This Week’s Sky at a Glance, October 4 – 12

Moon and Saturn, Oct. 4-5, 2019

The Moon poses with Saturn on the evenings of the 4th and 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, Oct. 4

• The waxing Moon this evening shines between Saturn, to its left or upper left, and Jupiter farther to the Moon's lower right (off the center-right of the chart here).

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), nicely placed high in the sky in 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 a magnitude-8.7 orange pinpoint four ring-lengths to Saturn's east. Yet Titan is, in reality, half again as large in diameter as our Moon.

Sunday, Oct. 6

• Cygnus the Swan flies nearly straight overhead these evenings. Its brightest stars form the big Northern Cross. When you face southwest and crane your head up, the cross appears to stand upright. It's about two fists at arm's length tall, with Deneb as its top. Or to put it another way, the Swan is diving down.

Monday, Oct. 7

• Even as the stars begin to come out in twilight now, Cassiopeia is already higher in the northeast than the sinking Big Dipper is in the northwest. Cassiopeia's broad W pattern is tilting toward vertical.

Tuesday, Oct. 8

• Look lower left of the waxing gibbous Moon this evening, by about two fists at arm's length, and there will be Fomalhaut, the lonely Autumn Star twinkling away. It's particularly far from any other 1st-magnitude star, and the rest of its constellation — Piscis Austrinus, the Southern Fish — is extraordinarily dim.

Wednesday, Oct. 9

• Now Fomalhaut is nearly straight below the Moon after dark.

• Vega is the brightest star very high in the west at nightfall. Arcturus, equally bright, is getting quite low in the west-northwest. The brightest star in the vast expanse between them, about a third of the way from Arcturus up toward Vega, is Alphecca, magnitude 2.2 — the crown jewel of Corona Borealis. Alphecca is an eclipsing binary with a 17-day period, but its brightness dips are too slight for the eye to discern reliably.

Thursday, Oct. 10

• Look to the right of Vega by 14° (nearly a fist and a half at arm's length) for Eltanin, the nose of Draco the Dragon. The rest of Draco's fainter, lozenge-shaped head is a little farther behind. Draco is always eyeing Vega.

The main stars of Vega's own constellation Lyra, faint by comparison, now extend to Vega's left (by 7°).

Friday, Oct. 11

• Soon after dark, you'll find zero-magnitude Arcturus low in the west-northwest at the same height as zero-magnitude Capella in the northeast. When this happens, turn to the south-southeast, and there will be 1st-magnitude Fomalhaut at the same height — if you're at latitude 43° north. Seen from south of that latitude Fomalhaut will appear higher; from north of there it will be lower.

And whatever your latitude, in the southwest at that time you'll find bright Jupiter about as high as Fomalhaut.

Saturday, Oct. 12

• Look above the nearly-full Moon this evening for the Great Square of Pegasus through the moonlight. It's balancing on one corner, and your fist at arm's length fits inside it. For your location, when it is exactly balanced? That is, when is the Square's top corner exactly above its bottom corner? This will probably by sometime soon after the end of twilight, depending on your latitude. Try lining up the stars with the vertical edge of a building as a measuring tool.

________________________

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, in the feet of Ophiuchus) is the white dot low in the southwest as twilight fades. Can you still spot Antares, one sixteenth as bright at magnitude +1.0, 10° to Jupiter's lower right?

Saturn (magnitude +0.5, in Sagittarius) is the steady yellow "star" in the south-southwest during and after dusk. It's 25° 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. Binoculars help through the moonlight!

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 1 or 2 a.m.

Neptune (magnitude 7.8, in Aquarius) is in the southeast after dark and highest in the south by 10 or 11. 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

4 thoughts on “This Week’s Sky at a Glance, October 4 – 12

  1. RodRod

    mary beth et al. I did enjoy a great time outdoors last night from 7:00 PM until 10:45 PM EDT. Great views of Saturn (the shadow was on the rings), waxing crescent Moon, and earlier, Jupiter with Great Red Spot near the limb (GRS transited near 5:41 PM). M15 globular cluster and M31 with its two companion dwarfs too along with milky arms across the field of view and hint of dust lanes (35x views). I used my 10-inch Newtonian and with the 2-inch eyepiece – the Moon punches you in the eye. I need to get another, larger moon filter 🙂 Two stars in Sagittarius less than 7 arcminute from the lunar limb with earthshine very visible in the field view. October skies can be great!

  2. mary bethmary beth

    Ouch!! I’ve looked at the moon through my neighbor’s high-powered telescope and I remember the discomfort!! Sounds like you had a great Friday night! We have had clear skies and it’s just been enjoyable viewing the autumn configuration, I especially like to see Arcturus low in the northwest and enjoy sky and telescope calling it “the ghost of the summer suns” close to Halloween. I still have a pretty good view of Antares. Did you often view the Corona Borealis with your scope?

  3. RodRod

    mary beth, no I do not view Corona Borealis with my scopes but I use those stars to check limiting magnitude like Nu1 & 2 Coronae Borealis near +5.4/5.5 or so. On 06-May-19, I checked Eta Coronae Borealis near 5.56 and could see it. I have a good Moon filter for 1.25-inch eyepieces but not for my 2-inch eyepiece. I plan to purchase one though. The 2-inch eyepiece provides a very good, wide field view of the Moon at about 35x using my 10-inch scope with a field of view 1.8/1.9 degrees across. Enjoy October skies 🙂

  4. uwidavid

    I must disagree that Venus and Mercury are too low.
    Mercury actually seems quite high (for Mercury) and Venus being so bright is a easy spot just after sunset with Mercury much higher and to the left (on October 5th).

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