This Week’s Sky at a Glance, October 15 – 23 – Sky & Telescope

We can’t look away. Long-lasting, ever fluctuating Nova Cassiopeiae 2021 was finally down to about magnitude 8.2 as of October 14th. That’s still barely fainter than when it exploded last March. Charts and comparison stars.

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FRIDAY, OCTOBER 15

■ Bright Jupiter and fainter Saturn continue to dominate the southern evening sky from dim Capricornus, as shown above. They remain 15° apart; both are nearly stationary at the west end of their retrograde loops.

■ Spot Venus low in the west in twilight. Just lower left of it, by 1½° (about a finger width at arm’s length), look for orange Antares. It’s less than 1% as bright. Venus stays about this close to Antares for the next two days, but watch their orientation change.

SATURDAY, OCTOBER 16

■ It’s International Observe the Moon Night, with more than 1,860 events worldwide inviting you to show up. Or put on your own event and add it to the map! All you need to host a Moon-observing event is a telescope, a place to put it, and a readiness to welcome visitors for a look.

The Moon is waxing gibbous. Its terminator crosses Oceanus Procellarum, which shows off the dramatic crater Copernicus and countless other features.

To the naked eye, the Moon forms a roughly equilateral triangle with bright Jupiter to its right or upper right and Fomalhaut to the Moon’s lower right.

Cloudy where you are? Gianluca Masi of the Virtual Telescope Project plans a narrated live feed of the Moon from Rome, starting at 17:30 UT (3:30 p.m. EDT).

SUNDAY, OCTOBER 17

■ This is the time of year when, in early evening, W-shaped Cassiopeia stands on end high in the north-northeast — and when, off to its lower left in the north, the dim Little Dipper extends leftward from Polaris.

Below or lower right of Cassiopeia is star-scattered Perseus. Look lower left from Perseus, or far below Cas, for bright (zero-magnitude), twinkly Capella.

MONDAY, OCTOBER 18

■ Vega is the brightest star very high west of the zenith after dark. Less high in the south-southwest is Altair, not quite as bright. Still near the zenith is the third and least bright star of the Summer Triangle, Deneb.

Look lower left from Altair by three or four fists at arm’s length, and you hit can’t-miss-it Jupiter. Extend the line two fists farther on down, and you hit Fomalhaut.

TUESDAY, OCTOBER 19

■ Look two fists left of the bright Moon this evening for the brightest stars of Aries not far apart. Through the moonlight, can you see one of them, or two, or three? Hamal is magnitude 2.0. Sheratan to its right or upper right is is mag 2.6. Mesarthim, closer to the lower right of Sheratan, is more challenging at mag 3.9.

WEDNESDAY, OCTOBER 20

■ Full Moon (exact at 10:57 a.m. EDT). The Moon rises in the east about 20 minutes after sunset (for the mid-latitudes of North America). Right after dark, look three fists above the Moon for Alpheratz, the 2nd-magnitude head of Andromeda and the leftmost corner of the Great Square of Pegasus.

■ It’s a busy evening at Jupiter. At 8:41 p.m. EDT the tiny black shadow of Io starts crossing Jupiter’s face, entering on the east limb, followed by Io itself about an hour later. The shadow leaves Jupiter’s western limb at 10:58 p.m. EDT, followed by Io an hour after that.

Meanwhile, Jupiter’s Great Red Spot should transit the planet’s central meridian around 10:37 p.m. EDT. Features on Jupiter remain closer to the central meridian than the limb for 50 minutes before and after they transit.

THURSDAY, OCTOBER 21

■ Once the Moon is well up in the east tonight, look left of it by about a fist and a half for the little Pleiades cluster. Can you pick out this sparkle-patch through the moonlight? Binoculars make it easy.

Look a little more than a fist below the Pleiades for orange Aldebaran on the rise.

FRIDAY, OCTOBER 22

■ The waning gibbous Moon shines in the east after dark this evening. You may need binoculars to pick out the Pleiades few degrees to its left or upper left, as shown below. Much easier is bright Capella many times farther left of the Moon.

As night advances, Aldebaran comes up below or lower left of the Moon. And by midnight, Orion is clearing the eastern horizon far below them all.

SATURDAY, OCTOBER 23

■ Tonight the waning Moon shines near Aldebaran, as shown below.

■ 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, Madrid) 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.

 

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This Week’s Planet Roundup

Mercury is heading toward its best morning apparition of the year. By about October 18th, look for it low above the east horizon about 50 minutes before sunrise. On that morning it’s still only magnitude +0.7, so you may want binoculars.

But it’s brightening and getting a little higher every day. Just four days later, on Friday morning the 22nd, Mercury is more than twice as bright at magnitude –0.2. Next week it will nearly double in brightness again.

Don’t confuse Mercury with Arcturus, which is above the east-northeast horizon (depending on your latitude) off to Mercury’s left.

Mars remains out of sight behind the glare of the Sun.

Venus, brilliant at magnitude –4.4, shines in southwest during twilight, crossing from Scorpius into the feet of Ophiuchus. It sets about a half hour after twilight’s end.

On Saturday the 16th Venus is passing 1.4° north (upper right) of Antares, which is much fainter, orange, and twinkling. Even evening thereafter, Antares falls away farther to Venus’s lower right. By the 22nd they’re a good 6° apart.

Jupiter and Saturn continue to shine in the south during evening, 15° apart on opposite sides of Capricornus. Jupiter is the eye-grabber at magnitude –2.6. Saturn, to its right or lower right, is a twentieth as bright at mag +0.6.

In twilight they shine equally high. As the evening progresses watch them tilt as they move to the right, with Saturn becoming the lower one. Saturn sets around midnight or 1 a.m. daylight-saving time, followed by Jupiter about an hour later.

After dark look 23° (two fists at arm’s length) lower left of Jupiter for 1st-magnitude Fomalhaut, as shown at the top of this page.

Here’s a beginner’s telescopic guide to Jupiter.

Uranus (magnitude 5.7, in southern Aries) climbs high in the east by 10 p.m.

Neptune (magnitude 7.8, at the Aquarius-Pisces border) is already well up in the in the southeast at twilight’s end.

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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 minus 4 hours. Universal Time is also known as UT, UTC, GMT, or Z time. To become more expert about time systems than 99% of the people you’ll ever meet, see our compact article Time and the Amateur Astronomer.

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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 magazine of astronomy.

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) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read How to Use a Star Chart with a Telescope.

You’ll also want a good deep-sky guidebook, such as the big 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.”

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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.

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“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

“Facts are stubborn things.”
            — John Adams, 1770

 

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