Wilhelm Heinrich Walter Baade (March 24, 1893 – June 25, 1960) was a German
astronomer
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...
who worked in the United States from 1931 to 1959.
Biography
The son of a teacher, Baade finished school in 1912. He then studied maths, physics and astronomy at the universities of
Münster
Münster (; nds, Mönster) is an independent city (''Kreisfreie Stadt'') in North Rhine-Westphalia, Germany. It is in the northern part of the state and is considered to be the cultural centre of the Westphalia region. It is also a state di ...
and
Göttingen
Göttingen (, , ; nds, Chöttingen) is a university city in Lower Saxony, central Germany, the capital of the eponymous district. The River Leine runs through it. At the end of 2019, the population was 118,911.
General information
The ori ...
. After receiving his PhD in 1919, Baade worked at Hamburg Observatory at Bergedorf from 1919 to 1931. There in 1920 he discovered
944 Hidalgo
944 Hidalgo is a centaur and unusual object on an eccentric, cometary-like orbit between the asteroid belt and the outer Solar System, approximately in diameter. Discovered by German astronomer Walter Baade in 1920, it is the first member of t ...
, the first of a class of minor planets now called
Centaurs
A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse.
Centaurs are thought of in many Greek myths as being ...
which cross the orbits of giant planets.
He worked at
Mount Wilson Observatory
The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles.
The observat ...
from 1931 to 1958. There, during
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
, he took advantage of wartime blackout conditions (which reduced
light pollution
Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day ...
), to resolve stars in the center of the
Andromeda Galaxy
The Andromeda Galaxy (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy with the diameter of about approximately from Earth and the nearest large galaxy to the Milky Way. The gal ...
for the first time. These observations led him to define distinct "
populations
Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
" for stars (Population I and Population II). The same observations led him to discover that there are two types of
Cepheid variable
A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.
A strong direct relationship between a Cepheid vari ...
stars. Using this discovery he recalculated the size of the known universe, doubling the previous calculation made by Edwin Hubble in 1929. He announced this finding to considerable astonishment at the 1952 meeting of the
International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
in Rome.
Together with
Fritz Zwicky
Fritz Zwicky (; ; February 14, 1898 – February 8, 1974) was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical an ...
, he identified supernovae as a new category of astronomical objects. Zwicky and he also proposed the existence of
neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...
s, and suggested supernovae might create them.
Beginning in 1952, he and
Rudolph Minkowski
Rudolph Minkowski (born Rudolf Leo Bernhard Minkowski ; ; May 28, 1895 – January 4, 1976) was a German-American astronomer.
Biography
Minkowski was the son of Marie Johanna Siegel and physiologist Oskar Minkowski. His uncle was Hermann Min ...
identified the optical counterparts of various
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...
sources, including Cygnus A. He discovered 10 asteroids, including
944 Hidalgo
944 Hidalgo is a centaur and unusual object on an eccentric, cometary-like orbit between the asteroid belt and the outer Solar System, approximately in diameter. Discovered by German astronomer Walter Baade in 1920, it is the first member of t ...
, which has a long orbital period (it is actually the first centaur ever discovered, although they were not recognized as a distinct dynamical class until 1977); the
-class 1566 Icarus, the perihelion of which is closer than that of Mercury; and the Amor-type
1036 Ganymed
1036 Ganymed, provisional designation ', is a stony asteroid on a highly eccentric orbit, classified as a near-Earth object of the Amor group. It was discovered by German astronomer Walter Baade at the Bergedorf Observatory in Hamburg on 23 Oct ...
Gold Medal of the Royal Astronomical Society
The Gold Medal of the Royal Astronomical Society is the highest award given by the Royal Astronomical Society (RAS). The RAS Council have "complete freedom as to the grounds on which it is awarded" and it can be awarded for any reason. Past awar ...
(1954)
*
Bruce Medal
The Catherine Wolfe Bruce Gold Medal is awarded every year by the Astronomical Society of the Pacific for outstanding lifetime contributions to astronomy. It is named after Catherine Wolfe Bruce, an American patroness of astronomy, and was fi ...
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
Magellan
Ferdinand Magellan ( or ; pt, Fernão de Magalhães, ; es, link=no, Fernando de Magallanes, ; 4 February 1480 – 27 April 1521) was a Portuguese explorer. He is best known for having planned and led the 1519 Spanish expedition to the East ...
telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observ ...
s
*The asteroid 966 Muschi, after his wife's nickname
See also
* Baade's Window, an observational area he identified in the 1940s as being relatively free of dust that presents a view of the
Galactic Center
The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact ra ...
Crab Pulsar
The Crab Pulsar (PSR B0531+21) is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054, which was widely observed on Earth in the year 1054.Crab Nebula by him.