How much aperture does it take?
Seeing The Ring Nebula through a telescope
A tiny grey smoke ring. Small enough that at low power you will pass over it without noticing; at 150× it is unmistakable and genuinely looks like a ring.
Through three telescopes, under a suburban sky
Each circle is the true field of a 10 mm eyepiece. Same target, same sky; only the aperture changes.
Not visible
Detectable
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 | 40 mm | 100 mm | 140 mm |
| Recognisable | 80 mm | 140 mm | 180 mm |
| Detailed | 180 mm | 240 mm | 280 mm |
What more aperture buys
The central star needs 400 mm and an exceptional night. Do not go looking for it in a 200 mm.
When to look
Summer evenings in the northern hemisphere.