M46
M46
Cluster · Pup
Set observing location to calculate altitude, timing and practical visibility. This guide describes the object in general.
What it looks like
M46 is a rich, fine-grained open cluster. Its stars tend to merge into haze in small optics; the small planetary nebula NGC 2438 projected against the field is a separate, harder target.
Detailed observing guide
General visual guidance · choose a method below. Check the calculated assessment for your actual conditions.
Why observe
The field combines a stellar population with an unrelated nebular view along the same sightline. For a simpler planetary-nebula comparison, explore M27.
Naked eye
M46 is not a reliable Naked eye target. A general brightening of the Puppis Milky Way does not identify the cluster.
Binoculars
Binoculars may show a misty patch under a dark sky, much less obviously stellar than neighbouring M47. Do not expect them to identify the projected planetary nebula reliably.
Telescope
A small telescope begins to resolve the cluster. Medium aperture reveals more of its fine stellar texture and may permit a careful NGC 2438 attempt; larger aperture gives more scope for the nebula’s disc. Keep the cluster in a wide field first, then use moderate power for the small separate nebular target.
Conditions and technique
Chart the Puppis field east of Sirius and distinguish M46 from brighter, coarser M47. Moonlight and sky glow suppress its many faint stars. Use averted vision and a clear view above horizon haze; identifying the field is not the same as detecting every object in it.
Filters
No nebula filter is recommended for the M46 star cluster. A separate OIII comparison may help isolate NGC 2438 while dimming the cluster; that is a test of the projected nebula, not an improvement to the stars.
Context and limits
NGC 2438 is not a bound member of M46: radial-velocity research rules out current membership. Their apparent overlap is a projection, so a photograph that places the nebula among the stars does not demonstrate a physical association.
Sources and editorial review
Reviewed 2026-10-03. Sources describe the object; visual advice is conservative editorial guidance, not a detection guarantee.