| 1925 |
 |
|
|
Cecilia Payne shows stars of different classes have
essentially the same chemical composition.
Payne determined the chemical composition of a number of stars of different spectral classes and found that they were nearly the same. p. 364-365
|
| 1928 |
|
|
Arthur Holmes proposes mantle convection drives continental drift. Holmes
proposed
that convenction currents in the layer Beneath the
Earth's crust push the continents about. p. 133, F 4.10
|
| 1929 |
|
|
Edwin Hubble discovers
universe is expanding. Hubble found that the speed of recession of galaxies increases with distance. He explained that this is due to the expansion of the universe. p. 517-518, F 17.12
|
| 1930 |
|
|
S. Chandrasekhar shows white dwarf stars are made
of degenerate electrons. Chandrasekhar also showed that the more massive a white dwarf, the smaller it is and that there is a maximum mass, the Chandrasekhar limit, that a white dwarf can have. p. 416
|
| 1930 |
|
|
Clyde Tombaugh
discovers Pluto. Tombaugh discovered
Pluto by comparing photographic plates taken of the same region of the sky about a week apart. Pluto's image moved among the stars. p. 292-293, F 9.27, 9.28, 9.29
|
| 1930 |
|
|
Robert Trumpler discovers
diffuse interstellar dust. Trumpler found
that distant star clusters were bigger
than nearby star clusters. He reasoned that this was because interstellar dust made distant clusters look fainter and, hence, more distant. p. 452-454, F 15.13, F 15.14, F 15.15, F 15.16.
|
| 1931 |
|
|
Karl Jansky makes first radio astronomy observations.
Jansky found that the Milky Way galaxy is a source of radio emission. p. 463.
|
| 1937 |
|
|
Grote
Reber builts first radio telescope. Reber
built the first antenna specifically designed for radio astronomy. Using the radio telescope, Reber made the first map of cosmic radio emission. p. 164-165, F 15.16
|
| 1939 |
|
|
Robert Oppenheimer and George
Volkoff calculate properties of neutron stars. Oppenheimer and Volkoff
calculated that a neutron star would be only about 10 km
in radius. p. 418-424, F 14.5, F 14.6, F 14.7, F 14.8, F 14.9, F 14.10, F 14.11
|
| 1944 |
|
|
H.C. van de Hulst predicts 21 cm line of interstellar hydrogen.
van de Hulst calculated that interstellar hydrogen atoms emit a spectral line at a wavelength of 21 cm in the radio part of the spectrum. He suggested that it would be possible to detect the 21 cm line using radio telescopes. p. 456, F 15.19
|
| 1948 |
|
|
200" Palomar
telescope completed. The Palomar telescope was the world's largest high quality optical telescope for over 40 years. p. 163
|
| 1950 |
|
|
Jan Oort predicts existence of Oort Cloud of
comets. Oort analyzed the orbits of comets entering the inner solar system for the first time. He proposed that these new comets originate in a cloud of comets tens of thousands of astronomical units from the Sun. p. 222, F 7.4.
|
| 1951 |
|
|
Harold Ewen and Edward Purcell detect 21 cm
line. Ewen and Purcell used a radio telescope to detect emission from interstellar hydrogen atoms. p. 457-458.
|
| 1951 |
|
|
Gerard Kuiper proposes existence of Kuiper Belt of comets.
Kuiper proposed that the comets with periods of less than 200 years originate in a flatted belt of comets whose inner edge lies just beyond the orbit of Neptune. p. 307-308, F 10.11.
|
| 1958 |
|
|
James Van Allen discovers Van Allen radiation belts.
Explorer 1, the first satellite launched by the United States, carried a Geiger counter built by Van Allen. The Geiger counter showed that there are zones of trapped energetic ions and electrons beyond Earth's atmosphere. p. 143-144, F 4.20.
|
| 1960 |
|
|
Frank Drake uses radio telescope to search for interstellar signals.
Drake searched at a wavelength of 21 cm for artificial signals from creatures on planets orbiting two nearby stars. No signals were detected. p. 457-458.
|
| 1960 |
|
|
Robert Leighton discovers solar oscillations. Leighton found that the Sun vibrates at a variety of frequencies.
|
| c1960 |
|
|
Harry Hess suggests mid-ocean ridges due to
plate tectonics. Hess suggested that the mid-ocean ridges occur where the ocean floor splits apart due to plate tectonics and magma oozes out to form new ocean floor. p. 133-136, F 4.11
|
| 1961 |
|
|
Horace Babcock
proposes model for sunspot cycle. Babcock's model
involved the twisting of solar magnetic fields lines because the rate of solar rotation varies with solar latitude. p. 343-346, F 11.24, 11.25, 11.26
|
| 1963 |
|
|
Raymond Davis builds first solar neutrino
telescope. Davis used a large tank of cleaning fluid a mile deep in a gold mine to detect neutrinos produced in nuclear reactions in the Sun's core. p. 336-337, F 11.12
|
| 1963 |
|
|
Maarten Schmidt shows quasars have large
redshifts. Schmidt found that previously unidentified lines in the the spectrum of the quasar 3C 273 were actually redshifted lines of hydrogen. This showed that quasars are moving rapidly away from us and are extremely distant. p. 492, F 16.23
|
| 1964 |
|
|
Arno Penzias and Robert Wilson discoverd cosmic
background
radiation. Penzias and Wilson used a radio telescope to detect the highly redshifted radiation from the early stages in the expansion of the universe. p. 513-514, F 17.7, 17.8
|
| 1964 |
|
|
C.-C. Lin and Frank Shu explain spiral arms of
Milky Way. Lin and Shu explained that the spiral arms are the crests of density waves that rotate through the galaxy. p. 444-445, F 15.7.
|
| 1965 |
|
|
Mariner 4 flies past Mars.
Mariner 4 sent back pictures of Mars that showed a deal planet whose surface resembled that of the Moon. p. 254-255, F 8.16
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