The Sky This Week: Enjoy Venus and Mars in the evenings

Friday, May 5
The week kicks off with a stunning Full Flower Moon, the name for May’s Full Moon. Luna reaches Full phase at 1:34 P.M. EDT; this evening, observers in Africa, Asia, Australia, and New Zealand will enjoy a subtle penumbral lunar eclipse. This type of eclipse occurs when the Moon passes through the outer region of Earth’s shadow but never crosses into the darker central shadow. The moment of greatest eclipse occurs at 17:24 UTC, when eagle-eyed skywatchers may notice the northern limb looks a bit darker and duskier than the rest of the bright face.

The rest of the world won’t get an eclipse, but observers everywhere will get a stunning Full Moon lighting up the sky all night. Such a bright Moon can make deep-sky observing difficult — instead, focus on picking out some of the brightest constellations, particularly in the west, opposite the rising Moon. A few hours after sunset, Gemini the Twins are sinking toward the horizon, standing upright. The two bright stars that mark their heads, Castor and Pollux, shine at 1st magnitude and are relatively easy to spot. Look also for Mars — magnitude 1.4 — to the lower left (south-southwest) of Pollux, the orangey star on the left. Venus, much brighter than anything else in the region at magnitude –4.1, lies in far northeastern Taurus, above the two tips of the Bull’s horns, Alheka and Elnath.

Keep an eye on these two planets — we’ll revisit both later this week!

Other constellations you may spot include Leo and his famous Sickle asterism and Auriga with its bright luminary Capella. Also unmissable is Procyon in Canis Minor: This magnitude 0.4 star lies to the left (south) of Gemini.

Saturday, May 6
The Eta Aquariid meteor shower peaks today — unfortunately under a Full Moon! Because the Moon is up all night and sets after sunrise, shower meteors will be difficult to catch in the brighter sky.

Nonetheless, if the weather is mild and you’re up before the Sun, it’s worth a try. The shower’s radiant lies in the east, just above Saturn. The ringed planet serves as an excellent guidepost, so let’s check it out first.

Saturn is currently magnitude 0.9; it stands nearly 20° high an hour before sunrise. Look southeast to find it — you may still see the four bright stars that mark the Square of Pegasus asterism to the planet’s upper left. Far above it lies the Summer Triangle, pointing nearly straight up.

Through a telescope, Saturn’s disk is 16" and its rings a bit more than twice that span. If your observing site is at higher altitude and the air is particularly clear, you may notice the small moon Mimas is transiting the disk just south of the rings (depending on what time you look). The moon lies about midway on the planet’s face just before 5 A.M. CDT, after sunrise has already occurred for the East Coast. Mimas’ tiny dark shadow lies to its southwest, appearing to lead the moon across the disk. This observation will be challenging, but taking photos or video may reward you if your eyes can’t catch the show. Easier to see will be 8th-magnitude Titan, especially if you look earlier rather than later. The large moon lies some 2' due east of the planet.

In between glances at the Saturn, cast your eyes (without using a scope) to the left or right of the Eta Aquariids’ radiant in the sky. Looking away from this point gives you the highest chances of spotting shower meteors with longer trails.

Sunday, May 7
Look northeast around 10 P.M. local time tonight and you’ll find a bright point of light about 20° above the horizon. This is magnitude 0 Vega in Lyra, one of the points of the famous Summer Triangle. It’s also the first stop on our journey toward a stunning globular cluster in the next constellation over, Hercules.

From Vega, look west-southwest (to the star’s upper right) and you may notice a “box” of stars similar to the Great Square of Pegasus, only smaller. This is called the Keystone of Hercules. Some 16° from Vega is 3rd-magnitude Pi (π) Herculis. To its northwest is 3rd-magnitude Eta (η) Herculis. Continuing clockwise on the sky, you’ll find Zeta (ζ) Herculis and Epsilon (ϵ) Herculis, 3rd and 4th magnitudes, respectively.

We’re interested in the westernmost stars: Eta and Zeta. Draw a line between these two points and look about one-third of the way from Eta to Zeta with binoculars or a telescope. You’ll land on a large, softly glowing fuzzball composed of hundreds of thousands of stars. This is M13, the Hercules Globular Cluster.

At magnitude 5.8, this object can be visible to the naked eye on a perfect night, but the bright Moon tonight means some optical aid is definitely needed. M13 spans almost 20', so it’s quite large. Depending on your magnification, it may look completely fuzzy (at low power) or start to dissolve into many individual suns, particularly around the edges (under higher magnification).

There’s an added bonus here for photographers: Some 40' northeast of M13 is the 11th-magnitude galaxy NGC 6207. This target often shows up in images of M13, though if you get to it too late tonight, bright moonlight may thwart your efforts to capture it. That’s okay — just bookmark this entry and come back when the Moon has gone!

Monday, May 8
With the Moon rising later, there’s a widening dark window after sunset to begin enjoying faint objects once more. The western sky holds many targets for this week — remember Venus and Mars? We’re still coming back for them! But tonight, look a little higher above the horizon for Leo the Lion. His brightest star, Regulus, is still 50° high two hours after sunset.

