Messier 18 is a small, sparkling open cluster nestled in the rich star fields of Sagittarius, lying between the famous Swan Nebula (M17) and the brilliant Sagittarius Star Cloud. Although it is not as large or dense as some of its neighboring clusters, M18 has a charm all its own — a compact “pocketful of summer stars” that offers a pleasing view in binoculars and small telescopes. At about 4,600 light-years away, this cluster contains a few dozen stars that shine brightly against the Milky Way’s mottled background, making it a delightful target for observers exploring this busy region of sky.
What makes Messier 18 worth seeking out is its contrast. After looking at the sweeping grandeur of the Lagoon Nebula (M8), the star clouds around M24, or the bright nebulosity of Swan Nebula (M17), the tight little gathering of M18 feels almost like a secret treasure tucked between the giants. In binoculars, it looks like a small misty patch with a handful of resolved stars, while a small telescope transforms it into a cluster of glittering points. Larger instruments show that it is an irregular group, with bright stars scattered loosely, almost as if someone sprinkled stardust across the eyepiece.
M18 is also a fine stop on a summer star-hop of the celestial wonders of Sagittarius. Observing it in this way — as part of a chain of objects — gives a sense of the richness of the Milky Way in Sagittarius, where clusters and nebulae sit almost shoulder to shoulder.
M18
Rating: 🟢 Solid Catch
Level: 🔵 Easy
How:
When: Jun - Oct
🌟 Compact Beauty Amid Giants M18 is often overshadowed by nearby showpieces like the Lagoon (M8) and Swan Nebulae (M17), but its more modest appearance is part of its appeal. In small telescopes, it reveals itself as a compact, scattered grouping of stars — a simple and pretty contrast to the sweeping nebulae around it.
🌟 A Perfect Binocular Target At a magnitude of about 7.5 and spanning only 10 arcminutes, Messier 18 is ideally sized for binoculars. In dark skies, it appears as a misty little patch with a handful of resolved points, making it an accessible and rewarding object for casual stargazing sessions.
🌟 Easy to Find Along a Star-Hop Path Located between the Swan Nebula (M17) and the Sagittarius Star Cloud, M18 is perfectly placed on one of the richest celestial highways of the Milky Way. Observers can enjoy hopping from one bright nebula to another and pause at M18 as a stepping stone in this sequence of wonders.
🌟 Youthful Stellar Population M18 contains many young, blue stars that are only a few tens of millions of years old. For those who enjoy thinking about the life cycles of stars, this cluster represents a relatively recent chapter of stellar birth within our galaxy’s spiral arm.
Open cluster: a loose group of a few dozen to a few thousand young stars that formed together and are loosely bound by gravity.
M18
Find the Teapot asterism in Sagittarius low in the southern sky. If you need help, use the Summer Triangle and hop from Deneb to Altair (38°) and then hop again in the same direction and distance to the Teapot (38°).
Focus on the lid of the Teapot — the star Kaus Borealis (Lambda Sagittarii) is the topmost star. From Kaus Borealis, move 11° north/northeast along the Milky Way. Look for the constellation Scutum, which contains the star Gamma Scuti — a useful waypoint.
Using binoculars, a finder scope or a low-powered eyepiece, point to Gamma Scuti and then hop 2.5° to M17 looking for a bright nebula. Once found, hop south just under 1° to M18. In binoculars, it shows as a faint misty spot, while in a telescope its handful of bright stars stand out nicely against the rich Milky Way backdrop.
Bonus: Be sure to check out M17 (Swan Nebula) as well as the Sagittarius Star Cloud, just a degree further south.
M18
✅ Observe Under Dark Skies Like many clusters in Sagittarius, M18 is most rewarding away from light pollution. A dark background sky lets its stars sparkle more clearly, and the surrounding Milky Way glow enhances the view.
✅ Use Binoculars for a First Look M18 is small but bright enough to be seen with handheld binoculars under dark skies. It appears as a faint, misty patch, and spotting it this way adds to the fun of confirming it later with a telescope.
