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Space5–7 minA solar eclipse and a lunar eclipse both involve the Sun, Earth, and Moon, but the shadow falls in a different place. In one, the Moon’s shadow reaches Earth; in the other, the Moon moves into Earth’s shadow. The Moon’s tilted orbit helps explain why these alignments do not happen every month.

Space5–7 minA star shines in every direction, while a planet catches only a tiny share of its light. A hypothetical swarm of orbiting collectors could intercept more, but collecting energy also means eventually disposing of heat. A Dyson swarm connects an enormous science-fiction idea to the ordinary questions of area, orbit and energy use.

Space8–10 minA star photographed on a glass plate a century ago can become a new measurement when compared with later observations. Harvard's DASCH project digitizes an astronomical plate archive, alongside dates and logbooks. Explore how calibration makes those old images useful for investigating changes across decades.

Space3–7 minImagine sunlight switching off while leaving the rest of the gravitational setup unchanged. The change would first have to reach Earth, and the planet would then cool by losing stored energy, making darkness and freezing two different events.

Space5–7 minA returning spacecraft has to manage an enormous transfer of energy as it slows in the atmosphere. Some heat shields protect the structure by changing and losing their own outer material, so damage to that layer can be part of the design.

Space3–7 minAn astronaut can float beside the ceiling while gravity still pulls the spacecraft toward Earth. When the cabin and everything inside are falling together, a floor label and the direction of gravity no longer feel like the same thing.

Space3–7 minThe 1974 Arecibo message encoded a picture as a stream of zeros and ones. Recovering its intended grid is only the first puzzle: recognizing its symbols requires assumptions about numbers, pictures, and the beings who sent it.

Space3–5 minSunlight illuminates half the Moon, while its changing position around Earth changes how much of that lit half we can see. A phase is different from an eclipse, where one body blocks light from reaching another.

Space3–7 minA small patch of “scruff” on a radio telescope chart kept returning from the same part of the sky. Jocelyn Bell Burnell’s account of the 1967 pulsar discovery follows the patient work of deciding whether that odd signal was interference or something new.

Space3–7 minNobody could ever count the atoms in the universe one by one, yet physicists often quote an estimate of roughly 10⁸⁰ atoms' worth of ordinary matter in the observable cosmos. Rather than counting individual particles, cosmologists work top-down: they measure the size and expansion of the observable universe, calculate the fraction made of ordinary matter rather than dark matter, and divide by the mass of a proton.

Space3–5 minA picture of an expanding universe can make it look as though every ruler must stretch too. The changing separation of distant cosmic locations and the forces that set a bound object’s size are different parts of the problem.

Space5–7 minA falling clock and someone watching it from far away would not tell the same black-hole story. In an ideal nonrotating model, elapsed time on the falling clock differs from what distant observers can reconstruct from increasingly delayed, dimmed signals.