Joseph Lockyer (1836-1920, British) was the astronomer who first discovered the element
Helium when he was studying the Sun"s atmosphere.
Annie Jump Cannon (1863-1941, American) was a member of the famous group of Harvard
astronomers called "Pickering"s Women". She single-handedly classified 400,000 stars into the
scheme we use today (O B A F G K M), and discovered 300 variable stars.
Karl Schwarzschild (1873-1916, German) was the first to study the theory of black holes.
Albert Einstein (1879-1955, German) was probably the greatest mind of the twentieth century.
His Special Theory of Relativity, proposed in 1905, extended Newtonian Mechanics to very
large speeds close to the speed of light. It describes the changes in measurements of physical
phenomena when viewed by observers who are in motion relative to the phenomena. In 1915,
Einstein extended this further in the General Theory of Relativity, which includes the effects of
gravitation. According to this theory, mass and energy determine the geometry of space-time,
and curvatures of space-time manifest themselves in gravitational forces.
Edwin Hubble (1889-1953, American) made an incredible contribution to astronomy and
cosmology when he discovered that faraway galaxies are moving away from us. Known as
Hubble"s Law, the theory states that galaxies recede from each other at a rate proportional to
their distance from each other. This concept is a cornerstone of the Big Bang model of the
Gerard Kuiper (1905-1973, Dutch-born American) discovered a large number of comets at the
edge of the solar system beyond Pluto"s orbit, known as the Kuiper belt. He also discovered
several moons in the outer solar system and the atmosphere of Saturn"s moon Titan.
Subramanyan Chandrasekhar (1910-1995, Indian-born American) made important
contributions to the theory of stellar evolution. He found that the limit, now called the
Chandrasekhar limit, to the stability of white dwarf stars is 1.4 solar masses: any star larger than
this cannot be stable as a white dwarf.
James Van Allen (1914 - 2006, American) discovered the magnetosphere of the Earth. The
belts of radiation surrounding the planet are called the Van Allen belts, and moderate the
amount of solar radiation hitting Earth.
Robert Dicke (1916 - 1997, American) believed that it was possible to detect radiation left over
from the Big Bang. He invented the microwave radiometer to detect this radiation, which has a
wavelength of one centimeter.
Alan Sandage (1926 - 2010, American) calculated the ages of many globular clusters, and
discovered the first quasar.
Roger Penrose (1931-, British) expanded the physics of black holes by showing that
singularities in space were responsible for their existence.