Pulsar
PSR B1919+21 — the first pulsar ever detected (Jocelyn Bell Burnell, 1967) — beating at its real 1.3373-second rotation period. Each line is one turn of the neutron star, written as the radio beam sweeps past and stacked into the waterfall made famous by Unknown Pleasures; sub-pulses drift steadily across the window pulse after pulse, the drifting-subpulse phenomenon this pulsar actually exhibits.