This Week’s Sky at a Glance, October 12 – 20

Moon, Jupiter, Saturn, Oct. 11-14, 2018

The waxing crescent Moon returns to evening twilight sky, posing with Jupiter and then Saturn. (The visibility of the fainter objects in bright twilight is exaggerated here.)

Friday, October 12

• Look lower left of the crescent Moon in twilight. Can you spot orange Antares, as shown here? For North Americans it's about 8° from the Moon, a little less than a fist at arm's length.

Way to the right of Antares shines brighter Jupiter.

• Then right around the end of twilight, you'll find zero-magnitude Arcturus shining 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 too — 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.

That bright point far upper right of Fomalhaut is Mars.

Saturday, October 13

• The crescent Moon hangs in the southwest after sunset, as shown above. How early in the fading light can you spot Saturn, about 14° to the Moon's left?

Next, look for fainter, more difficult Antares about the same distance to the Moon's lower right.

• Vega is the brightest star very high in the west. After nightfall is complete, look to Vega's right 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 right. Draco always eyes Vega!

Moon and Saturn, Oct 14-15, 2018

The Moon passing Saturn . . .

Sunday, October 14

• The "star" near the Moon tonight is Saturn, 3,900 times farther away.

• This being October, Deneb has replaced Vega as the zenith star after nightfall (for skywatchers at mid-northern latitudes). And, accordingly, dim Capricornus has replaced Sagittarius as the most notable constellation low in the south. Capricornus currently hosts bright Mars in its middle.

Monday, October 15

• The Big Dipper lies down horizontal low in the north-northwest late these evenings. How low? The farther south you are, the lower. Seen from 40° north (New York, Denver) even its bottom stars twinkle nearly ten degrees high. But at Miami (26° N) the entire Dipper skims along out of sight just below the northern horizon.

Tuesday, October 16

• First-quarter Moon (exact at 2:02 p.m. EDT). At nightfall the half-lit Moon shines in the south with Mars to its left, Saturn farther to its lower right, and Altair very high above it.

A finger-width above Altair is distant little Tarazed, magnitude 2.7.

Moon and Mars, Oct. 17-18, 2018

. . . and then it passes Mars.

Wednesday, October 17

• The Moon this evening shines to the right of Mars, 260 times farther away. Far to their lower left you'll find Fomalhaut (out of the frame here).

Thursday, October 18

• Now the Moon shines left (east) of Mars. Look to their lower left, by about two fists at arm's length, for Fomalhaut.

Friday, October 19

• The waxing gibbous Moon at dusk forms a right triangle (as seen from North America) with Mars to its right and Fomalhaut below it. Later in the evening, the triangle turns clockwise a bit as it wheels across the southern sky.

Saturday, October 20

• After dark, look upper left of the Moon, by two or three fists at arm's length, for the Great Square of Pegasus. It's standing on one corner and is a little more than a fist at arm's length in size.


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

Mars on October 10, 2018

Mars on October 10th, imaged by Christopher Go with a 14-inch scope. South is up. "Seeing was good today," he writes. "These images show Syrtis Major [the vertical dark 'peninsula' below center]. Hellas [the round bright area south of Syrtis Major] is the largest visible impact basin in the Solar System. Mare Tyrrhenum and Syrtis Minor [left of center] are well resolved. The Mitchel Mountains can be seen detached from the South Polar Cap."

Mercury and Venus are lost in the glare of the Sun.

Mars, moving eastward through central Capricornus, fades from magnitude –1.0 to –0.8 this week. It shines highest in the south soon after dark and sets around 1 a.m.

In a telescope Mars shrinks from 14 to 13 arcseconds wide this week, and it's as gibbous as we ever see it: only 86 percent sunlit. For a Mars map that displays which side is facing Earth at your time and date, use our Mars Profiler.

Jupiter (magnitude –1.8, in dim Libra) is very low in the west-southwest in mid-twilight and sets before twilight's end.

Can you still make out fainter Antares, magnitude +1.0, about 14° to Jupiter's left?

A bigger challenge: Can you detect fainter Delta (δ) Scorpii, currently magnitude +1.8 (it's variable), about midway between the two? Binoculars help. See the illustration at the top of this page.

Saturn (magnitude +0.5, in Sagittarius) glows yellow in the south-southwest in late dusk. It's about four fists at arm's length to the lower right of Mars.

Uranus, near the Aries-Pisces border, is easy in binoculars at magnitude 5.7 — with a good finder chart if you know the constellations well enough to see where to start.

Neptune, in Aquarius, is harder at magnitude 7.8. By mid-evening they're well up in the east and southeast, respectively. Finder charts for Uranus and Neptune, or see the September Sky & Telescope, page 48.


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


"Rational and innocent entertainment of the highest kind."
— John Mills, 19th century Scottish manufacturer and founder of Mills Observatory, on amateur astronomy.


"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


"Objective reality exists. Facts are often determinable. Vaccines save lives. Carbon dioxide warms the globe. Bacteria evolve to thwart antibiotics, because evolution. Science and reason are not a liberal conspiracy. They are how we determine facts. Civilization's survival depends on our ability, and willingness, to do this."
— Alan MacRobert, your Sky at a Glance editor


"Facts are stubborn things."
— John Adams, 1770

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