This Week’s Sky at a Glance, September 27 – October 5

Moon and Jupiter, Oct. 2-3, 2019

The waxing Moon re-enters the evening sky this week, shining with Jupiter on October 3rd.

Moon and Saturn, Oct. 4-5, 2019

. . . and then with Saturn on the 5th. (The blue 10° scale is about the width of your fist at arm's length. The Moon's position is exact for an observer near the middle of North America. The apparent sizes of the Moon, planets, and stars are exaggerated for clarity.)

Friday, Sept. 27

• Arcturus shines in the west as twilight fades out. Capella, equally bright, is barely rising 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 the same height in their respective compass directions.

When will this happen? That depends on both your latitude and longitude. When it does, turn to look southwest. There will be Jupiter at about the same height (depending on your latitude).

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

Saturday, Sept. 28

• The starry W of Cassiopeia stands high in the northeast after dark. The right-hand side of the W, the brightest side, is tilted up.

Look along the second segment of the W counting down from the top. Notice the dim naked-eye stars along that segment (not counting its two ends). The brightest of these, on the right, is Eta Cassiopeiae, magnitude 3.4. It's a Sun-like star just 19 light-years away with an orange-dwarf companion, a lovely binary in a telescope.

The "one" on the left, fainter, is a naked-eye pair in a dark sky: Upsilon1 and Upsilon2 Cassiopeiae, 0.3° apart. They're orange giants unrelated to each other, 200 and 400 light-years away. Upsilon1, slightly fainter, is the farther one.

• New Moon (exact at 2:26 p.m. Eastern Daylight Time).

Sunday, Sept. 29

Vertical Milky Way over Estonia

The Milky Way now stands straight up from the south-southwest horizon after dark, like firelit smoke rising from some huge, ghostly campfire, if you're in the world's mid-northern latitudes. Robert Sälg took this shot from Vorumaa, Estonia, latitude 58°, rather far north — which is why the Sagittarius star clouds are so low in the trees, and why the bluer Cygnus Star Cloud isn't as high as it "should" be. Click to enlarge.

• At this time of year the rich Cygnus Milky Way crosses the zenith soon after dark (for mid-northern latitudes). The Milky Way extends straight up from the southwest, like firelit smoke from some great dim campfire. It passes overhead, then runs straight down to the northeast — where it plummets through Cassiopeia, Perseus, and low Auriga.

• Algol in Perseus shines at its minimum brightness (magnitude 3.4 instead of its usual 2.3) for a couple hours centered on 12:34 a.m. tonight EDT, 9:34 p.m. PDT.

Monday, Sept. 30

• "My favorite observations allow me to make comparisons," writes Matt Wedel in the October Sky & Telescope: "similar objects at different distances, or objects of different sizes at the same distance." For binocular observers he offers some examples at the bowl of the Sagittarius Teaspoon, just above bright Saturn. See his Binocular Highlight column on page 43 of the October issue.

Tuesday, Oct. 1

• In the west, way left of the Big Dipper, shines bright Arcturus, the "Spring Star," a little lower at nightfall each week. From Arcturus, the narrow kite-shaped pattern of Bootes extends 24° to the upper right.

Wednesday, Oct. 2

• The crescent Moon at dusk forms a triangle with Jupiter to its left and dimmer Antares closer to the Moon's lower left, as shown at the top of this page.

• Algol is at its minimum brightness for a couple hours centered on 9:23 p.m. EDT.

Thursday, Oct. 3

• The thick crescent Moon this evening shines with bright Jupiter, as shown at the top of this page. Jupiter, though, is 2,200 times farther away. Its four big moons, visible in any telescope as 5th and 6th magnitude dots, are roughly our own Moon's size.

Friday, Oct. 4

• Now the waxing Moon shines between Jupiter and Saturn.

Saturday, Oct. 5

• It's both International Astronomy Day and International Observe the Moon Night! The Moon is first quarter (exactly so at 12:47 p.m. EDT), well placed high in the sky during early evening with its shadow-displaying terminator running right down the middle of the disk.

Moreover, this evening the Moon has Saturn as a companion — another top target for small scopes. As seen from North America, Saturn is only about 2° to the Moon's right or upper right. Perfect for setting up your scope in a public place and offering views of both as a sidewalk astronomer.

You can point out that Saturn is 3,800 times farther away. A telescope this evening will show its own largest satellite, Titan, as just a magnitude-8.7 orange pinpoint four ring-lengths to Saturn's east. Yet Titan is half again as large in diameter as our Moon.

________________________

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 guide to astronomy.

Jumbo Pocket Sky Atlas cover

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Sample chart.

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.

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) and Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger 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."


This Week's Planet Roundup

Mercury, Venus, and Mars remain deep in the glare of the Sun.

Jupiter (magnitude –2.0, between the feet of Ophiuchus) is the white dot low in the southwest as twilight fades away. Orange Antares, one sixteenth as bright at magnitude +1.0, twinkles 10° to Jupiter's lower right.

