The Alpha Persei Cluster, also known as Melotte 20, is a sprawling, majestic open cluster surrounding the bright star Mirfak in the constellation Perseus. Visible to the naked eye under dark skies, it stretches across several degrees and is truly spectacular in binoculars or a wide-field telescope.
What makes Melotte 20 so enticing is its scale and sparkle. Dozens of young, blue-white stars appear scattered like frost across the sky, many of them loosely gathered around Mirfak. There’s a sense of depth and flow in the pattern—this isn’t a tight knot like the Pleiades, but a rich, drifting field that seems to shimmer across the constellation.
It’s also an ideal object for casual observing: no filters needed, no hunting or dark adaptation required. Just point your binoculars or low-power scope toward Perseus on a crisp fall or winter night, and you’ll be rewarded with a grand stellar vista. The Alpha Persei Cluster is one of the sky’s hidden treasures—bright, accessible, and a joy to explore.
Alpha Persei Cluster
Rating: 🔵 Stagazer Favorite
Level: 🟣 Very Easy
How:
When: Oct - Mar
🌟 Visible with the Naked Eye Even from semi-dark skies, the Alpha Persei Cluster is visible as a soft glow around Mirfak. It’s one of the few deep-sky objects that needs no equipment to appreciate, making it ideal for casual stargazing and beginner observers.
🌟 Perfect for Binoculars and Wide Fields Unlike compact clusters, Melotte 20 spans several degrees and shines best through binoculars or low-power telescopes. Its scattered, shimmering stars fill the field of view and create a sense of openness and depth.
🌟 Bright and Youthful Stars The cluster is rich in young, hot, blue-white stars, which give it a distinct sparkle. These stars are still relatively close to their birthplace and offer a vivid example of a stellar association in progress.
🌟 Beautifully Positioned in Perseus Centered around Mirfak, the Alpha Persei Cluster is easy to locate and well placed in autumn and winter skies. It also lies near several other interesting targets, making it a great launch point for exploring the Perseus region.
🌟 Excellent for Teaching and Sharing Because it’s so bright, large, and easily found, this cluster is a favorite for public star parties and outreach. It shows well even in light-polluted skies and is a natural way to introduce others to the beauty of star clusters.
🌟 A True Sky Vista Melotte 20 isn’t just a cluster—it’s a celestial landscape. Its loose structure and wide spread give it the feel of a stellar river, gently flowing through the Milky Way, making it as visually relaxing as it is impressive.
Open cluster: a loose group of a few dozen to a few thousand young stars that formed together and are loosely bound by gravity.
Alpha Persei Cluster
Star hopping to the Alpha Persei Cluster (Melotte 20) is wonderfully easy—it’s one of the rare deep-sky objects that’s centered on a bright naked-eye star, Mirfak (Alpha Persei), making it almost effortless to find. In this step, find bright Mirfak (+1.80)either hopping from the Great Square of Pegasus or below Cassiopeia.
Point your eyes, binoculars or telescope to Mirfak so that it is centered. Slowly pan around Mirfak. The Alpha Persei Cluster fills a wide field, with stars of similar brightness gently flowing outward in all directions, creating a shimmering stellar backdrop.
Alpha Persei Cluster
✅ Use Binoculars or a Wide-Field Scope This cluster spans several degrees, so binoculars or a low-power telescope with a wide field of view give the best experience. Higher magnifications will cut off much of its graceful sprawl.
✅ Center on Mirfak Start with Mirfak (Alpha Persei) in the center of your view. From there, the rest of the cluster radiates outward, forming a loose, glittering pattern of bright stars.
✅ Observe from a Dark Location Though visible from suburban skies, a dark site reveals more stars within the cluster and enhances the contrast between bright and faint members, deepening the effect.
✅ Take Your Time Scanning Pan slowly through the region. The cluster doesn’t have a sharp boundary, and its charm lies in the gradual, sweeping arrangement of stars across the field.
✅ View It in Autumn or Winter Alpha Persei rides high in the evening sky from October through February/March. Observe when it’s near its highest point to avoid atmospheric distortion and enhance clarity.
✅ Include It in a Constellation Tour Pair it with nearby objects like the Double Cluster or Algol for a richer observing session. The Perseus region is full of interesting stars and deep-sky gems.
Alpha Persei Cluster
✅ Naked Eye
With the naked eye, the Alpha Persei Cluster appears as a subtle hazy glow around the bright star Mirfak, especially noticeable under dark skies.
✅ Binoculars
In binoculars, the cluster transforms into a wide, dazzling field of blue-white stars scattered loosely across several degrees, with Mirfak shining prominently at the center.
✅ Small Telescope
A small telescope at low power reveals even more members, offering a richly textured star field that still maintains its airy, sprawling structure.
✅ Medium Telescope
Through a medium telescope, the field tightens and begins to lose some of its visual breadth, though fainter stars come into view.
⚠️ Large Telescope
In a large telescope, the cluster becomes too wide for the field of view to fully contain; you see sharp detail in individual stars, but much of its graceful sweep is lost, making wide-field instruments the best way to appreciate its true beauty.
Alpha Persei Cluster
The Alpha Persei Cluster is resilient to light pollution thanks to its bright stars, but its full beauty—its scale, richness, and glow—comes alive under Bortle 1–4 skies, especially when viewed with binoculars or a wide-field scope.
🟣 In Bortle 1–2 skies, the Alpha Persei Cluster is a striking naked-eye feature, appearing as a shimmering patch surrounding Mirfak. Its many bright members stand out clearly, and the full sweep of the cluster is vivid and rich with contrast.
🔵 In Bortle 3–4 skies, the cluster remains bold and attractive. Its brightest stars are still prominent, though the background darkens slightly, making the surrounding fainter members less apparent without optics.
🟢 In Bortle 5–6 skies, the cluster loses some of its subtlety to skyglow. The central stars near Mirfak remain visible, but the outer reaches fade, and the sense of scale diminishes without optical aid.
🟡 In Bortle 7+ skies, light pollution significantly washes out the cluster. Mirfak is still bright, but only a few surrounding stars are visible to the unaided eye. The full extent of the cluster requires binoculars to appreciate.
Alpha Persei Cluster
DSOs within 48° or 2 outstretched hands at arm's length
Alpha Persei Cluster - the Crown of Perseus
Star hopping to the Alpha Persei Cluster (Melotte 20) is wonderfully easy—it’s one of the rare deep-sky objects that’s centered on a bright naked-eye star, Mirfak (Alpha Persei), making it almost effortless to find. In this step, find bright Mirfak (+1.80)either hopping from the Great Square of Pegasus or below Cassiopeia.
Point your eyes, binoculars or telescope to Mirfak so that it is centered. Slowly pan around Mirfak. The Alpha Persei Cluster fills a wide field, with stars of similar brightness gently flowing outward in all directions, creating a shimmering stellar backdrop.
