Ying Zhang

For 39 years, astronomers have been recording how the star BE Lyn brightens and dims. Its light pulsates with a rhythm of several hours, like a lighthouse that never stops blinking. But there is a glitch in this rhythm: sometimes the flashes came a little early, sometimes a little late. The star was moving closer to Earth and then farther away, as if something were dragging it in a circle.

Two watermelons of equal weight sit on a counter. One is ripe, juicy, with a thick rind. The other looks as if carved from oak: inside it is completely different, and squeezing it is nearly impossible. They look like twins, but tap them, and the difference is obvious.