View our new "On this day" sections for April


April 1 

  • 1933 Birth of Claude Cohen-Tannoudji, winner of the 1997 along with Steven Chu and William Daniel Phillips for research on laser cooling and trapping of atoms

April 2 

  • 1618 Birth of Francesco Maria Grimaldi, who coined the word "diffraction" and who, along with Giovanni Riccioli, showed that the distance travelled by a body in freefall is proportional to the square of the time it falls

April 3 

  • 1885 Gottlieb Daimler receives a patent in Germany for his petrol engine design

April 4 

  • 1949 Birth of Shing-Tung Yau, known for Calabi-Yau manifolds used in string theory, developed jointly with Eugenio Calabi

April 5 

  • 1622 Birth of Vincenzo Viviani, a disciple of Galileo's who took an early accurate measurement of the speed of sound by timing the delay between seeing a cannon's muzzle flash and hearing the sound of the shot
  • 1929 Birth of Ivar Giaever, the solid-state physicist who shared half of the 1973 Nobel Prize with Leo Esaki for their discovery of quantum tunneling in superconductors. The other half was awarded to Brian Josephson

April 6 

  • 1973 The Pioneer 11 spacecraft is launched to study Jupiter and Saturn
  • 1851 Birth of Guillaume Bigourdan, the astronomer who verified the positions of more than 6000 nebulae and discovered 500 new objects in the process
  • 1949 Birth of Horst Ludwig Störmer, who shared the 1998 Nobel Prize with Daniel Tsui and Robert Laughlin for their discovery of the fractional quantum Hall effect - a "new form of quantum fluid" in which excitations have charges that are fractional rather than whole numbers

April 7 

  • 1927 The first long-distance television broadcast takes place, transmitting the image of US Commerce Secretary Herbert Hoover from Washington, DC to New York City

April 8 

  • 2008 The first building to integrate wind turbines into its design, the Bahrain World Trade Center, is completed
  • 1732 Birth of David Rittenhouse, who used his observations of the transit of Venus to calculate the distance from the Earth to the Sun at 93 m miles (150 m km)

April 9 

  • 1860 The first audible recording of a human voice is made
  • 1959 NASA announces the selection of its first seven astronauts

April 10 

April 11 

  • 1905 Albert Einstein's special theory of relativity is published
  • 1970 Apollo 13 is launched
  • 1798 Birth of Macedonio Melloni, who discovered that radiant heat has properties similar to those of light
  • 1862 Birth of William Wallace Campbell, an astronomer specialising in spectroscopy who catalogued the radial velocities of stars and who led an expedition to photograph a solar eclipse in Australia in 1922, which was used to confirm predictions made by Einstein's general theory of relativity

April 12 

  • 1633 The trial of Galileo Galilei by the Inquisition begins
    1981 The first orbital test of a space shuttle, Colombia, takes place
    1851 Birth of Edward Walter Maunder, the astronomer known for his studies of sunspots and the Sun's magnetic cycle. The prolonged period in which there was little sunspot activity from 1645-1715 is known as the Maunder Minimum for him

April 13 

  • 1892 Birth of Robert Alexander Watson-Watt, the inventor of radar
    1909 Birth of Stanislaw Ulam, who developed the Teller-Ulam design of thermonuclear weapons jointly with Edward Teller and who first proposed the idea of nuclear pulse propulsion, in which a spacecraft could generate thrust via repeated nuclear explosions

April 14 

  • 1629 Birth of Christiaan Huygens, who showed that light is made up of waves, derived the formula for the centripetal force of an object in circular motion, and discovered a moon of Saturn, Titan, as well as explaining its rings

April 15 

  • 1707 Birth of Leonard Euler, known for his many contributions to maths, including application of mathematical tools to problems in physics
    1874 Birth of Johannes Stark, winner of the 1919 Nobel Prize for his discoveries of the Doppler Effect in beams of positive ions and of the splitting of spectral lines in an electric field - the latter is now known as the Stark effect

April 16 

  • 1495 Birth of Petrus Apianus, who discovered that a comet's tail always points away from the Sun

April 17 

  • 1970 Apollo 13 returns safely to Earth after its aborted trip to the moon
  • 1863 Birth of Augustus Edward Hough Love, known for his mathematical theory of elasticity and for his work on wave propagation

April 18 

  • 1911 Birth of Maurice Goldhaber, who discovered jointly with Lee Grodzins and Andrew Sunyar that neutrinos have a negative helicity.

