Serpens the Serpent is unique among the constellations because it’s separated into two parts with Ophiuchus the Serpent-bearer between them. Serpens Caput (the head of the serpent) lies to the west of Ophiuchus, and Serpens Cauda (the tail of the serpent) lies to the east.
Serpens Caput is the larger of the two, taking up roughly 67 percent of the area. Together, they comprise the 23rd-largest constellation, which takes up about 1½ percent of the sky. But size doesn’t equal brightness. Of the 88 constellations, Serpens ranks 67th in that category. It lies opposite the Sun on June 6, so the two months before and after that date are the best times to view it.
Both parts contain deep-sky objects worthy of your attention. I started with the ones farthest west (in Serpens Caput) and moved eastward. So, if you start at the beginning, each subsequent object will come into view as the evening progresses.
In Serpens Caput
Our first target is globular cluster Palomar 5, one of 15 such objects discovered on Palomar Observatory Sky Survey plates and arranged into a list by American astronomer George Abell. Pal 5 glows softly at magnitude 11.8 and has a diameter of 7′. To find it, point your scope 9° west-northwest of magnitude 3.5 Mu (μ) Serpentis.
You’ll need at least an 11-inch scope to spot Pal 5 because of its low surface brightness. Start with a low-power eyepiece and increase the magnification up to about 100x. What you’re looking for is a round area just slightly brighter than the surrounding star field. Tapping on your telescope’s tube may help your eye to pick it out more easily.
If Palomar 5 is beyond your scope’s capability, our next target — another that’s the fifth on a list — will be a snap. It’s globular cluster M5, the brightest such object in the sky’s Northern Hemisphere. Sharp-eyed observers can spot it with their naked eyes from a dark site. If you try for it without optics, be sure not to confuse it with the 5th-magnitude star 5 Serpentis, which lies 22′ to the southeast. If you can see both objects, that’s a confirmed observation.
M5 glows at magnitude 5.7 and spans a worthy 17′. To locate it, first find Zubeneschamali (Beta [β] Librae). Then head about 11.5° north.
Even a 4-inch telescope will reveal lots of detail in M5. If sky conditions permit, increase the power to around 150x and examine the cluster. Does it appear grainy? At this magnification, the central region will resolve into several dozen stars.
If you can move up to an 11-inch scope, you’ll count more than a hundred stars. Note that the edges of the cluster contain lots of curves of stars that stand out nicely compared to the relatively sparse background.
Light from our next target, barred spiral galaxy NGC 5921, has traveled 75 million years to reach your telescope, so give it some respect. You’ll find it not quite 6° west-southwest of Unukalhai (Alpha [α] Serpentis). It glows at magnitude 10.8 and measures 4.9′ by 4.2′, which is slightly less than 3 percent of the area of the Full Moon.
Still, an 11-inch telescope on a moonless night of good seeing (atmospheric stability) should reveal the galaxy’s bright center, a faint oval ring that marks the extent of the arms, and perhaps its bar. The latter observation is a difficult one through medium-size scopes, so try high powers.
One more thing: Don’t think you’re seeing a supernova in NGC 5921. The magnitude 11.6 foreground star on the southwestern edge of the galaxy’s halo is always there.
Next up is the second-closest object on our list, double star Delta (δ) Serpentis, which lies some 230 light-years away. Actually, this is a quadruple star made of two binary star systems separated by a bit more than 1′. You’ll only see the brighter pair, however, because the fainter one has stars with magnitudes 14.7 and 15.2.
That brighter binary has stars with magnitudes 4.2 and 5.2, which are separated by 4″. Both stars appear light yellow. If you’re using a 4-inch telescope, use an eyepiece that magnifies around 100x and you should see this pair easily.
Ready for more galaxies? Specifically, are you ready to observe a flocculent galaxy? The arms of these objects appear like many small pieces all forming a spiral pattern. Such an object is a real contrast to a grand design spiral like the Whirlpool Galaxy (M51) in Canes Venatici.
The target you’re looking for is NGC 5962, which you’ll find about 2½° west-northwest of Beta Serpentis. It glows at magnitude 11.3 and measures 2.6′ by 1.8′. To be honest, an 11-inch scope is the minimum you’ll need to see details. At magnifications around 200x, NGC 5962 shows a broad central concentration. Unlike other galaxies with this feature, however, this one has a bright nucleus around 15″ across at its center.
Next up on our list is a galaxy group whose name gives away how many galaxies are in it: Seyfert’s Sextet. Sounds cool, right? Unfortunately, three of the galaxies are faint (magnitude 14.7 NGC 6027, magnitude 14.9 NGC 6027a, and magnitude 15.3 NGC 6027b) and the other three are really faint (magnitude 16.7 NGC 6027c, magnitude 16.4 NGC 6027d, and magnitude 16.7 NGC 6027e). To spot them, you’ll need at a dark night, great seeing, at least a 16-inch scope, and eyepieces to crank the magnification beyond 200x. Don’t try to see detail. Rather, make your goal just seeing all six members, and then check it off your astronomical bucket list.
The Sextet occupies an area of sky that measures only 2′ by 1′. To find it, point your scope 1.9° east of magnitude 4.7 Rho (ρ) Serpentis.