We’re going to look a little higher still, moving east to locate the tip of the Lion’s tail, 2nd-magnitude Denebola. This is our anchor point for finding tonight’s two targets: the dwarf planet 1 Ceres and the spiral galaxy M99.

First, let’s locate Ceres. From Denebola, use binoculars or a telescope to scan just a little east. Eighth-magnitude Ceres lies within 2.5° of Denebola, to the star’s east-northeast. There aren’t many bright background stars here, so it should be a relatively easy ID, particularly with the chart at right. Ceres is drifting slowly, so you’ll need to come back every few nights to really catch any movement.

From the main-belt world, slide about 5° east-southeast this time (or just over 7° due east of Denebola). This will bring you to M99, a spiral galaxy in Coma Berenices. M99 is a face-on galaxy that shines at 10th magnitude, best seen with a telescope — particularly a larger aperture if you want to bring out some detail. Even in large instruments, however, its spiral arms are a bit hard to make out. Clearest is the southern arm, which is brighter than the others thanks to large clumps of star formation.

Tuesday, May 9
Uranus is in conjunction with the Sun at 4 P.M. EDT; it will reappear in the morning sky just before sunrise in late May, so we’ll make sure to catch this distant world once it’s visible again.

Very visible, though, is Venus. The bright planet still dominates the western sky after sunset and reaches its farthest declination north (26°) today, as well as its highest point above the ecliptic. Venus doesn’t set until nearly midnight for most of the U.S. and appears almost circumpolar from Alaska, remaining in the sky as both an evening and a morning star.

Venus now lies roughly due north of Eta Geminorum and hangs within 2° of the glittering open cluster M35, visible to the naked eye under good conditions at magnitude 5.3. The pair looks stunning in binoculars or a wide-field scope. Astrophotographers may want to take advantage of the juxtaposition.

Venus is now 63 percent lit and 18" across; its phase will shrink throughout the month to roughly half-lit by the end of May, while its angular size will grow to more than 20" at the same time.

Wednesday, May 10
Now let’s enjoy the other glorious evening planet: Mars passes 5° south of Pollux at 4 P.M. EDT. Catch it in this same position after sunset tonight, appearing to Pollux’s lower left. Mars sits 30° directly above Betelgeuse, the red giant that marks Orion’s shoulder, now sinking toward the horizon. The Red Planet shows off its small disk through a telescope, appearing just 5" wide, thanks to its vast distance from Earth. If we were to look down on the solar system from above, Earth is quickly pulling away from Mars as our planet’s faster orbital speed carries us around the Sun. Mars is about a quarter-orbit away after our planets came closest late last year.

While you’re enjoying this region of the western sky, take some time to enjoy the sight of both Pollux and nearby Castor through a telescope. Pollux is the cooler of the two stars, glowing orange-yellow. It is slightly cooler than the Sun, thanks to its more advanced age. Castor, which lies 4.5° northwest of Pollux, is a beautiful multiple star with two bright components separated by several arcseconds. Another member lies some 1.2' to their south. In truth, each of these three stars is also a binary, though optical instruments cannot split them further and their true nature was discovered spectroscopically.

Thursday, May 11
The Moon reaches perigee, the closest point to Earth in its orbit, at 1:05 A.M. EDT. At that time, our satellite will be 229,449 miles (369,262 kilometers) away.

Rising late in the evening in the southeast is the claw and upper body of Scorpius the Scorpion. His most noticeable feature is his bright red heart, Antares, a 1st-magnitude red giant whose hue is unmistakable. Center this star in your telescope, then move your field of view slowly northwest until Antares is just out of sight. Then, you might spot globular cluster NGC 6144, which lies less than 1° from the star. This 9th-magnitude cluster spans about 9' and is difficult to see when Antares is also visible, thanks to the star’s bright light.

An even easier-to-see globular also lies nearby: 7th-magnitude M80 is just 4.5° northwest of Antares. Slightly larger than NGC 1644 at 10', M80 is brighter and denser, its many hundreds of thousands of stars tightly packed. This increases its surface brightness, particularly toward the center. M80 is one of the densest globulars in our galaxy, and astronomers have found hints that collisions between stars in its central regions are common.

Friday, May 12
Last Quarter Moon occurs at 10:28 A.M. EDT. This phase of our Moon is visible well into the daytime, allowing anyone to observe it. If you do use binoculars or a telescope to do so, take extreme care never to point them anywhere near the region of the Sun, as even a quick glance at our star through optics can have lasting permanent damage for your eyesight.

The Moon now lies in Capricornus, leading Saturn through the sky. If you catch the scene in the few hours before sunrise, you can spot the large, bright moon Titan now due south of Saturn. The moon’s orbital period is 16 days, so it appears to move quickly — remember how it appeared east of the planet earlier this week as it rounded the curve at the far eastern extent of its path.

If you catch the planet before the sky grows too light, look also for the three 10th-magnitude moons Tethys, Dione, and Rhea. They stand in that order, from closest to farthest, in a rough line to Saturn’s east.