astronomer who made observations that doubled the distance, scale, and
age of the universe.
He discovered that
stars are in two distinct populations according to their age, known
as Population I (the younger) and Population II (the older).
found that Cepheid variable stars of Population I are brighter than
had been supposed and that distances calculated from them were wrong.
Baade, born in Shröttinghausen,
studied at Münster and Göttingen.
He emigrated to
the USA 1931, working at Mount Wilson Observatory, Pasadena, California,
until 1948 and nearby Mount Palomar Observatory until 1958, when he
returned to Germany.
During World War
II, in 1943, Baade made use of the blackout darkness to study the Andromeda
galaxy and was able to observe, for the first time, some of the stars
in the inner regions of the galaxy.
He found that the
most luminous stars towards the centre are not blue-white but reddish,
and proposed that these have differing structures and origins.
Population I stars,
bluish, are young and formed from the dusty material of the spiral arms
- hydrogen, helium, and heavier elements; Population II stars, reddish,
are old, were created near the nucleus and contain fewer heavy elements.