#astronomy This Week’s Sky at a Look, September 20 – 28

September 21, 2019 - Comment

Later this week, the waning crescent Moon lights the best way to Regulus and different stars of Leo earlier than and through early daybreak. Friday, Sept. 20 • Cassiopeia shows its flattened-W form excessive within the northeast these evenings. The W is tilted left. To the traditional Greeks Cassiopeia was a legendary African queen. Her

Moon and Leo at dawn, Sept. 25-27, 2019

Later this week, the waning crescent Moon lights the best way to Regulus and different stars of Leo earlier than and through early daybreak.

Friday, Sept. 20

• Cassiopeia shows its flattened-W form excessive within the northeast these evenings. The W is tilted left. To the traditional Greeks Cassiopeia was a legendary African queen. Her husband Cepheus, dimmer and extra sprawled out, is at present the subsequent constellation to her higher proper. Each lie alongside the winter Milky Manner.

• Within the middle of Cepheus, these moonless evenings are a superb time to deliver out your binoculars or scope and take a look at for the unusually small, compact open cluster NGC 7160 — as Matt Wedel tells within the September Sky & Telescope, web page 43.

Saturday, Sept. 21

• Final-quarter Moon (actual at 10:41 p.m. Jap Daylight Time). Tonight the Moon rises round midnight daylight-saving time, relying in your location. Look ahead to it to peek above the east-northeast horizon decrease proper of Capella and decrease left of the Pleiades.

By the primary signal of Sunday’s daybreak the Moon is shining excessive within the southeast, now with Orion to its decrease proper and Gemini to its decrease left. How typically do you study the Moon along with your telescope when the Moon is its late-night waning phases? To most of us, the waxing Moon of night is way more acquainted — when lunar mountains and crater partitions solid their shadows in the other way.

Sunday, Sept. 22

• Fall begins late tonight; the September equinox happens at three:50 a.m. September 23rd EDT. That is when the Solar crosses the equator (Earth’s equator and due to this fact the celestial equator too), heading south for the season. Dawn and sundown are very almost 12 hours aside, and the Solar rises and units virtually on the east and west factors in your horizon.

• Yearly round when summer season turns to autumn, Deneb takes over from brighter Vega because the zenith star after dusk (for skywatchers at mid-northern latitudes).

Monday, Sept. 23

• “My favourite observations enable me to make comparisons,” writes Matt Wedel within the October Sky & Telescope: “comparable objects at totally different distances, or objects of various sizes on the similar distance.” For binocular observers he affords some examples on the bowl of the Sagittarius Teaspoon, which is at present simply above the intense landmark Saturn. See his Binocular Spotlight column on web page 43 of the October difficulty.

Tuesday, Sept. 24

• Within the west, off to left of the Huge Dipper, brilliant Arcturus, the “Spring Star,” shines a little bit decrease at dusk every week. From Arcturus, the slim kite-shaped sample of Bootes extends 24° to the higher proper.

Wednesday, Sept. 25

• Earlier than and through daybreak on Thursday morning the 26th, look about three° proper of the crescent Moon for Regulus, as proven on the high of this web page (for the center of North America). Binoculars will assist with Regulus because the sky begins to develop brilliant.

Thursday, Sept. 26

• Right now of yr the wealthy Cygnus Milky Manner crosses the zenith in early night (for skywatchers at mid-northern latitudes). The Milky Manner extends straight up from the southwest horizon, passes overhead, and runs straight all the way down to the northeast.

Friday, Sept. 27

• Arcturus shines within the west as twilight fades out. Capella, equally brilliant, is barely rising within the north-northeast (relying in your latitude; the farther north you’re the greater it is going to be.) They’re each magnitude zero.

Later within the night, Arcturus and Capella shine on the similar peak of their respective compass instructions. When will this occur? That will depend on each your latitude and longitude.

When it does, flip to look southwest. There will likely be Jupiter at about the identical peak (relying in your latitude).

