Messier 25 is a wide, loosely scattered open cluster set in the rich star fields of Sagittarius, about 2,000 light-years away. It contains around a hundred stars, several of which are bright enough to stand out clearly even in modest skies. With an apparent size close to a degree across, M25 is best enjoyed in binoculars or through a low-power telescope eyepiece, where its graceful arcs and chains of stars shimmer against the dense glow of the Milky Way.
One of the most convenient ways to find Messier 25 is to trace a line between two of Sagittarius’s best-known showpieces: the great globular cluster M22 and the bright Swan Nebula (M20). M25 lies about halfway between them, slightly offset to the east, making it easy to locate during a star-hopping session. Sweeping along this path not only brings you to M25, but also carries you through one of the richest stretches of the summer Milky Way.
What makes Messier 25 so charming is its openness. Unlike the tightly packed globular clusters nearby, M25 feels airy and relaxed, its members scattered like a handful of glitter tossed onto velvet. Adding to its interest is the variable star U Sagittarii, a Cepheid that pulses in brightness over days, providing a subtle reminder that the stars above are living, changing suns.
M25
Rating: 🟢 Solid Catch
Level: 🔵 Easy
How:
When: mid-Jun - Sep
🌟 Easy to Locate Between Giants One of the most appealing reasons to observe M25 is how easy it is to find. By sweeping between the great globular cluster M22 and the Swan Nebula (M20), you’ll come across M25 about halfway along the line. This placement between two of Sagittarius’s showpieces turns the cluster into a convenient stop on a rich summer star tour.
🌟 Expansive and Airy Appearance Unlike compact clusters that crowd their stars into a tight ball, Messier 25 is loose and open, with bright members spread gracefully across a wide area. Its scattered appearance makes it look like a sprinkling of jewels against the dark sky, giving it a relaxed charm that distinguishes it from its denser neighbors.
🌟 A Rich Stellar Family M25 contains roughly a hundred stars, including a mix of bright blue-white suns and fainter members that add depth to the cluster. The presence of the Cepheid variable U Sagittarii, whose pulsations subtly change its brightness over time, provides extra scientific interest for those who enjoy noticing subtle changes in the night sky.
🌟 Perfect for Wide-Field Instruments Because of its broad apparent size, Messier 25 is particularly rewarding in binoculars or with low-power eyepieces. This wide-field view frames the entire cluster in its stellar context, with the star fields of Sagittarius spilling across the background, creating a scene that feels immersive and rich.
🌟 A Contrast with Nearby Treasures Seen alongside the dense globular cluster M22 and the bright nebulosity of M20, Messier 25 provides a very different experience. Where the globular is tight and ancient, and the nebula is glowing and active, M25 feels light and spacious, offering a refreshing complement to its neighboring celestial wonders.
Open cluster: a loose group of a few dozen to a few thousand young stars that formed together and are loosely bound by gravity.
M25
M25 is conveniently located close to the halfway point between the globular cluster M22 and the Swan Nebula M17. Here's how to find it:
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 (+2.82) (Lambda Sagittarii) is the topmost star. From Kaus Borealis, look 11° north/northeast along the Milky Way to find the star Gamma Scuti (+4.69). Use binoculars if you need help in seeing it. M22 is close to Kaus Borealis while M17 is close to Gamma Scuti. Using a binocular or telescope finder, point to the halfway point between these two stars. With your binocular or a low-powered eyepiece, look for M25 as a graceful spray of stars, distinct from the smoother background of the Milky Way. Once found, you’ll see why it makes such a rewarding stop in this rich part of Sagittarius.
Bonus: Check out M22 (globular cluster) and M17 (Swan Nebula), both about 4° away on either side of M25.
M25
✅ Use Binoculars or Wide-Field Eyepieces Messier 25 is larger than the size of our Moon in the sky so it shines best with low magnification. Binoculars or wide-field eyepieces capture its full spread, letting you see its graceful chains of stars framed against the Milky Way.
