This Week's Sky at a Glance, May 15 – 23

By: Alan MacRobert May 15, 2020 0

Supernova in Leo, magnitude 12.7. A Type-Ia supernova in visual range of 6-or 8-inch scopes has erupted in NGC 3643 south of the hind foot of Leo, high after dark. As of May 18th, SN 2020hvf was about magnitude 12.7 and outshining its faint host galaxy. Meanwhile, a much deeper challenge is 14.6-magnitude SN 2020jfo in M61 in Virgo, also high these evenings. See Supernovae Light Up in M61 and NGC 3643.

Comet SWAN: Yet another fizzler! (Updated May 18.) Comet SWAN (C/2020 F8), now low above the pre-dawn horizon for mid-northern observers, has been fading fast, passing 6th and 7th magnitude on the way down, rather than brightening to 3rd magnitude as it approaches its May 27th perihelion as once predicted. It's crossing Perseus for the rest of May. This week it's low in the northeast just before the very beginning of dawn (about an hour and 50 minutes before your local sunrise time, depending on your latitude). You'll a telescope and an open view low to the northeast. See Bob King's Comet SWAN charts. Good luck.

FRIDAY, MAY 15

■ A naked-eye Venus challenge! All week in twilight, the large, thin crescent of Venus is easy to discern with a small telescope or even good, steadily braced binoculars.

But can you resolve the crescent with your unaided eyes? Mere 20/20 vision isn't good enough; success may await the eagle-eyed with 20/15, 20/12, 0r (rare) 20/10 vision. Try during different stages of twilight before the sky becomes too dark and Venus's glare too spready. Look long and carefully and report your results to Sky & Telescope's Bob King, [email protected], as told in the May 2020 issue, page 49.

You may improve your chances by sighting through a clean, round hole in a stiff piece of paper 1 mm, 2mm, or 3mm in diameter (try then all). This will mask out optical aberrations that are common away from the centers of your eye's cornea and lens.

One person who apparently succeeded was Edgar Allan Poe. An amateur astronomer since boyhood, he used a naked-eye sighting of Venus's crescent as the central event in his poem "Ulalume" (1847) near the end of his life. Before dawn, a bereaved lover roams a misty October woodland accompanied by "Psyche, my soul." Ahead of them low in the east, where the constellation Leo ascends before dawn in mid-autumn, they witness the new-risen Venus, star of romantic love in Roman mythology, coming "up through the lair of the Lion." Poe refers to the planet as Astarte — the wilder, more wanton Greek version of the Romans' Venus goddess:

And now, as the night was senescent,
And star-dials pointed to morn —
As the star-dials hinted of morn —
At the end of our path a liquescent
And nebulous lustre was born,
Out of which a miraculous crescent
Arose with a duplicate horn—
Astarte's bediamonded crescent
Distinct with its duplicate horn.

Poe compares its passionate brilliance to cooler, more composed Dian, the horned crescent Moon, and urges Psyche forward:

Let us on by this tremulous light!
Let us bathe in this crystalline light!

But Psyche, who knows better, is terrified, and this being Poe, it doesn't end well.

Poe's narrator peering at a pre-dawn crescent Venus, "distinct with its duplicate horn," as Psyche, his winged soul, begs him away. Studies by Dante Gabriel Rossetti, circa 1847–1848. The figures on the right are a preliminary sketch, followed by the more powerful version on the left.

Poe wrote "Ulalume" in the fall of 1847. Before dawn on November 4, 1847, a crescent Venus and crescent Moon ("Dian") indeed hung near each other low in the east below Leo — in Poe's "lair of the Lion," the sky area from which the traditional Leo figure stalks upward in spring.

Venus was there a couple weeks earlier, too, during the mid- and late "lonesome October" of that most immemorial year as a larger, thinner, more easily resolvable crescent, though the Moon at that time was absent.

SATURDAY, MAY 16

■ The Arch of Spring sinks lower. All week, look west-northwest at nightfall for Pollux and Castor. They're lined up almost horizontal (depending on your latitude), some 30° upper left of brilliant Venus: about three fists at arm's length.

Pollux and Castor form the top of the enormous Arch of Spring. Lower left of them is Procyon, the left end of the Arch. Farther to their lower right is the other end, formed by Menkalinan (Beta Aurigae) and then brilliant Capella. Venus shines below the Arch's right side.

SUNDAY, MAY 17

■ These dark spring evenings, the long, dim sea serpent Hydra snakes level far across the southern sky. Find his head, a rather dim asterism about the width of your thumb at arm's length, in the southwest. Look for it to the upper left of Procyon, the brightest star low due west, by about a fist and a half.

Hydra's brightest star is Alphard, his 2nd-magnitude orange heart, a fist and a half left of his head.

Hydra's tail stretches all the way to Libra rising in the southeast. Dim Crater and brighter Corvus ride on his back.

MONDAY, MAY 18

■ Before the Moon comes back into the evening sky, explore the galaxies at the head of Bootes — including as many as three three knife-thin, edge-on spirals if you have 8 to 14 inches of aperture — using the Deep-Sky Wonders article, chart, and photos in the June Sky & Telescope, page 54. And with large binoculars or a small rich-field scope, piece out the Kangaroo asterism inside Bootes's head.

TUESDAY, MAY 19

■ Zero-magnitude Vega dominates the east-northeastern sky as evening advances. Look for its faint little constellation Lyra, the Lyre, hanging down from it. The most familiar part of Lyra is a small, almost-equilateral triangle with Vega as its top corner, and a larger parallelogram hanging to the lower right from the triangle's bottom corner.

