Messier 39 is a bright, loosely arranged open star cluster located in the constellation Cygnus, about 800 light-years from Earth. Shining at magnitude 4.6 and spanning nearly 30 arcminutes—roughly the size of the full Moon—it’s an ideal target for binoculars and small telescopes, especially in late summer and autumn.
What makes M39 especially appealing is its simple yet striking triangular shape, formed by about two dozen moderately bright stars. The cluster is open and airy, with generous spacing between stars, giving it a delicate appearance that contrasts nicely with denser clusters like M11 or M37. Some of the stars in M39 show subtle color differences, including hints of yellow and blue, which add visual interest to the view.
Located near the tail of Cygnus the Swan and easily found under dark skies, M39 is a relaxing, elegant target. It doesn’t demand large aperture or perfect conditions—just a clear sky and a wide field of view to enjoy its crisp, geometric arrangement of stars. It’s a quiet gem that invites a slower, more contemplative look at the richness of our galactic neighborhood.
M39
Rating: 🔵 Stagazer Favorite
Level: 🟢 Moderate
How:
When: Jul - Dec
🌟 A Bright, Easy Target for Any Skill Level At magnitude 4.6, M39 is visible to the naked eye under dark skies and easily seen through binoculars even in light-polluted areas. Its brightness and large size make it an excellent object for beginners or for quick, satisfying views with minimal equipment.
🌟 Beautiful in Binoculars and Wide-Field Scopes M39’s loosely spaced stars are ideally framed in binoculars or a telescope with a wide field of view. The cluster’s spread-out pattern and generous star spacing make it a relaxed and comfortable object to observe without crowding the field.
🌟 A Unique and Recognizable Shape The triangular or wedge-like arrangement of stars gives M39 a clear and memorable structure. The simplicity of its pattern makes it easy to identify and enjoyable to revisit, especially for observers who enjoy spotting visual patterns in the sky.
🌟 Subtle Color Contrasts in the Stars Several stars in M39 display subtle hints of blue or yellow, especially in larger apertures or with good seeing conditions. These color differences add visual interest and make it a good cluster for observers looking to develop color perception skills at the eyepiece.
🌟 Conveniently Located in Cygnus M39 is situated in the rich constellation of Cygnus, near the Swan’s tail, and is moderately easy to find using bright stars like Deneb as a guide. Its position makes it a natural stop during a night of observing the Milky Way, particularly in the late summer sky.
🌟 A Peaceful Alternative to Denser Clusters/b> Unlike compact open clusters such as M11 or M37, M39 offers a more relaxed experience. Its wide spacing and lower star count provide a different flavor of deep-sky observing—ideal for quiet contemplation or casual stargazing.
Open cluster: a loose group of a few dozen to a few thousand young stars that formed together and are loosely bound by gravity.
M39
Find the bright star Deneb (+1.33) in Cygnus. Cygnus, Vega and Altair are the three stars that form the Summer Triangle.
Try to find three much dimmer stars: Xi Cygni (+3.71), Rho Cygni (+3.99) and Pi2 Cygni (+4.25). These are all about 5° apart. If your skies are Bortle 5 or better, these should be easy to spot.
Choose Option 1 below if you can see the three stars. Otherwise choose Option 2. Or, if you prefer a challenge, choose Option 2.
Option 1: Using binoculars or finder, point to the halfway point between Rho and Pi2 Cygni. Then hop to M39.
Option 2: With binoculars, a finder or a low-powered eyepiece, point to Deneb. Then hop to Xi, Rho, and Pi2 Cygni. Backup halfway to Rho Cygni and hop to M39.
Messier 39 will appear as a wide scattering of stars in a rough wedge or triangle shape, with a few brighter stars standing out immediately. Explore using higher power.
M39
✅ Use Low Power and a Wide Field Messier 39 spans about 30 arcminutes, so a low-power eyepiece or binoculars will frame it best. Its stars are widely spaced, and too much magnification can push them out of view or make the pattern harder to appreciate.
✅ Scan from Deneb in Cygnus Start at Deneb, the tail of the Swan in Cygnus, and sweep northeast. M39 lies about 9° from Deneb and shows up easily in binoculars as a loose patch of stars against the Milky Way’s glow.
