This Week’s Sky at a Glance, September 17 – 25

Nova Cas will not stop. Last week Nova Cassiopeiae 2021 jumped up but once more, to magnitude 6.6 its seventh bump-up between fades since its unique explosion to magazine 7.7 final March. As of September sixteenth it was again right down to 7.5. Charts and comparison stars.


Watch the Moon step eastward under Jupiter on its way to full on the twentieth.

FRIDAY, SEPTEMBER 17

■ The gibbous Moon hangs decrease proper of brilliant Jupiter at nightfall this night, as proven above. To their proper, Saturn glows dimmer within the background.

Later within the night time, because the sky turns, The Moon will turn out to be instantly under Jupiter and Saturn will flip to be decrease than each of them. That’s how you will discover them oriented round midnight (daylight saving time).

SATURDAY, SEPTEMBER 18

■ You can see within the stars that the season is altering: We’ve reached the time of year when, simply after dusk, cold-weather Cassiopeia has already climbed a little greater within the northeast than the warm-weather Big Dipper has sunk within the northwest. Cassiopeia bedecks the excessive northern sky in early night throughout the fall-winter half of the year. The Big Dipper takes over for the milder evenings of spring and summer time.

Almost halfway between them stands Polaris. It’s at the moment a little above the midpoint between the 2.

SUNDAY, SEPTEMBER 19

■ The brilliant moon this night kinds a lengthy, gently curving arc with Jupiter after which Saturn to its higher proper. That’s their order not solely alongside the arc however by way of brightness, and by way of distance. The Moon is 1.3 light-seconds from Earth, Jupiter is at the moment 36 light-minutes away, and Saturn is 77 light-minutes away.

■ Sign of the altering season: The closing days of summer time (the autumn equinox comes on Wednesday the twenty second) all the time discover the Sagittarius Teapot shifting west of south throughout night and tipping more and more far over to the appropriate, as if pouring out the final of summer time by means of its spout.

MONDAY, SEPTEMBER 20

■ Full Moon (actual at 7:55 p.m. Eastern Daylight Time). Look a couple of fists to its higher left for the Great Square of Pegasus, emblem of fall, ever greater now. By midnight, when the Moon shines almost at its highest, the Great Square stands above it.

TUESDAY, SEPTEMBER 21

■ Jupiter’s moon Europa reappears out of eclipse from Jupiter’s shadow round 9:58 p.m. EDT. A small telescope will present it progressively swelling into view simply off Jupiter’s japanese limb. Then the Great Red Spot ought to cross Jupiter’s central meridian round 11:34 p.m. EDT (8:34 p.m. PDT).

For timetables of all such goings-on at Jupiter this month, see the September Sky & Telescope, pages 50-51.

WEDNESDAY, SEPTEMBER 22

■ Fall begins within the Northern Hemisphere, and spring within the Southern Hemisphere, at the equinox: 3:21 p.m. Eastern Daylight Time (19:21 UT). This is when the Sun crosses the equator — each Earth’s equator and, equivalently, the celestial equator —heading south for the season.

■ Coincidentally, as if to mark this transition each year, Deneb is taking on from brighter Vega because the zenith star after dusk (for skywatchers at mid-northern latitudes).

THURSDAY, SEPTEMBER 23

■ The large asteroid 2 Pallas, a little previous opposition, stands excessive within the southeast by 10 p.m., in small-telescope attain at magnitude 8.4. This week it is solely 7° or 8° higher proper of Neptune, magnitude 8.7. Which can also be, essentially, a little previous opposition. Read about each and hunt them down utilizing the finder charts in Asteroid Pallas Makes a Point in Pisces.

FRIDAY, SEPTEMBER 24

■ Bright Arcturus, pale yellow-orange, shines ever decrease within the west-northwest after darkish. The slender 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 appropriate of the highest of the kite, the Big Dipper is popping extra degree.

And that is the time of year when, throughout 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.

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

It’s an fascinating star: a magnetic white subgiant, spectral class A7m, 9 occasions brighter than the Sun and carefully orbited by a small, dim orange dwarf nearly precisely as soon as a day. The dwarf passes in entrance of the brilliant star each orbit from our perspective, dimming it by 0.24 magnitude. That’s theoretically discernable by eye however with out a near-match comparability star proper close by, good luck. The system is just 39 light-years away.

SATURDAY, SEPTEMBER 25

■ Cygnus the Swan floats nearly straight overhead these evenings. Its brightest stars kind the massive 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, if you face that course the Swan seems to be diving straight down (one thing actual swans by no means do).

The Moon will not rise now till about an hour after darkish. So take this chance to search for the Milky Way working straight up from the west-southwest horizon, alongside the spine of Aquila and to the excellent of brilliant Altair excessive within the south, alongside the shaft of the Northern Cross overhead, and straight down by means of Cassiopeia and northern Perseus to the east-northeast horizon.

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This Week’s Planet Roundup

Mercury is hidden deep within the glow of sundown.

Venus, good at magnitude –4.1, shines low within the west-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 –2.8 and +0.4, respectively, 16° aside on reverse sides of dim Capricornus.

During twilight brilliant Jupiter, on the left, is barely the decrease of the 2. They degree out not lengthy after darkish, and later they tilt the opposite way, with Saturn now the decrease one. Saturn units round 2 or 3 a.m. daylight-saving time, adopted down by Jupiter about an hour later.

In the night search for 1st-magnitude Fomalhaut some 22° (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 two movies of it taken by diligent, tireless beginner 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 often known as UT, UTC, GMT, or Z time. To turn out to be extra knowledgeable about time methods than 99% of the individuals you will ever meet, see our compact article Time and the Amateur Astronomer.


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

This is an outside nature pastime. For an easy-to-use constellation information protecting the entire night sky, use the massive month-to-month map within the middle of every difficulty of Sky & Telescope, the important journal of astronomy.

Once you get a telescope, to place it to good use you will 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 tons 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. (*17*).

Next up is the bigger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; almost 3 times as many. The subsequent up, as soon as you recognize your way round, are the even bigger (*25*) atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And you’ll want to learn How to Use a Star Chart at the Telescope.

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

Can a computerized telescope change charts? Not for inexperienced persons, I do not assume, and never on mounts and tripods which can be lower than top-quality mechanically, that 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 beneath the night sky along with your
earbuds in place, hearken to Kelly Beatty’s month-to-month
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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