The bottom two stars of the parallelogram, Beta and Gamma Lyrae, are the two brightest stars of the pattern after Vega.

WEDNESDAY, MAY 20

■ This is the time of year when Leo walks downward in the southwest during evening, on his way to departing into the sunset in early summer. Right after dark, spot the brightest star high in the west-southwest. That's Regulus, his forefoot.

■ With summer exactly a month away (astronomically speaking), the last star of the Summer Triangle doesn't rise above the eastern horizon until about 10 or 11 p.m. That's Altair, the Triangle's lower-right corner. Vega is its highest and brightest corner. Watch for Altair to clear the horizon three or four fists at arm's length to Vega's lower right.

The third star of the Triangle is Deneb, sparkling less far to Vega's lower left.

Catch Venus and Mercury in conjunction on the 21st, only 1° apart during twilight for North America. That's a little less than a finger's width at arm's length.

THURSDAY, MAY 21

■ Venus and Mercury are in conjunction in the west-northwest in evening twilight, as shown above. Venus outshines Mercury by 30 times, something the illustration does not convey. Although they look close together, Mercury is on the far side of the Sun from us while Venus is now on the near side. So Mercury this evening is 3.5 times more distant. It's 9.1 light-minutes from us, compared to Venus's distance of 2.6 light-minutes.

■ Can you see the big Coma Berenices star cluster? Does your light pollution really hide it, or do you just not know exactly where to look? It's 2/5 of the way from Denebola (Leo's tail tip) to the end of the Big Dipper's handle (Ursa Major's tail tip). Its brightest stars form an inverted Y. The entire cluster is about 5° wide — a big, dim glow in a dark sky. It nearly fills a binocular view.

How fast they move! Venus is heading down toward the lower right day by day, while Mercury is ascending to the upper left.

FRIDAY, MAY 22

■ Mercury and Venus are still close together, 1.7° apart, as shown above. Think photo opportunity. Put your camera or phone on a tripod, zoom in as far as you can, and carry the setup around to get interesting foreground to frame the planets.

■ New Moon (exact at 1:39 p.m. Eastern Daylight Time).

Now, as the thin crescent Moon makes its monthly reappearance, while Venus and Mercury form a nice triangle with much fainter Beta Tauri. The triangle, which changes from day to day, is 3° or 4° on a side. The visibilities of faint objects are exaggerated here.

SATURDAY, MAY 23

■ An very tricky photo opportunity! Set up early to catch the super-thin crescent Moon, hardly more than a day old (see the date and time of new Moon above) very low below Venus and Mercury while twilight is still bright, as shown above.

This Week's Planet Roundup

Mercury early this week emerges rapidly in the western twilight, far below Venus. On May 15th Mercury is still 13° beneath Venus and a bit to the right. But the gap between them closes by 2° per day until they come to conjunction on May 21st, 1° apart, as shown above. Thereafter they separate again, with Mercury now on top.

During the week Mercury fades from magnitude –1.1 to –0.6. Venus is 30 times brighter on their date of conjunction.

Venus (in northern Taurus) is dropping fast now! It shines brightly in the west-northwest in twilight, as it heads down toward its June 3rd conjunction with the Sun. Venus fades from magnitude –4.6 to –4.3 this week but remains a dazzler nonetheless.

A little farther above Venus each evening is Beta Tauri, magnitude 1.6. And Mercury climbs rapidly up from the horizon day by day to meet it.

In any telescope Venus is now quite the spectacle! It's a big, thin, brilliant crescent: enlarging from 49 to 54 arcseconds in diameter this week, bigger than any other planet ever appears, while slimming from 11% to just 5% sunlit. This is the best week to try to observe its crescent shape with binoculars or even your unaided eyes; see May 15 above.

Jupiter's Great Red Spot was on the planet's central meridian (System II longitude 331°) when Christopher Go took this image on May 5th in near-perfect seeing. South is up. "There are exceptional details resolved inside the GRS," he writes, and "the North Equatorial Belt is very chaotic."

Mars, Jupiter, and Saturn (magnitudes, +0.2, – 2.4, and +0.5, respectively) shine in the southeast to south before and during early dawn.

Jupiter, the brightest, is on the right. Before dawn begins, spot the Sagittarius Teapot off to the lower right of it.

Saturn glows pale yellow 4° to Jupiter's left. To me they look like an unequal pair of eyes looking down through the dawn.

Mars, in Aquarius, is much farther (30° to 35°) to Saturn's left as dawn begins. It has been slowly brightening and enlarging. In a telescope Mars is now about 8.5 arcseconds wide: a tiny gibbous disk. Mars is on its way to an excellent opposition in early October, when it will reach an apparent diameter of 22.6 arcseconds.

Mars on May 5th, imaged in excellent seeing by Christopher Go from the low latitude of Cebu City, Philippines, using video-frame stacking through a 14-inch scope. South is up. Don't expect anything like this visually! But even a much smaller scope should show Mars's gibbous shape and its currently huge South Polar Cap. We're looking here at the planet's Mare Cimmerium side. (The thin dark arc inside the lower limb is an imaging artifact.)

Uranus is hidden in the glow of dawn.

Neptune (magnitude 7.9, in Aquarius) is fairly low in the east-southeast just before dawn begins.

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.

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 here 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) or 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 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."

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.