| 1846 |
 |
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Calculations of Adams and Leverrier lead to discovery of Neptune. Adams and
Leverrier independently calculated the location of the unknown planet, Neptune, that was required to explain discrepancies in the orbit of Uranus. p. 288-289, F 9.23
|
| 1851 |
|
|
Jean Foucault uses pendulum to demonstrate
Earth rotates. Foucault showed that the pendulum swung in the same plane but the Earth rotated under it, causing an apparent change in the direction of the pendulum's swing. p. 144
|
| 1859 |
|
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James Clerk Maxwell discovers velocity distribution
function for a gas. Maxwell showed that the distribution of velocities of the atoms or molecules in a gas depends on temperature and the mass of the molecules.
|
| 1862 |
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William Huggins identifies chemical elements in stars.
Huggins studied the spectra of bright stars and found that the dark lines in their spectra matched the wavelengths of atoms measured in terrestrial laboratories. p. 363.
|
| 1871 |
|
|
Asaph Hall discovers
Phobos and Deimos. Remarkably, the prediction that Mars had two small satellites was made by Jonathan Swift 151 years before Hall's discovery. p. 262, F 8.24
|
| c1875 |
|
|
Lord Kelvin and Hermann von Helmholtz estimate the age of the Sun.
Kelvin and Helmholtz independently calculated the length of time it would have taken for the Sun to have shrunk to its present size. This time, called the Kelvin-Helmholtz time, is about 20 million years. p. 333
|
| 1877 |
|
|
Giovanni Schiaparelli
discovers "canals" of Mars. Schiaparelli reported
thin, dark lines crisscrossing the surface of Mars. The discovery raised the possibility of intelligent life on Mars. p. 262-263, F 8.25
|
| 1879 |
|
|
Joseph Stefan finds the rate at which a blackbody
emits energy. Stefan found that the energy emitted by a blackbody increases as the fourth power of temperature. p. 102.
|
| 1894 |
|
|
Wilhelm Wien finds how temperature affects the color
of
a blackbody. Wien found that a blackbody gets bluer as its temperature increases. p. 102.
|
| 1900 |
|
|
Max Planck presents formula of spectral distribution of
a blackbody. Planck found the way that the energy emitted by a blackbody depends on its wavelength and the temperature of the blakbody. p. 102.
|
| 1904 |
|
|
J. Hartmann finds interstellar
absorption lines. Hartmann found a very narrow line of calcium that didn't change in wavelength as the spectral lines from the two stars in a binary star system shifted back and forth.
|
| 1905 |
|
|
Albert Einstein explains the photoelectric efect.
Einstein explained that the emission of electrons only by light at short wavelengths occurs because light consistes of bundles of energy called photons. p. 95, F 3.2
|
| 1905 |
|
|
Einar Hertzsprung plots absolute magnitude versus spectral type.
Hertzsprung found that the stars are concentrated in a few regions of such a diagram, which became known as an Hertzsprung-Russell (or H-R) diagram. p. 372-373, F 12.17, F 12-18.
|
| 1905 |
|
|
Jacobus Kapteyn uses star counts to map Milky Way.
Using star counts, Kapteyn determined that the Sun lay 2000 pc from the center of a flattened galaxy. p. 442-443
|
| 1913 |
|
|
Henry Norris
Russell independently invents H-R diagram. The H-R
diagram became an important tool for understanding the evolution of stars. p. 372-373, F 12.17, F 12-18
|
| 1915 |
|
|
Alfred Wegener proposes continental
drift. Wegener noted the similarity of rocks on opposite sides of the Atlantic Ocean and proposed that the present continents had been part of a supercontinent that broke apart about 200 million years ago. p. 134, F 4.13
|
| 1916 |
|
|
Albert Einstein's general
theory of relativity. Einstein explained that matter curves space, causing bodies to move in ways we attribute to gravity. p. 518
|
| 1916 |
|
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Karl Schwarzschild calculates geometry of black hole.
Schwarzschild found that if a massive body is compressed to a very small size it curves space around it so severely that it forms a black hole. p. 424, F 14.12
|
| 1917 |
|
|
100" Mt. Wilson
telescope completed. The Mt. Wilson telescope was the largest optical telescope in the world for 31 years until the Palomar reflector was completed.
|
| 1917 |
|
|
V. M. Slipher obtains radial velocities for 25 galaxies. Slipher
found that 21 of the 25 galaxies had red shifted spectral lines, indicating that they are moving away from the us. p. 486, F 16.16
|
| 1918 |
|
|
Harlow Shapley find the size and shape of the
Milky Way. Shapley assumed that globular clusters are distributed uniformly about the center of the Milky Way. From this, he found that the Earth is located 15,000 pc from the center of the Milky Way. p. 442-443, F 25.6
|
| 1918 |
|
|
Annie J. Cannon and co-workers present thousands of stellar spectral classifications in the Henry Draper Catalogue.
Cannon and her co-workers devised a classification system for stellar spectra and used it to produce a catalog of spectra classifications for about 225,000 stars. p. 364-366, F 12.10
|
| 1920 |
|
|
M.N. Saha shows that the temperature of a star determines the appearance
of its spectrum. Saha showed that temperature differences rather are responsible for the existence of different spectral classes of stars. p. 364
|
| 1920 |
|
|
A. S. Eddington proposes that fusion powers the Sun.
Eddington suggested that the fusion of hydrogen, the most common element in the Sun, into helium provides the enormous energy output of the Sun. p. 333.
|
| 1923 |
|
|
Edwin Hubble shows spiral
nebulae are galaxies. Hubble identified individual Cepheid variable
stars in spiral nebulae and used them
to show that the spiral nebulae are huge collections of stars far from the Milky Way. p. 475-479, F 16.1, F 16.3, F 16.4, F 16.5, F 16.6, F 16.7.
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