How much aperture does it take?
Seeing The Dumbbell Nebula through a telescope
A grey rectangle with the corners bitten out — the apple-core shape is obvious at 100 mm. Brighter and easier than its reputation suggests.
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
Recognisable
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 | 30 mm | 100 mm | 150 mm |
| Recognisable | 55 mm | 130 mm | 180 mm |
| Detailed | 175 mm | 250 mm | 300 mm |
When to look
Summer evenings in the northern hemisphere.