born in Java, in modern Indonesia. In the early 1920s he began a search for stars with large proper motion in the hope of detecting nearby white dwarfs, only three of which were known in 1920. The search eventually yielded the proper motions of 120 000 stars, and added considerably to the number of known white dwarfs, which by 1960 had risen to 400, most of them found by Luyten. In 1947 he discovered a star in Cetus (UV Ceti) with high proper motion; this became the first flare star to be identified when photographs taken for measuring its parallax showed it to brighten and fade suddenly.