This is a lousy time for Jupiter telescopically. Not only is the low-altitude seeing a mess, but Jupiter has shrunk to just 36 arcseconds wide.

Saturn this week remains low over the Sagittarius Teapot.

Saturn (magnitude +0.5, in Sagittarius) is the steady yellow "star" in the south during and after dusk. It's 26° upper left of Jupiter. Below Saturn is the handle of the Sagittarius Teapot. Barely above it is the dimmer, smaller bowl of the Sagittarius Teaspoon.

Uranus (magnitude 5.7, in Aries) is well up in the east by 10 p.m. daylight saving time. It's highest in the south around 2 a.m.

Neptune (magnitude 7.8, in Aquarius) is in the southeast after dark and highest in the south around 11 p.m. See Bob King's story on observing Neptune and our finder charts for Uranus and Neptune.


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 (UT, UTC, GMT, or Z time) minus 4 hours.


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

9 thoughts on “This Week’s Sky at a Glance, September 27 – October 5

  1. TonyTony

    Venus has begun to emerge in the evening sky. With help from 16X50 binoculars, I saw it soon after sunset on September 28 despite its small elongation and unfavourable inclination of the ecliptic (I’m on Vancouver Island at latitude 48+).

    1. RodRod

      Tony, that is a good observation on Venus. Mars, Venus, and Mercury tracked near the Sun along the ecliptic for sometime now. In my location in Maryland (Patuxent river farms), near 38.8 N latitude, Venus will set tonight about 1926 EDT, Mercury 1933 EDT. The Sun at my location tonight sets 1851 EDT, so Venus and Mercury are slowly coming back into view but very low shortly after sunset. I have not bothered a view yet though.

    2. Jakob

      On september 21 I saw Venus in my 8 x 40 binos at sunset.
      I could not see fainter Mercury because the sky was too brigtht. Only 3,5° away from Venus. Jakob reporting from further north at 56° N in Scandinavia.

  2. RodRod

    mary beth in Houston, how is it going after the rains in your area? I have rain now today but later, looks like some more clear skies for stargazing and Saturday night here, the First Quarter Moon close to Saturn, about 2 degrees apart in the evening sky.

    1. mary bethmary beth

      Hi Rod! Last week was a mess but thankfully I have never had water in my home. The skies have cleared up pretty nicely and it was beautiful tonight. Is Jupiter getting brighter again or is it my imagination? I know it was extra bright I believe back in May but it seemed really bright tonight. Looking forward to the moon and Saturn, thank you for letting me know! I think we’re going to get our first cool front a week from today, which for Houston means we might stay below 90°. Should give us some clear skies also! I’ve been enjoying watching Arcturus, and I can still see Antares pretty well. I’ve also been enjoying watching Formalhaut get more and more visible. Was wondering how well you can see that lovely star?

  3. RodRod

    mary beth, glad to read your comments and no issues for you with the heavy rains that came. *Is Jupiter getting brighter again or is it my imagination?* Jupiter is fading now, the apparent brightness slowly dimming as the distance increases as well as Jupiter’s disk size in telescope views. You can track monthly details in Sky & Telescope magazine like the October issue. The Planetary Almanac is published each month with ephemeris table showing the changes for the Sun through Neptune. October issue is page 44. Another good source is Stellarium 0.19.1, a free down load application. SkySafari works for Apple IOS tools and I use Starry Night Pro Plus 8 on Windows 10 desktop. I recently enjoyed watching an Io shadow transit cross Jupiter using my 3.6-inch refractor and 10-inch Newtonian (excellent views). Some great views of Saturn too in Sagittarius. Looks like Friday night here will be cool with temps in upper 40s and clear skies. If it is, I plan to be out and hooting at the owls too 🙂

  4. RodRod

    mary beth, quick note on Fomalhaut star at my location. Yes I can see Fomalhaut from near 38.8 N latitude. Tonight the star transits my location near 2324 EDT at an altitude close to 22 degrees elevation. Fomalhaut has an exoplanet too, an exoplanet I cannot see using my 10-inch 🙂

      1. RodRod

        mary beth, yes Fomalhaut b. No I have never observed this exoplanet. It seems only the big, professional tools are capable of this. Apparent brightness of host star, apparent magnitude of the exoplanet, angular separation between host star and exoplanet, ability to resolve the two, etc. Friday still looks good here for some fun under the early Fall skies, the moon is approaching First Quarter too.

All comments must follow the Sky & Telescope Terms of Use and will be moderated prior to posting. Please be civil in your comments. Sky & Telescope reserves the right to use the comments we receive, in whole or in part, and to use the commenter’s username, in any medium. See also the Terms of Use and Privacy Policy.

COMMENT

This site uses Akismet to reduce spam. Learn how your comment data is processed.