✅ Observe Under Dark Skies for Contrast Although M39 is bright, dark skies help separate its stars from the busy background of the Milky Way. A darker sky brings out the cluster’s triangular shape and enhances subtle color differences between stars.
✅ Try Averted Vision for Fainter Members Looking slightly to the side of the cluster can help reveal dimmer stars in the outer regions. Averted vision makes the field feel richer, even in modest apertures.
✅ Take Time to Trace Patterns The stars of M39 form graceful arcs and loose triangles. Take time to sketch or mentally trace the layout—it’s a great way to train your eye and enjoy this bright, open cluster more deeply.
✅ Compare with Nearby Clusters After observing M39, check out nearby open clusters like M29 or NGC 7082. Comparing shapes, star density, and structure deepens appreciation for the variety among Milky Way clusters.
M39
⚠️ Naked Eye
With the naked eye under dark skies, Messier 39 may appear as a faint patch or subtle brightening in the Milky Way, though it is not easily resolved into individual stars. Its wide, loose structure makes it difficult to distinguish without optical aid, but attentive observers may notice it as a diffuse glow northeast of Deneb in Cygnus.
✅ Binoculars
In binoculars, M39 becomes an appealing cluster of stars. Its triangular shape and loose pattern are clearly visible, with about two dozen moderately bright stars forming graceful lines and arcs. The stars are well-separated, making the cluster easy to observe even with handheld optics, and the surrounding Milky Way adds richness to the background.
✅ Small Telescope
Through a small telescope, the stars of M39 appear sharper and more vibrant. The open layout fills the field nicely at low power, and the individual stars are bright enough to stand out clearly. The triangular or wedge-like shape becomes more defined, and subtle variations in brightness and color may be noticed among the stars.
✅ Medium Telescope
With a medium telescope, M39 gains a sense of depth. More faint stars appear between the brighter members, and the field becomes more textured without becoming crowded. Color contrasts between bluish and yellowish stars become more pronounced, and the cluster’s overall structure is still easily appreciated at low to moderate magnification.
✅ Large Telescope
In a large telescope, M39 remains spacious and serene. While the field resolves into even more stars, the cluster retains its open feel. The brighter stars show strong color and clarity, and the added resolution reveals faint companions and subtle pairings that enhance the triangular form. Despite the aperture, the best view still comes at lower magnification, where the entire cluster can be framed and enjoyed in full.
M39
Messier 39 is best viewed under dark skies, where its bright, widely spaced stars stand out cleanly and its triangular shape is most apparent. It remains observable in moderate light pollution, but much of its elegance fades in urban conditions.
🟣 In Bortle 1–2 skies, Messier 39 is a beautiful and distinct open cluster. Its bright stars stand out crisply against the dark background, and the triangular shape is clear and well-defined. The surrounding Milky Way enhances the view, adding depth and context.
🔵 Under Bortle 3–4 skies, M39 still appears bright and attractive. Most of its stars remain visible, and the cluster’s shape is easy to trace, though the richness of the background star field begins to fade slightly.
🟢 In Bortle 5–6 conditions, M39 remains visible but loses some of its charm. The brightest stars still show clearly, but the fainter ones begin to blend into the brighter sky. The triangular pattern is still detectable, but the overall field looks more sparse.
🟡
Under Bortle 7+ skies, M39 is reduced to just a few scattered stars. The cluster’s shape becomes difficult to recognize, and the surrounding skyglow diminishes the contrast needed to appreciate its structure.
M39
DSOs within 48° or 2 outstretched hands at arm's length
M39 - a Sparkling Triangle in the Northern Sky
Find the bright star Deneb (+1.33) in Cygnus. Cygnus, Vega and Altair are the three stars that form the Summer Triangle.
Try to find three much dimmer stars: Xi Cygni (+3.71), Rho Cygni (+3.99) and Pi2 Cygni (+4.25). These are all about 5° apart. If your skies are Bortle 5 or better, these should be easy to spot.
Choose Option 1 below if you can see the three stars. Otherwise choose Option 2. Or, if you prefer a challenge, choose Option 2.
