Baade, Walter 1893-1960. German-born US
astronomer, who made observations that
doubled the distance, scale and the age of
the universe. Baade worked at Mount Wilson
Observatory, USA, and discovered that stars
are in two distinct populations according to
their age, known as Population I (the
younger) and Population II (the older).
Later, he found that Cepheid variable stars
of Population I are brighter than had been
supposed, and that distances calculated from
them were wrong. Baade's figures showed that
the universe was twice as large as previously
thought, and twice as old.