✅ Seek Out Dark Skies Although some of M25’s brighter members can punch through light pollution, the cluster’s full richness only shows under darker skies. Away from city lights, dozens of fainter stars appear and the surrounding star fields glow with extra depth.
✅ Observe in Summer Evenings Sagittarius rides highest in the southern sky during summer months. Aim to view M25 in June, July, or August when it clears the horizon well after dusk, ensuring the best angle and sharpest view.
✅ Look for U Sagittarii If you enjoy subtle detail, focus on the Cepheid variable U Sagittarii within the cluster. Its brightness changes over several days, offering a chance to revisit M25 and notice differences over time.
✅ Frame It with Neighboring Wonders After enjoying M25, sweep the same region of Sagittarius for nearby showpieces like the rich globular M22 and nebulas including the Swan M20, Lagoon, and Trifid Nebulae. Observing M25 as part of this grand tour makes its wide scatter even more spectacular.
M25
❌ Naked Eye
To the naked eye, Messier 25 is generally not visible as a distinct object, even under very dark skies. At best, it subtly blends into the dense star fields of the Milky Way in Sagittarius, hinting at a brighter patch but offering no real detail.
✅ Binoculars
In binoculars, Messier 25 comes alive as a wide, loose grouping of bright stars. It appears with graceful chains and arcs of stars standing out against the surrounding Milky Way, making it an especially beautiful wide-field target.
✅ Small Telescope
Through a small telescope, the cluster reveals a richer texture. Dozens of stars resolve easily, and its airy, open structure becomes apparent, with no tight core but instead a pleasing scatter across the eyepiece. The variable star U Sagittarii may also be picked out as one of the brighter members.
✅ Medium Telescope
A medium telescope adds more depth, bringing fainter stars into view and enhancing the sense of the cluster’s true richness. The contrast between brighter suns and subtler companions creates a layered effect, showing Messier 25 as a cluster with both breadth and depth.
✅ Large Telescope
In a large telescope, Messier 25 appears as a glittering star field nearly overflowing the eyepiece. Numerous stars become visible, giving the cluster a three-dimensional quality, though its loose nature remains apparent. It feels less like a compact jewel box and more like a sparkling cloud embedded in the summer Milky Way.
M25
Messier 25 is a bright, wide open cluster in Sagittarius that benefits greatly from darker skies. Its loose structure and backdrop of the Milky Way make it more impressive when the sky itself is rich with starlight.
🟣 In Bortle 1–2 skies, M25 is a sparkling, expansive cluster filled with dozens of stars, clearly set against the glowing star fields of Sagittarius. Its wide scatter feels airy and brilliant, making it a standout feature in binoculars or low-power telescopes.
🔵 In Bortle 3–4 skies, the cluster remains striking, though the surrounding Milky Way is slightly muted. Its brighter members still shine prominently, and the cluster’s loose, graceful star chains are easy to pick out, though some of the faintest stars may fade.
🟢 In Bortle 5–6 skies, M25 loses much of its depth. The brightest stars remain visible, but the impression of richness is reduced and the surrounding Milky Way looks thin. The cluster is still pleasant, but it feels more like a sparse pattern of stars than a crowded open cluster.
🟠 In Bortle 7+ skies, M25 is difficult to appreciate. Only the brightest handful of stars can be seen, and its wide spread makes it easy to confuse with the background field. The cluster loses its sparkle and context, nearly disappearing into the urban glow.
M25
DSOs within 48° or 2 outstretched hands at arm's length
M25 - an Airy Cluster Lying between Giants
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 (+2.82) (Lambda Sagittarii) is the topmost star. From Kaus Borealis, look 11° north/northeast along the Milky Way to find the star Gamma Scuti (+4.69). Use binoculars if you need help in seeing it. M22 is close to Kaus Borealis while M17 is close to Gamma Scuti. Using a binocular or telescope finder, point to the halfway point between these two stars. With your binocular or a low-powered eyepiece, look for M25 as a graceful spray of stars, distinct from the smoother background of the Milky Way. Once found, you’ll see why it makes such a rewarding stop in this rich part of Sagittarius.
