Comet SWAN punking out? (Updated May 13.) Comet SWAN (C/2020 F8), now low above the pre-dawn horizon for mid-northern observers, has stalled out at about magnitude 5.5 rather than brightening to 3rd as hoped. It's low above the pre-dawn northeast horizon (for observers at mid-northern latitudes) this week and next, then its best visibility will shift to low above the northwest horizon right after dusk as it approaches its May 27th perihelion. In other words, low and tricky to find! It crosses Perseus for the rest of May. See Bob King's Comet SWAN charts. You'll need big binoculars or a telescope.
Supernova in Leo, magnitude 12.4. (Updated May 13.) A supernova in visual range of 6-inch scopes has erupted in NGC 3643 south of the hind foot of Leo, high after dark. As of May 12th, SN 2020hvf was about magnitude 12.4 and easily outshining its host galaxy. Meanwhile, a deeper challenge is 14.4-magnitude SN 2020jfo in M61 in Virgo, also high these evenings. See Supernovae Light Up in M61 and NGC 3643.
Friday, May 8
■ All week, look high in the west at nightfall for Pollux and Castor, the heads of the Gemini twins. They're lined up almost horizontally (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. To their lower left 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.
■ The waning gibbous Moon rises in the east-southeast tonight around 10 p.m. daylight-saving time, depending on where you live in your time zone. Once it's well up, look to its right or lower right for Antares, twinkling pale orange. Around and to the upper right of Antares are lesser, whiter stars of Scorpius.
Saturday, May 9
■ The Summer Triangle is making its appearance in the east, one star after another. The first in view is bright Vega. It's already visible in the northeast as twilight fades.
Next up is Deneb, lower left of Vega by two or three fists at arm's length. Deneb takes about an hour to appear after Vega does, depending on your latitude.
The third is Altair, which shows up far to their lower right by midnight.
■ Asteroid to occult a star. David Dunham of the International Occultation Timing Association writes us, "Occultation of 9.5-magnitude SAO 82820 by (667) Denise [along a track from] northern Mid-Atlantic (clear skies forecast there) to southern Oregon, night of Saturday May 9/10; see page for this event. The path passes over Washington, DC (4:54 UT May 10 UT); Columbus & Dayton, OH (4:55 UT); Indianapolis and Urbana, IL (4:56 UT); Des Moines and Omaha (4:57 UT); and Pocatello and Twin Falls, Idaho (5:00 UT)."
Sunday, May 10
■ Three zero-magnitude stars shine after dark in May: Arcturus high in the southeast, Vega much lower in the northeast, and Capella in the northwest (upper right of Venus). They appear so bright because each is at least 60 times as luminous as the Sun, and because they're all relatively nearby: 37, 25, and 42 light-years away, respectively.
■ Another asteroid occultation. David Dunham writes, "Occultation of 5.7-magnitude 14 Cancri by (363) Padua for the southwestern US Sunday evening, May 10/11; see the IOTA page for the event, with a lot of observing advice."
■ Before dawn on Monday the 11th, the waning gibbous Moon shines in the south. Left of it are Jupiter and Saturn, as shown below.
Look closer below the Moon for the handle of the Sagittarius Teapot. The handle's three brightest stars show at far right in the scene below.
Monday, May 11
■ Before and during early dawn on Tuesday the 12th, the waning gibbous Moon shines under Jupiter and Saturn as shown above. For skywatchers in North America's Central and Mountain time zones, they'll form a virtually perfect right triangle while dawn is brightening.
Tuesday, May 12
■ Vega is well up in the east-northeast as evening advances. Look for its faint little constellation Lyra, the Lyre, hanging down from Vega with its two-star bottom canted a bit to the right.
■ Take advantage of these moonless evenings to work through a fine clutch of galaxies in the northern reaches of the Virgo Cluster high overhead, using the Deep-Sky Wonders article and charts in the May Sky & Telescope, page 54. The five selections there range from magnitude 9.6 to 12.8.
Wednesday, May 13
■ This is the time of year when Leo the Lion starts walking downward toward the west, on his way to departing into the sunset in early summer. Right after dark, spot the brightest star fairly high in the west-southwest. That's Regulus, his forefoot.
■ Before and during early dawn Thursday and Friday, the waning Moon accompanies Mars as shown above.
Thursday, May 14
■ A gigantic asterism you may not know about is the Diamond of Virgo, some 50° tall and extending over five constellations. It now stands upright in the south after dark. Start with Spica, its bottom. Upper left from Spica is bright Arcturus. Almost as far upper right from Arcturus is fainter Cor Caroli, 3rd magnitude. The same distance lower right from there is Denebola, the 2nd-magnitude tail-tip of Leo. And then back to Spica.
The bottom three of these stars, the brightest, form a nearly perfect equilateral triangle. Maybe we should call this the "Spring Triangle" to parallel those of summer and winter?
■ Last-quarter Moon (exact at 10:03 a.m. Eastern Daylight Time). Tonight the Moon rises very late, around 3 a.m. Friday morning daylight-saving time, by which time it will be visibly a little past first quarter, as shown above. And Mars will be upper right of it.
Friday, May 15
■ A naked-eye Venus challenge! All week, the large, thin crescent shape of Venus is easy to discern with even a very small telescope or good, steadily braced binoculars. But can you resolve its 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 is too dark and Venus's glare becomes overwhelming. Look long and carefully and report your results to Sky & Telescope's Bob King, email@example.com, as told in the May issue, page 49.
You may improve your chances by sighting through a clean, round hole in a stiff piece of paper 1 mm or 2 mm in diameter (try both). This will mask out optical aberrations that are common away from the center 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). Before dawn, a bereaved lover roams an October woodland "with Psyche, my soul." Ahead of them low in the east, where Leo always ascends 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 Roman Venus-goddess:
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, less dazzling 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 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 – perhaps in Poe's "lair of the Lion," the sky area from which the traditional Leo figure stalks away.
Venus was also there in the mid- and late "lonesome October" of that year as a larger, thinner crescent, but the Moon was not.
Saturday, May 16
■ 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. It's upper right of Procyon, the brightest star due west, by about a fist and a half. The brightest star of Hydra 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. Hydra's star pattern, from forehead to tail-tip, is 95° from end to end, longer than any other constellation.
This Week's Planet Roundup
Mercury begins to creep up into evening twilight late this week. Start looking for it around May 13th, very low in the west-northwest 20 or 30 minutes after sunset. It's roughly 15° lower right of Venus. Binoculars help. At least Mercury is brighter than usual at magnitude –1.2. It gets a little higher and easier each evening. Mercury will pair up with Venus on May 21st, when they'll be 1° apart.
Venus (magnitude –4.7, in northern Taurus) is the bright white "Evening Star" in the west during and after dusk. It's still at its brightest but is moving lower day by day.
Look upper right of Venus for Capella, almost two fists at arm's length (18°) away. Much closer above Venus is Beta Tauri (El Nath), fainter at magnitude 1.6. They're within 2° of each other all week.
Mars, Jupiter, and Saturn (magnitudes, +0.3, – 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 to the right of it.
Saturn glows pale yellow 4° to Jupiter's left. To me they look like an unequal pair of eyes in the dawn.
Mars is much farther (25° or 30°) to Saturn's left or lower left. In a telescope Mars has grown to 8 arcseconds wide: no longer a tiny blob but a little 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.
Uranus is hidden low 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.
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.
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.