This Week’s Sky at a Glance, October 20 – 28

This Week’s Sky at a Glance, October 20 – 28

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Cassiopeia and Double Cluster. Akira Fujii photo.

This week, the big W of Cassiopeia stands almost on end high in the northeast. Below it, binoculars will show the Double Cluster of Perseus.

Friday, October 20

• The modest Orionid meteor shower continues in the early-morning hours for the next couple of nights. The apparent radiant point of the shower is near Orion's Club, low in the east after midnight and high in the south by the beginning of dawn. The morning sky is free of moonlight. See Orionid Meteors Max Out Sunday Morning.

• Look for Capella sparkling low in the northeast after dinnertime this week. Then find the little Pleiades cluster to its right by about three fists at arm's length. They rise higher as evening grows late, harbingers of the cold months to come.

Upper right of Capella, and upper left of the Pleiades, the stars of Perseus stand astride the Milky Way. To the upper left of Perseus, the Milky Way runs through Cassiopeia.

Saturday, October 21

• After dark, spot the W of Cassiopeia high in the northeast. It's standing almost on end. The third segment of the W, counting down from the top, points almost straight down. Extend that segment twice as far down as its own length, and you're at the Double Cluster in Perseus. This pair of star-swarms is dimly apparent to the unaided eye in a dark sky (use averted vision), and it's visible from almost anywhere with binoculars. It's a lovely sight in telescopes.

Moon and Saturn at dusk, Oct. 22-24, 2017

Newly returned to the evening sky, the waxing crescent Moon passes low Antares (use binoculars!) and then Saturn in the southwestern twilight.

Sunday, October 22

• This is the time of year when the Big Dipper lies down horizontal low in the north-northwest after dark. 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.

Monday, October 23

• Look low in the southwest in late twilight for Saturn glowing about 7° left of the waxing crescent Moon (as seen from North America), as shown here.

Tuesday, October 24

• Now, at dusk, Saturn appears about 6° to the lower right of the thickening Moon, as shown here.

Wednesday, October 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."

What does this mean? 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 ghost of the departed summer Sun.

Thursday, October 26

• Draw a line from Altair, the brightest star very high above the Moon in the southwest after dark, to the right to brighter Vega, very high in the west. Continue the line half as far onward, and you hit the Lozenge: the pointy-nosed head of Draco, the Dragon. Its brightest star is orange Eltanin, the tip of the Dragon's nose, which points toward Vega.

Friday, October 27

• First-quarter Moon (exactly first-quarter at 6:22 p.m. Eastern Daylight Time). At nightfall, you'll find Altair shining about 30° (three fists at arm's length) to the Moon's upper right.

Much closer to the Moon's upper right, by only about 6°, are 3rd-magnitude Alpha and Beta Capricorni. Alpha is the upper one. Can you resolve Alpha into a tiny twin pair with your unaided eyes? Binoculars make it easy — and should also resolve Beta, another wide double, although its components are somewhat closer and very unequal.

Saturday, October 28

• Now Altair appears a little farther to the Moon's upper right after dark. Just upper right of Altair, by a finger-width at arm's length, is orange Tarazed. It looks like Altair's little sidekick, but it's actually a much bigger and brighter star far in the background. Altair is 17 light-years away. Tarazed is about 360 light-years away and 100 times as luminous.

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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.

Pocket Sky Atlas, jumbo edition

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. Larger view. 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, is the even larger 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 is hidden in the glare of the Sun.

Venus (magnitude –3.9) rises around the beginning of dawn and shines very low due east as dawn brightens.

Mars (magnitude +1.8, only 1/200 as bright as Venus) is higher in the dawn, to the upper right of Venus and widening. Their separation grows from 10° on October 21st to 14° by the 28th. Venus is slowly getting lower, Mars higher.

Jupiter is out of sight, passing through conjunction behind the Sun.

Saturn (magnitude +0.5, in southern Ophiuchus) glows low in the southwest at dusk.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are well up after dark in the east and southeast, respectively. Use our finder charts online or in the October Sky & Telescope, page 50.

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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.

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"This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours."
— Neil deGrasse Tyson, 2014

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"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 fake, are not a political conspiracy. They are how we discover reality. Civilization's survival depends on our ability, and willingness, to use them."
— Alan MacRobert, your Sky at a Glance editor

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

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