The Hydrogen Question

The assumption that the planets and the Sun formed from the same basic material was verified as spectroscopic technique improved during the early 20th century, and more terrestrial elements were found in the solar spectrum. British astronomer Alfred Fowler (1868-1940) (see Bruce Medalists, page 249) wrote in 1918 that, as work proceeds, it becomes less and less probably sic that the Sun contains any elements which do not also enter into the composition of the Earth. It seems natural to infer...

Cosmology

While astronomers debated our place in the universe, physicists tried to define what place actually meant. Does the universe have a center Is there a place that is not moving relative to all other places, a fixed background The search for answers to these questions led to the development of cosmology, the scientific (as opposed to theological) study of the origin and the evolution of the universe. Albert Einstein's special theory of relativity explained that two observers moving at a constant...

The Size of Stars

Since ancient times, people have known that not all stars are alike. But it was not until the 20th century that they began to discover why. In 1905, Ejnar Hertzsprung showed that the hottest stars are also the brightest stars. Differences in the brightness of stars of the same color or temperature were a result of distance. Using the parallax of stars (see figure on page 24), Hertzsprung found that both the brightest and faintest red stars had small parallaxes, meaning that they were equally...

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Percival Lowell publishes Mars and Its Canals George Ellory Hale observes strong magnetic fields in sunspots Percival Lowell publishes Mars as the Abode of Life Largest meteor impact in recorded history hits Tunguska River in Siberia Percival Lowell created this globe of Mars in 1907 showing canals that he considered evidence of intelligent life on Mars. (Lowell Observatory Archives, Coleman-Kennedy Collection) Percival Lowell created this globe of Mars in 1907 showing canals that he considered...

Scientist of the Decade Edwin Powell Hubble 18891953

A man called the greatest astronomer since Galileo, Edwin Hubble proved the existence of other galaxies and that the universe is expanding. Hubble was born November 20, 1889, in Marshfield, Missouri. His father was an insurance agent and moved the family to Chicago when Edwin was nine. He graduated from the University of Chicago in 1910 at age 20 with a degree in math and astronomy. A gifted athlete as well as a top student, Hubble won a Rhodes scholarship and headed to Oxford in England....

Xray and Neutrino Astronomy

Access to space meant access to the parts of the electromagnetic spectrum that are blocked by Earth's atmosphere (see figure below). Thus, the first observations of the Sun's X-ray spectrum occurred from space in 1962. On June 18, 1962, the first known and brightest X-ray source in the sky other than the Sun, Scorpius X-1, was discovered by instruments aboard a rocket. The rocket was launched by a team led by Riccardo Giacconi (1931- ) at American Science and Engineering in Massachusetts. By...

Abundant Support for the Big Bang Theory

In 1961, the front page of the London papers declared that the steady-state theory was dead. The reporters had been invited by Martin Ryle to witness his presentation of data that he felt dealt a death blow to the theory. In a survey of radio galaxies versus distance, he had found the number of intense radio sources increased with distance, a result consistent with more energetic galaxies in the past than the present. Ryle, still apparently stinging from Hoyle proving him wrong about radio...