NGC 2451 (Open Clusters)
Two open clusters in Puppis that line up on the sky but lie at different distances: NGC 2451A about 620 light-years away and NGC 2451B about 1,200. Together they make a bright naked-eye patch.
Open cluster in Puppis. Magnitude 3.2.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 45° above the southern horizon at its highest; from Lethem (3.4° N), to 49° above the southern horizon. It is highest at midnight on the night of 14 Jan, in the middle of its season. The page works out tonight's rise, highest point and set for both towns in Guyana time (UTC-4), and where the Moon is.
What you'll see
- Your eyes: Visible to the eye even from Georgetown, as a hazy knot of stars. It lies 4.1° north-west of Naos.
- 10x50 binoculars: Resolves into dozens of stars. NGC 2477 is 1.5° away.
- A small telescope (80 to 100 mm): Too big for high power: a scatter of bright stars at the lowest power; NGC 2477 is 1.5° away.
- A camera: Spans about 40% of an APS-C frame at 800 mm (field 1.7° × 1.1°); needs a tracking mount.
How big, how bright, how far
- Size on the sky: 37.5′, 1.2 Moons across (the Moon is about 31′ wide).
- Brightness: magnitude 3.2. Brighter than the faintest stars Georgetown shows (4.3), and Lethem's (6.0).
- Distance: Between about 620 and 1,200 light-years. The light reaching your eye left it between about 620 and 1,200 years ago.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Two open clusters in one direction
- Notable
- NGC 2451A: about 220 Suns, 26 million years old, at 620 light-years; NGC 2451B: about 490 Suns, 28 million years old, at 1,200 light-years.
What is in it, not measured:
- Stars born together: from one cloud of gas, at one time
- Hot blue stars: still shining, because the cluster is young
How we know: Distance from Gaia parallaxes of the stars of its two clusters: Hunt & Reffert 2024, A&A 686, A42 (Gaia DR3 cluster catalogue, VizieR J/A+A/686/A42), retrieved 2026-10-21: NGC 2451A 190 pc and NGC 2451B 368 pc, two clusters in one direction. True size: Two clusters at different distances: no single size, two open clusters in one direction, not one object; Hunt & Reffert 2024 distances, see distance.
More deep-sky objects: NGC 2477 (Open Cluster) · NGC 2467 (Nebula and Cluster) · NGC 2547 (Open Cluster) · M93 (Open Cluster) · NGC 2362 (Open Cluster) · IC 2395 (Open Cluster)