Resolvo

Meet Resolvo, a round lens who can just tell two close stars apart, and wants to be bigger so he can see more.

Light passing through any round opening spreads out a little, a wave effect called diffraction. A point of light turns into a small blurry disc with faint rings. If two stars are so close that their discs overlap too much, they blur into one.

The Rayleigh criterion gives the smallest angle at which two points can still be told apart: θ = 1.22λ/D. For green light of 550 nm and a 5 mm eye pupil, θ ≈ 1.3 × 10⁻⁴ rad, about half an arcminute.

The Hubble Space Telescope has a mirror 2.4 m across. The same light gives θ ≈ 2.8 × 10⁻⁷ rad, roughly 500 times finer than the eye.

This is why astronomers keep building bigger telescopes, and why radio telescopes far apart on the Earth are linked together to act like one giant dish.