Special to CosmicTribune.com, May 19, 2025

Excerpts from weekly Sky&Telescope report.

MONDAY, MAY 19

■ The brightest asteroid, 4 Vesta, is nicely placed in a moonless dark sky in late evening. It’s about two weeks past opposition and still about magnitude 6.0. It’s located 24° below Arcturus, near the Virgo-Libra border, and about 9° and 10° above Beta and Alpha Librae, respectively.

If you have a really dark sky, can you detect Vesta with the unaided eye? It’s pretty much the only naked-eye dwarf planet, and only when near opposition.

TUESDAY, MAY 20

■ The last-quarter Moon (it’s exactly last-quarter at 7:59 a.m. EDT Wednesday morning) rises around 2 or 3 a.m. tonight. Upper left of it, by about two fists at arm’s length, the Great Square of Pegasus balances on one corner. The Square’s top right edge points down at the Moon.

Just before Wednesday’s dawn begins to make itself known, spot Saturn about a fist and a half to the Moon’s lower left. Continue farther lower left for almost the same distance, and that’s where Venus rises as dawn begins.

WEDNESDAY, MAY 21

■ With summer still 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. 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, less far to Vega’s lower left.

■ Early in dawn the next two mornings, the fickle Moon trades a dim partner for a bright one, as shown below.

The crescent/planet pairs two dawns in a row may be similar in form, but they’re very different in visibility. Don’t dawdle and let the sky get too bright!

THURSDAY, MAY 22

■ Have you ever seen even one star of Centaurus? Alpha Centauri, famous and bright, never gets above the horizon unless you’re as far south as San Antonio or Orlando (latitude 29° N). But Theta Centauri, shining at a respectable 2nd magnitude, makes it above your south horizon anywhere in the continental United States.

But you have to know where and when to look.

In late May, the time comes right after the end of twilight. And the place? Theta Centauri is almost three fists (27°) lower left of Spica, and just a bit farther (32°) lower right of Antares. You’ll need an open view very low there in the south; the farther north you are, the lower. Binoculars will help through light pollution near your south horizon, and/or if Theta Cen is so low that atmospheric extinction dims it a lot. Catch it and that’s one more constellation, or at least a piece of one, to add to your life list.

■ Do say hello to the waning crescent Moon over Venus early tomorrow morning, as shown above. They’ll be 6° or 7° apart for North America.

FRIDAY, MAY 23

■ Zero-magnitude Vega dominates the east-northeast these evenings. Look for its little constellation Lyra 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.

Most of the time Beta and Gamma are almost indistinguishable in brightness: Gamma is visual magnitude 3.25 and Beta is 3.4. But Beta is a famous eclipsing variable, one of the first discovered. Look up at those two enough times, and sooner or later you will catch Beta very obviously dimmer than Gamma, at its minimum brightness of mag 4.3. More often you’re likely to catch it somewhere in between, when the difference is clearly apparent but not as striking.

SATURDAY, MAY 24

■ 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 members form an inverted Y. The entire cluster is about 4° or 5° wide — a big, dim glow in a fairly dark sky. It nearly fills a binocular view.

SUNDAY, MAY 25

■ Bright Capella sets low in the northwest fairly soon after dark these evenings (depending on your latitude). That leaves Vega and Arcturus as the brightest stars in the evening sky. Vega shines in the east-northeast. Arcturus is very high toward the south.

A third of the way from Arcturus down to Vega look for semicircular Corona Borealis, with 2nd-magnitude Alphecca as its one moderately bright star.

Two thirds of the way from Arcturus to Vega is the dim Keystone of Hercules. It’s now lying almost level. Use binoculars or a telescope to examine the Keystone’s top edge. A third of the way from its left end to the right is 6th-magnitude M13, one of Hercules’s two great globular star clusters. In binoculars it’s a tiny glowing cotton ball. A 4- or 6-inch scope begins to resolve some of its speckliness. Located 22,000 light-years away far above the plane of the Milky Way, it consists of several hundred thousand stars in a swarm about 140 light-years wide.

  May 19-25: Saturn, The Sky, Venus rising at dawn’s light