#astronomy This Week’s Sky at a Look, September 17 – 25 – Sky & Telescope

September 19, 2021 - Comment

Nova Cas will not stop. Final week Nova Cassiopeiae 2021 jumped up but once more, to magnitude 6.6 — its seventh bump-up between fades since its authentic explosion to magazine 7.7 final March. As of September 16th it was again right down to 7.5. Charts and comparability stars. Watch the Moon step eastward under Jupiter

Nova Cas will not stop. Final week Nova Cassiopeiae 2021 jumped up but once more, to magnitude 6.6 — its seventh bump-up between fades since its authentic explosion to magazine 7.7 final March. As of September 16th it was again right down to 7.5. Charts and comparability stars.

Watch the Moon step eastward under Jupiter on its strategy to full on the 20th.


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

Later within the evening, because the sky turns, The Moon will grow to be immediately under Jupiter and Saturn will flip to be decrease than each of them. That is how you may discover them oriented round midnight (daylight saving time).


■ You possibly can see within the stars that the season is altering: We have reached the time of 12 months when, simply after dusk, cold-weather Cassiopeia has already climbed just a little larger within the northeast than the warm-weather Huge Dipper has sunk within the northwest. Cassiopeia bedecks the excessive northern sky in early night throughout the fall-winter half of the 12 months. The Huge Dipper takes over for the milder evenings of spring and summer season.

Virtually halfway between them stands Polaris. It is presently just a little above the midpoint between the 2.


■ The brilliant moon this night kinds a protracted, gently curving arc with Jupiter after which Saturn to its higher proper. That is their order not solely alongside the arc however by way of brightness, and by way of distance. The Moon is 1.three light-seconds from Earth, Jupiter is presently 36 light-minutes away, and Saturn is 77 light-minutes away.

■ Signal of the altering season: The closing days of summer season (the autumn equinox comes on Wednesday the 22nd) 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 season by its spout.


■ Full Moon (precise at 7:55 p.m. Japanese Daylight Time). Look a few fists to its higher left for the Nice Sq. of Pegasus, emblem of fall, ever larger now. By midnight, when the Moon shines practically at its highest, the Nice Sq. stands above it.


■ 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 jap limb. Then the Nice Pink Spot ought to cross Jupiter’s central meridian round 11:34 p.m. EDT (eight:34 p.m. PDT).

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


■ Fall begins within the Northern Hemisphere, and spring within the Southern Hemisphere, on the equinox: three:21 p.m. Japanese Daylight Time (19:21 UT). That is when the Solar crosses the equator — each Earth’s equator and, equivalently, the celestial equator —heading south for the season.

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


■ The massive asteroid 2 Pallas, just a little previous opposition, stands excessive within the southeast by 10 p.m., in small-telescope attain at magnitude eight.four. This week it is solely 7° or eight° higher proper of Neptune, magnitude eight.7. Which can be, essentially, just a little previous opposition. Examine each and hunt them down utilizing the finder charts in Asteroid Pallas Makes a Level in Pisces.


■ Brilliant Arcturus, pale yellow-orange, shines ever decrease within the west-northwest after darkish. 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 appropriate of the highest of the kite, the Huge Dipper is popping extra stage.

And that is the time of 12 months when, throughout the night, the dim Little Dipper “dumps water” into the bowl of the Huge Dipper approach down under. The Huge Dipper will dump it again within the evenings of spring.

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

It is an fascinating star: a magnetic white subgiant, spectral class A7m, 9 occasions brighter than the Solar and intently 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 viewpoint, dimming it by zero.24 magnitude. That is theoretically discernable by eye — however with no near-match comparability star proper close by, good luck. The system is simply 39 light-years away.


■ Cygnus the Swan floats nearly straight overhead these evenings. Its brightest stars kind the large Northern Cross.

Once you face southwest and crane your head approach, approach up, the cross seems to face upright. It is about two fists at arm’s size tall, with Deneb as its prime. Or to place it one other approach, whenever you face that route 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 Means working straight up from the west-southwest horizon, alongside the spine of Aquila and to the excellent of vivid Altair excessive within the south, alongside the shaft of the Northern Cross overhead, and straight down by Cassiopeia and northern Perseus to the east-northeast horizon.



This Week’s Planet Roundup

Mercury is hidden deep within the glow of sundown.

Venus, good at magnitude –four.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.eight and +zero.four, respectively, 16° aside on reverse sides of dim Capricornus.

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

Within the night search for 1st-magnitude Fomalhaut some 22° (two fists) decrease left of Jupiter. And fewer than 2° under or decrease left of Jupiter is Third-magnitude Delta Capricorni, described within the caption above.

Additionally, see Amateurs Spot New Influence 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.eight, on 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 depend upon longitude (primarily Moon positions) are for North America.

Japanese Daylight Time, EDT, is Common Time minus four hours. Common Time is also called UT, UTC, GMT, or Z time. To grow to be extra professional about time techniques than 99% of the individuals you may ever meet, see our compact article Time and the Novice Astronomer.

Need to grow to be a greater astronomer? Study your approach across the constellations. They’re the important thing to finding every little thing fainter and deeper to hunt with binoculars or a telescope.

That is an outside nature passion. For an easy-to-use constellation information masking the entire night sky, use the large month-to-month map within the heart of every situation of Sky & Telescope, the important journal of astronomy.

When you get a telescope, to place it to good use you may want an in depth, large-scale sky atlas (set of charts). The fundamental commonplace is the Pocket Sky Atlas (in both the unique or Jumbo Version), which exhibits stars to magnitude 7.6.

Pocket Sky Atlas cover, Jumbo editionThe Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and tons of of telescopic galaxies, star clusters, and nebulae amongst them. Proven right here is the Jumbo Version, which is in laborious covers and enlarged for simpler studying outdoor by crimson flashlight. Pattern charts. Extra concerning the present editions.

Subsequent up is the bigger and deeper Sky Atlas 2000.zero, plotting stars to magnitude eight.5; practically thrice as many. The subsequent up, as soon as you already know your approach round, are the even bigger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.zero (stars to magnitude 9.75). And be sure you learn Learn how to Use a Star Chart on the Telescope.

You may additionally desire a good deep-sky guidebook, comparable to the large Night time Sky Observer’s Information by Kepple and Sanner.

Can a computerized telescope change charts? Not for novices, I do not assume, and never on mounts and tripods which are lower than top-quality mechanically, that means heavy and costly. And as Terence Dickinson and Alan Dyer say of their Yard Astronomer’s Information, “A full appreciation of the universe can’t come with out growing the abilities to seek out issues within the sky and understanding how the sky works. This data comes solely by spending time below the celebs with star maps in hand.”

Audio sky tour. Out below the night sky along with your
earbuds in place, take heed to Kelly Beatty’s month-to-month
podcast tour of the heavens above. It is free.

“The hazards of not considering clearly are a lot larger now than ever earlier than. It isn’t that there is one thing new in our mind-set, it is that credulous and confused considering might be rather more deadly in methods it was by no means earlier than.”
            — Carl Sagan, 1996

“Details are cussed issues.”
            — John Adams, 1770


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