Once you’re done with Seyfert’s Sextet, aim your telescope 2.3° northeast of Delta Ophiuchi. There, you’ll find spiral galaxy NGC 6118. It glows at magnitude 12 and measures 4.7′ by 2.0′.
An 8-inch instrument will reveal a faint oval glow only slightly brighter than the background sky. Move up to a 14-inch scope, however, and if your night is one with good seeing, you should see this galaxy’s starlike core. Crank the power beyond 200x and a bit of spiral structure on the eastern end might also appear. Three foreground stars, all magnitude 14, are in our line of sight with NGC 6118.
In Serpens Cauda
Now pass through Ophiuchus and head to the eastern part of Serpens. The first target here is globular cluster NGC 6535. To locate it, point your scope 5.1° west-northwest of 3rd-magnitude Eta (η) Serpentis. Once you find it, you’ll quickly notice that you’re looking at an object similar to M5, but — at magnitude 10.6 — much fainter. It’s also much smaller, with a diameter of 3.6′.
On a dark, steady night, an 8-inch scope at magnifications above 200x will show a mottled sphere. Keep cranking the power up and you may detect that the outer edge isn’t a continuous circle. But you’ll need a much larger scope to resolve that region into stars.
Next on our list is another globular cluster, NGC 6539. Unfortunately, it glows softly half a magnitude fainter than NGC 6535, at magnitude 9.6. It does appear twice as large, however, 6.9′ across.
Look for it 0.7° northeast of Tau (τ) Ophiuchi, a reasonably nondescript 5th-magnitude star. NGC 6539’s brightest stars register at a paltry 16th magnitude, so you won’t resolve them. Through an 11-inch scope at high powers (300x and above), you might detect some graininess across the face of the cluster.
Our next target is a two-for-one because it combines an open cluster and an emission nebula. Through telescopes up to 8 inches in aperture, you’ll mainly see the open cluster, NGC 6604. It glows at magnitude 6.5 and measures 4′ across. Actually, its small size makes it stand out well against the background.
Larger scopes will let you count about 25 stars and reveal the emission nebula as a faint haze around them. If you want to accentuate the nebula, screwing a nebula filter into your eyepiece will dim the stars. To find NGC 6604, point your scope 3.6° northwest of Gamma (γ) Scuti, the only reasonably bright (well, magnitude 4.7) star in the area.
Another open cluster, NGC 6605, is next, and like NGC 6604, it, too, can be found by starting at Gamma Scuti. For this object, however, just head a bit more than 3° west of the star. At magnitude 6.0 and with a diameter of 7′, NGC 6605 can theoretically be seen by sharp-eyed observers without optical aid – but the surrounding star field is crowded with faint stars, so it’s tough.
Even a 4-inch scope will show only a slight brightening in this area. Yes, that’s the cluster. Step up to an 11-inch scope, however, and you’ll be able to see some 75 of NGC 6605’s stars.
Many observers think that our next object, the Eagle Nebula (M16), is in Sagittarius, probably because that constellation contains so many Messier objects. M16, however, lies just to the north of the Archer. To locate it, point your scope about 2½° west-northwest of Gamma Scuti. Or, if you need a brighter star to start from, head a bit more than 6° southeast of Nu (ν) Ophiuchi.
Because of its common name, it’s easy to think of this object as a nebula. Actually, it’s a combination of a nebula and an open cluster, and the latter — NGC 6611 — is much easier to see. The cluster glows at magnitude 6.0 and measures 21′ across. The emission nebula, IC 4703, surrounds the cluster and stretches a bit to the south.
Within the Eagle Nebula is a feature dubbed the Pillars of Creation, made famous by a Hubble Space Telescope image created by American astronomers Jeff Hester and Paul Scowen. Seeing them isn’t a difficult observation (many observers have, including me) if you’re able to use a 14-inch or larger telescope on a moonless night of great seeing.
Next up is our list’s only solo Index Catalogue object, IC 4756, commonly known as Graff’s Cluster. The IC is actually two supplements to the New General Catalogue. IC 4756 is also somewhat rare for an IC object in that sharp-eyed observers can spot it with their naked eyes.
You’ll find this open cluster roughly 4½° west-northwest of Alya (Theta [θ] Serpentis). Graff’s Cluster glows at magnitude 5.0, measures 52′ across, and looks like a tiny bright part of the Milky Way that’s broken off from the main stream.
A 4-inch scope with an eyepiece that provides a field of view of 1° will reveal some 50 stars. The one star that will stand out lies at the cluster’s southeastern edge. It glows at magnitude 6.4 and contributes a lot to IC 4756’s overall brightness.
Our final target, at a distance of 162 light-years, is also the closest one on our list: the double star Alya (Theta Serpentis). It may not be immediately obvious to you because its two components glow at magnitudes 4.5 and 5.4. Amateur astronomers usually start at Delta Aquilae, which glows at magnitude 3.4, and move a bit more than 7° to the west.
The two stars of Alya are separated by 22.3″, which makes them an easy split through a 4-inch scope at 100x. And while it’s true that colors are subjective, most observers see the brighter component as blue and its companion as pale yellow.
I hope you’ll take some time on a clear moonless summer night to observe these sweet treats in both parts of Serpens. Good luck!