✅ Try a Small to Medium Telescope A telescope in the 3–8 inch range will resolve dozens of cluster stars. At moderate magnifications, M18’s loose, irregular shape stands out nicely against the dense star clouds of Sagittarius.
✅ Use Low to Moderate Power M18 is only about 10 arcminutes across, so low to medium magnification gives the best balance — enough power to resolve stars, but wide enough to frame the cluster against the rich Milky Way backdrop.
✅ Include It in a Star-Hop One way to find M18 is to sweep northward from the Lagoon Nebula (M8) toward the Sagittarius Star Cloud and then the Swan Nebula (M17). M18 sits between the Star Cloud and the Swan Nebula, making it a natural stop on a Milky Way tour.
M18
❌ Naked Eye
To the naked eye, Messier 18 is invisible under most skies. Even in very dark locations, it does not present itself as a distinct cluster, though its surrounding star fields and the nearby nebulae hint at the richness of the region where it resides.
✅ Binoculars
In binoculars, Messier 18 emerges as a faint, compact haze set against the busy backdrop of the Milky Way. Careful observation reveals a few scattered points of light within the haze, hinting at the youthful stars that make up the cluster.
✅ Small Telescope
Through a small telescope, Messier 18 takes shape as a loose sprinkling of a couple dozen stars. The stars are bright and somewhat irregularly arranged, giving the impression of a small family of suns tucked between two much larger celestial showpieces.
✅ Medium Telescope
A medium telescope provides a more satisfying view, resolving many more stars and revealing a range of magnitudes within the cluster. The young, blue-white stars contrast nicely with the Milky Way’s dense background, and the cluster appears more three-dimensional.
✅ Large Telescope
In a large telescope, Messier 18 is revealed in full detail, its stellar population spread across the field of view with fainter members brought into view. The increased resolution accentuates its irregular shape and provides a sense of its true nature as a youthful stellar gathering, modest in size but set within one of the most spectacular stretches of sky.
M18
Messier 18 is a modest open cluster that benefits greatly from darker skies. Its visibility and charm depend less on its brightness and more on how well it stands out from the Milky Way background.
🟣 In Bortle 1–2 skies, Messier 18 is a lovely compact patch of stars, clearly separated from the surrounding Milky Way glow. Its members sparkle vividly, and the whole cluster feels like a small jewel tucked among the richer nebulae nearby.
🔵 In Bortle 3–4 skies, the cluster remains distinct, though the surrounding Milky Way is not quite as striking. Messier 18 still shows well, with its handful of bright stars easily visible and a hint of its looser structure apparent.
🟢 In Bortle 5–6 skies, Messier 18 loses some of its context. The Milky Way background is muted, and while the cluster is still visible, it looks more like a small, sparse grouping of stars rather than a standout feature. Its contrast is diminished, though still recognizable with some effort.
🟠 In Bortle 7+ skies, Messier 18 is difficult to appreciate. The glow of light pollution erases most of the Milky Way and leaves the cluster as a few faint stars without cohesion. It can still be tracked down, but its beauty is largely lost in urban skies.
M18
DSOs within 48° or 2 outstretched hands at arm's length
M18 - A Pocketful of Summer Stars
Find the Teapot asterism in Sagittarius low in the southern sky. If you need help, use the Summer Triangle and hop from Deneb to Altair (38°) and then hop again in the same direction and distance to the Teapot (38°).
Focus on the lid of the Teapot — the star Kaus Borealis (Lambda Sagittarii) is the topmost star. From Kaus Borealis, move 11° north/northeast along the Milky Way. Look for the constellation Scutum, which contains the star Gamma Scuti — a useful waypoint.
Using binoculars, a finder scope or a low-powered eyepiece, point to Gamma Scuti and then hop 2.5° to M17 looking for a bright nebula. Once found, hop south just under 1° to M18. In binoculars, it shows as a faint misty spot, while in a telescope its handful of bright stars stand out nicely against the rich Milky Way backdrop.