April 19 

  • 1975 India launches its first satellite, Aryabhata
    1883 Birth of Richard von Mises, known for his contributions to mechanics and aerodynamics

April 20 

  • 1535 A parhelion - the appearance of a luminous ring around the Sun - is observed over Stockholm
  • 1902 Pierre and Marie Curie refine radium chloride
  • 1918 Birth of Kai Siegbahn, winner of the 1981 Nobel Prize along with Nicolaas Bloembergen and Arthur Schawlow for their work in laser spectroscopy
  • 1927 Birth of Karl Alexander Müller, who was awarded the 1987 Nobel Prize jointly with Johannes Georg Bednorz for their studies of superconductivity in ceramics

April 21 

  • 1882 Birth of Percy Williams Bridgman, who won the 1946 Nobel Prize for his studies of the properties of matter at high pressure, who came up with a set of equations of thermodynamics now named for him

April 22 

  • 1891 Birth of Harold Jeffreys, the mathematician, geophysicist and astronomer noted for first suggesting that the Earth's core is liquid and for his contributions to the Bayesian theory of probability
  • 1904 Birth of Robert Oppenheimer, considered to be the father of the atomic bomb and notable for his contributions to quantum physics including the first prediction of quantum tunneling

April 23 

  • 2009 A flash of gamma rays is observed for 10 seconds, at the time becoming the oldest known object in the universe
    1792 Birth of John Thomas Romney Robinson, who spent 34 years compiling a catalogue of 5345 stars
    1858 Birth of Max Planck, known for his eponymous blackbody radiation law and for founding quantum mechanics, for which he received the Nobel Prize in 1918

April 24 

  • 1990 The Hubble Space Telescope is launched

April 25 

  • 1983 The Pioneer 10 space probe travels beyond the orbit of Pluto
    1900 Birth of Wolfgang Pauli, known for his exclusion principle in quantum mechanics - that no two identical fermions can occupy the same state at the same time - for which he was awarded the Nobel Prize in 1945

April 26 

  • 1986 An accident occurs at the Chernobyl nuclear power plant in the USSR, present-day Ukraine, becoming the worst nuclear accident in history
    1994 The first experimental evidence of the existence of the top quark is announced
    1879 Birth of Owen Willans Richardson, who was awarded the 1928 Nobel Prize for his work on thermionic emission
    1933 Birth of Arno Allan Penzias, co-discoverer of the cosmic microwave background radiation along with Robert Woodrow Wilson - the pair shared half of the 1978 Nobel Prize with the other half being awarded to Pyotr Leonidovich for unrelated work

April 27 

  • 1981 The Palo Alto Research Center introduces the computer mouse
  • 2002 The last telemetry from Pioneer 10 is received

April 28 

  • 2001 Dennis Tito becomes the world's first space tourist
    1900 Birth of Jan Oort, the radio astronomer who confirmed that the Milky Way rotates, discovered the galactic halo, and who lends his name to the Oort Cloud - a hypothetical cloud of comets in the outer solar system

April 29 

  • 1953 The first 3D TV broadcast takes place

April 30 

  • 1006 The brightest supernova in recorded history appears in the constellation Lupus
  • 1777 Birth of Carl Friedrich Gauss, who made many contributions to maths and physics and particularly for his eponymous law in electromagnetism relating the electric flux through a closed surface to the enclosed charge