LIGHT & OPTICS · LAB 23

Gravitational lensing

Move a distant source behind a massive foreground object and watch gravity transform it into multiple images, arcs or an Einstein ring.

LENSING REGIMESTRONG LENSING

Drag the cyan source marker or amber lens to change their alignment

True sourceLens massApparent images

EINSTEIN RADIUS—

angular radius

IMAGES—

—

MAGNIFICATION—

—

DEFLECTION—

at Einstein radius

TIME DELAY—

educational estimate

WHAT TO NOTICE

Mass reshapes the sky

A foreground mass curves spacetime and bends light. Near-perfect alignment forms a ring; offset sources form arcs or separate images. Astronomers use these distortions to map dark matter and reveal otherwise invisible objects.

α = 4GM / c²bβ = θ − θE²/θ

Educational thin-lens approximation; distances and cosmology are simplified.