A Lighthouse Seen from the Side: How Two Gamma-Ray Bursts Revealed the Shape of an Invisible Jet
Two snapshots of the same lighthouse. One is taken from a boat sailing straight into the beam, the other from the shore, where the beam only grazes the edge of the sky. From these two frames, you can reconstruct how the lighthouse light is distributed across angles without ever getting close to it. That is roughly what astronomers did with two gamma-ray bursts they consider twins.