Look south-southeast, and there will likely be 1st-magnitude Fomalhaut about equally excessive too.

Saturday, Sept. 28

• The starry W of Cassiopeia stands excessive within the northeast after darkish. The appropriate-hand aspect of the W, the brightest aspect, is tilted up.

Look alongside the second phase of the W counting down from the highest. Discover the dim naked-eye stars alongside that phase (not counting its two ends). The brightest of those, on the precise, is Eta Cassiopeiae, magnitude three.four. It is a Solar-like star simply 19 light-years away with an orange-dwarf companion, a beautiful binary in a telescope.

The “one” on the left, fainter, is a naked-eye pair in a darkish sky: Upsilon1 and Upsilon2 Cassiopeiae, zero.three° aside. They’re orange giants unrelated to one another, 200 and 400 light-years away. Upsilon1, barely fainter, is the farther one.


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

That is an out of doors nature passion. For an easy-to-use constellation information overlaying the entire night sky, use the massive month-to-month map within the middle of every difficulty of Sky & Telescope, the important information to astronomy.

Jumbo Pocket Sky Atlas cover

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and tons of of telescopic galaxies, star clusters, and nebulae amongst them. Proven above is the Jumbo Version for simpler studying within the night time. Pattern chart.

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

Subsequent up is the bigger and deeper Sky Atlas 2000.zero, plotting stars to magnitude eight.5; almost 3 times as many. The subsequent up, as soon as you realize your means round, are the even bigger Interstellarum atlas (stars to magnitude 9.5) and Uranometria 2000.zero (stars to magnitude 9.75). And skim methods to use sky charts with a telescope.

You may additionally need a good deep-sky guidebook, resembling Sue French’s Deep-Sky Wonders assortment (which incorporates its personal charts), Sky Atlas 2000.zero Companion by Sturdy and Sinnott, or the larger Evening Sky Observer’s Information by Kepple and Sanner.

Can a computerized telescope substitute charts? Not for inexperienced persons, I do not suppose, and never on mounts and tripods which might be 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 not come with out growing the talents to seek out issues within the sky and understanding how the sky works. This data comes solely by spending time beneath the celebrities with star maps in hand.”

This Week’s Planet Roundup

Jupiter with Red Spot, Aug. 27, 2019

Jupiter on August 27th with the Nice Pink Spot close to the central meridian, imaged by Damian Peach with the 1-meter Chilescope. “It is fairly superb simply how totally different [the Red Spot’s] area seems in comparison with again in Might-June,” he writes. South is up.

Mercury, Venus, and Mars stay deep within the glare of the Solar.

Jupiter (magnitude –2.1, between the toes of Ophiuchus) is the white dot low within the south-southwest as twilight fades away. Orange Antares, a lot fainter at magnitude +1.zero, twinkles 9° to its decrease proper. It is a poor season for Jupiter telescopically. Not solely is the low-altitude seeing a large number, however Jupiter has shrunk to only 37 arcseconds huge.

Saturn on August 23rd, imaged by Damian Peach with the 1-meter Chilescope. South is up.

Saturn (magnitude +zero.four, in Sagittarius) is the regular yellow “star” within the south throughout and simply after nightfall. It is 27° higher left of Jupiter. Beneath Saturn is the deal with of the Sagittarius Teapot. Barely above it’s the dimmer, smaller bowl of the Teaspoon.

Uranus (magnitude 5.7, in Aries) is effectively up within the east by 10 or 11 p.m. daylight saving time and highest within the south round 2 or three a.m.

Neptune (magnitude 7.eight, in Aquarius) is effectively up within the southeast by 9 or 10 p.m. and highest within the south round 11 or midnight. See Bob King’s article on observing Neptune and our finder charts for Uranus and Neptune.


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.

Jap Daylight Time (EDT) is Common Time (UT, UTC, GMT, or Z time) minus four hours.


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 is free.


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

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