This Week’s Sky at a Glance, October 18 – 26

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Friday, Oct. 18

• Vega is the brightest star high in the west after dark. To its lower right by 14° (nearly a fist and a half at arm’s length), look for Eltanin, the nose of Draco the Dragon. The rest of Draco’s fainter, lozenge-shaped head is a little farther behind. Draco always eyes Vega.

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

Saturday, Oct. 19

• Vega shines high in the west after dark. About equally high in the southwest is Altair, not quite as bright. Just upper right of Altair, by a finger-width at arm’s length, spot little orange Tarazed. Down from Tarazed runs the stick-figure backbone of Aquila, the Eagle.

Waning Moon in Gemini at dawn, Oct. 20-21, 2019

On Sunday and Monday mornings the Moon displays itself in Gemini . . .

Waning Moon in Leo at dawn, Oct. 23-24, 2019

. . . and on Wednesday and Thursday mornings, the waning Moon says hello and goodbye to Regulus.

Sunday, Oct. 20

• Spot Altair high in the southwest soon after dark. Two distinctive little constellations lurk above it: Delphinus the Dolphin, hardly more than a fist at arm’s length to Altair’s upper left, and fainter Sagitta the Arrow, slightly less far to Altair’s upper right. Sky too bright? Use binoculars!

• At dawn on Monday the 21st the Moon is just a few hours from being exactly last quarter, as shown here. See next entry.

Monday, Oct. 21

• Last-quarter Moon; exactly so at 8:39 a.m. EDT. Many hours later, when the Moon rises around midnight or 1 a.m. tonight, the Moon’s terminator will already be looking just a little concave. The Moon will then be in dim Cancer, below Castor and Pollux and left of Procyon.

Binoculars will not only show the shape of the terminator better, they should also reveal the loose Beehive Star Cluster just a few degrees from the Moon within the same binocular field of view — if the air is sufficiently clear and clean.

By dawn Tuesday morning the Moon will be high in the southeast.

Tuesday, Oct. 22

• Deneb is the zenith star after nightfall (for skywatchers at mid-northern latitudes). Brighter Vega shines to its west. Altair shines farther down to Deneb’s south-southwest.

While it’s still twilight, draw a line from Deneb through the midpoint between Vega and Altair. Keep following this line way down, and you’ll hit Jupiter low in the southwest, on its way to setting.

Wednesday, Oct. 23

• It’s getting to be the time of year when the Big Dipper lies down horizontal low in the north-northwest in the evening. How low? The farther south you are, the lower. Seen from 40° north (New York, Peoria, 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.

Thursday, Oct. 24

• Look for Capella sparkling low in the northeast these evenings. Look for the Pleiades cluster, fingertip-size, about three fists at arm’s length to Capella’s right. These harbingers of the cold months rise higher as evening grows late.

Upper right of Capella, and upper left of the Pleiades, the stars of Perseus lie astride the Milky Way.

Friday, Oct. 25

The Ghost of Summer Suns. Halloween is approaching, and this means that Arcturus, the star sparkling low in the west-northwest in twilight, is taking on its role as “the Ghost of Summer Suns.” For several days centered on October 25th every year, Arcturus occupies a special place above your local landscape. It closely marks the spot where the Sun stood at the same time, by the clock, during hot June and July — in broad daylight, of course!

So, as Halloween approaches every year, you can see Arcturus as the chilly remaining ghost of the departed summer Sun.

Saturday, Oct. 26

• The W of Cassiopeia now stands vertically on end in the evening, high in the northeast. To its right, high in the east, are Andromeda and the corner-balanced Great Square of Pegasus.

________________________

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 you’ll need to know 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 really 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 and Venus are very low in bright twilight after sunset. Start by trying for Venus, magnitude –3.8. It’s just above the west-southwest horizon a mere 20 minutes after sunset. Binoculars will help.

To its left is Mercury, much dimmer at magnitude –0.1 all week. Their separation shrinks from 8° on October 18th to 5° on the 25th. Good luck; bring binoculars at least.

Mars (a mere magnitude +1.8, in Virgo) is a difficult catch just above the east horizon in early to mid- dawn. Again, you’ll need binoculars.

Jupiter (magnitude –2.0, in southern Ophiuchus) is the white dot low in the southwest as twilight fades.

Saturn on August 23rd. Even six weeks before quadrature, the globe’s black shadow on the rings was already fairly wide and prominent; it’s lower right of the globe here. South is up, celestial east is right. Damian Peach took this image remotely with the 1-meter Chilescope.

Saturn (magnitude +0.5, in Sagittarius) is the steady yellow “star” in the south-southwest during and after dusk. It’s 23° upper left of Jupiter.

Saturn is just two weeks past its eastern quadrature with the Sun, so from our viewpoint, the planet’s globe casts its shadow well eastward onto the rings, adding to the whole arrangement’s 3-D appearance in a telescope. And the rings are tilted 25° into our line of sight, nearly as open as we ever see them.

Below Saturn is the handle of the Sagittarius Teapot, highlighted by 2.0-magnitude Sigma Sagittarii (Nunki). Barely above Saturn is the dimmer, smaller bowl of the Sagittarius Teaspoon.

Uranus (magnitude 5.7, in southern Aries) is well up in the east by 9 p.m. daylight saving time. It’s highest in the south around midnight or 1.

Neptune (magnitude 7.8, in eastern Aquarius) is in high view in the southern sky these evenings. See our finder charts for Uranus and Neptune and Bob King’s story on observing 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





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