Resolution
Also called: Dawes limit, resolving power, Rayleigh limit.
The finest detail a telescope can show; the Dawes limit, 116 ÷ aperture in mm, is the closest equal double star it can split.
Light's wave nature blurs every star into a tiny airy disk. Bigger apertures make smaller disks: an 80 mm splits equal stars about 1.5″ apart, a 200 mm 0.6″, a 400 mm 0.3″ — when the seeing allows, which it often doesn't below about 1″.
In AstroPilot
Double-star pages compare each pair with your telescope's Dawes limit.