-dwarf companion, magnitude 7.3, separation 13 arcseconds a pretty binary in a telescope.

Left of it, and fainter, is a naked-eye pair in a darkish sky: Upsilon1 and Upsilon2 Cassiopeiae, a good 0.3° aside. They’re yellow-orange giants unrelated to one another, 200 and 400 light-years distant from us. Upsilon2 is barely the brighter of the pair. It’s additionally the nearer one.

■ Night owl? Look east any time from 1 or 2 a.m. to early daybreak Thursday morning, and you will find the waning Moon close to Pollux in Gemini. Above Pollux is Castor.


■ The huge asteroid 2 Pallas, nearly three weeks previous opposition, stands excessive within the southeast by 9 or 10 p.m. It’s nonetheless in small-telescope attain at magnitude 8.4. This week Pallas is 8° or 9° higher proper of Neptune, magnitude 8.7, which is also previous opposition. Read about each and hunt them down utilizing the finder charts in Asteroid Pallas Makes a Point in Pisces.


■ Vega is the brightest star simply west of the zenith after darkish. Face west and look to Vega’s proper by 14° (practically a fist and a half at arm’s size) for Eltanin, the nostril of Draco the Dragon. The remainder of Draco’s fainter, lozenge-shaped head is a little farther behind. Draco all the time eyes Vega as they wheel across the sky.

The fundamental stars of Vega’s personal constellation, Lyra — faint by comparability — lengthen to its left (by 7°).

■ Before and through early daybreak Saturday morning October 2nd, look under the crescent Moon by about a fist at arm’s size for Regulus, forefoot of Leo already making his early-apparition look, as proven under.

Leo publicizes spring when it is on the rise within the early night sky. But Leo’s arrival within the east at the start of daybreak? That publicizes October.


■ During night, look simply above the northeast horizon — far under excessive Cassiopeia — for vibrant Capella on the rise. How quickly Capella rises, and the way excessive you may discover it, depends upon your latitude. The farther north you’re, the earlier and better.

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

■ Before and through early daybreak Sunday morning October Third, the waning crescent Moon varieties a flat, nearly isosceles triangle with Regulus and Algieba (Gamma Leonis) to Regulus’s left or higher left, as proven above (for North America).



This Week’s Planet Roundup

Mercury is hidden deep within the glare of the Sun.

Venus, good at magnitude –4.2, shines low within the southwest throughout twilight. And it nonetheless units round twilight’s finish.

Jupiter and Saturn proceed to shine within the southeast to south throughout night. They’re magnitudes –2.7 and +0.5, respectively, 16° aside on reverse sides of dim Capricornus.

During twilight vibrant Jupiter, on the left, is barely the decrease of the 2. They degree out quickly after darkish, and later they tilt the opposite way, with Saturn now the decrease one. Saturn units round 2 a.m. daylight-saving time, adopted down by Jupiter about an hour later.

In the night search for 1st-magnitude Fomalhaut 23° (two fists) decrease left of Jupiter. And lower than 2° under or decrease left of Jupiter is Third-magnitude Delta Capricorni, described within the caption above.

Also, see Amateurs Spot New Impact Flash at Jupiter. With movies of it taken by two novice Jupiter-impact screens.

Uranus (magnitude 5.7, in southern Aries) climbs excessive within the east by midnight.

Neptune (magnitude 7.8, at the Aquarius-Pisces border) is excessive within the southeast by 9 or 10 p.m.

All descriptions that relate to your horizon — together with the phrases up, down, proper, and left — are written for the world’s mid-northern latitudes. Descriptions that additionally rely on longitude (primarily Moon positions) are for North America.

Eastern Daylight Time, EDT, is Universal Time minus 4 hours. Universal Time is also referred to as UT, UTC, GMT, or Z time. To change into extra skilled about time methods than 99% of the individuals you may ever meet, see our compact article Time and the Amateur Astronomer.

Want to change into a higher astronomer? Learn your way across the constellations. They’re the important thing to finding every part fainter and deeper to hunt with binoculars or a telescope.

This is an out of doors nature interest. For an easy-to-use constellation information masking the entire night sky, use the large month-to-month map within the heart of every subject of Sky & Telescope, the important journal of astronomy.

Once you get a telescope, to place it to good use you may want a detailed, large-scale sky atlas (set of charts). The primary commonplace is the Pocket Sky Atlas (in both the original or Jumbo Edition), which exhibits stars to magnitude 7.6.

Pocket Sky Atlas cover, Jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and lots of of telescopic galaxies, star clusters, and nebulae amongst them. Shown right here is the Jumbo Edition, which is in laborious covers and enlarged for simpler studying open air by red flashlight. Sample charts. More about the current editions.

Next up is the bigger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; practically 3 times as many. The subsequent up, as soon as you recognize your way round, are the even bigger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And make sure you learn How to Use a Star Chart at the Telescope.

You’ll additionally need a good deep-sky guidebook, akin to the large Night Sky Observer’s Guide by Kepple and Sanner.

Can a computerized telescope exchange charts? Not for learners, I do not suppose, and never on mounts and tripods which might be lower than top-quality mechanically, which means heavy and costly. And as Terence Dickinson and Alan Dyer say of 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 below the night sky together with your
earbuds in place, take heed to Kelly Beatty’s month-to-month
(*24*) 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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