How much aperture does it take?
Seeing The Pleiades through a telescope
Six or seven blue-white stars to the naked eye, dozens in binoculars. Too big for most telescopes to frame — this is a target where more aperture actively makes things worse.
Through three telescopes, under a suburban sky
Each circle is the true field of a 25 mm eyepiece. Same target, same sky; only the aperture changes.
Detailed
Detailed
Detailed
The aperture it takes, by sky
Millimetres of aperture to reach each level. Observing heuristics, quoted at Bortle 4 and adjusted per class of sky — somebody else's eyes, somebody else's night.
| Level | Milky Way blazing | Milky Way, barely | No Milky Way |
|---|---|---|---|
| Detectable | 1 mm | 21 mm | 41 mm |
| Recognisable | 6 mm | 30 mm | 50 mm |
| Detailed | 40 mm | 70 mm | 90 mm |
What more aperture buys
The nebulosity around the stars is real but very faint, and needs a dark sky and a wide field rather than aperture.
When to look
Winter evenings in the northern hemisphere.