This Day In History : September 23

1846 Germany

Neptune discovered

Neptune was discovered on September 23, 1846. The discovery was made by Johann Gottfried Galle, a German astronomer, based on calculations by Urbain Le Verrier, a French mathematician. This marked a significant milestone in astronomy, as Neptune became the first planet to be discovered through mathematical predictions rather than empirical observation alone.

Also on This Day in History September 23

Discover what happened on September 23 with HISTORY's summaries of major events, anniversaries,
famous births and notable deaths.

Births on This Day, September 23
  • 1819 Armand-Hippolyte-Louis Fizeau

    French physicist who was the first to measure the speed of light successfully without using astronomical calculations (1849)

  • 1838 Victoria Woodhull

    American civil rights activist (1872 presidential candidate, woman's suffrage movement)

  • 1863 Mary Church Terrell

    American educator and civil rights activist (co-founder and President National Association of Colored Women)

  • 1861 Robert Bosch

    German engineer, inventor (automotive ignition device), and industrialist

  • 1880 John Boyd Orr

    Scottish physician (Nobel Peace Prize 1949 - Father of the Food and Agriculture Organization)

Deaths on This Day, September 23
  • 1900 William Marsch Rice

    American businessman who founded Rice University in Houston, Texas

  • 1939 Sigmund Freud

    Austrian neurologist and father of psychology

  • 1882 Friedrich Wöhler

    German chemist who co-discovered vanadium

  • 1877 Urbain-Jean-Joseph Le Verrier

    French astronomer (made calculations that proved existence of Neptune)

  • 1929 Richard Adolf Zsigmondy

    Austrian-born chemist (1925 Nobel Prize for Chemistry for work colloids)


Roland Garros from France becomes the first to fly in an airplane across the Mediterranean

Roland Garros from France became the first pilot to fly across the Mediterranean Sea on September 23, 1913. He flew from Fréjus, France, to Bizerte, Tunisia, covering a distance of approximately 730 kilometers (454 miles) in a single-engine aircraft. This achievement marked a significant milestone in aviation history, demonstrating the feasibility of long-distance flights over large bodies of water.

The unification of Saudi Arabia is completed

The unification of Saudi Arabia was completed on September 23, 1932. This marked the consolidation of various regions and tribes under the leadership of Abdulaziz Ibn Saud, who became the first King of Saudi Arabia. The unification brought stability and cohesion to the Arabian Peninsula, establishing the modern state of Saudi Arabia as it is known today.

Time capsule, to be opened in 6939, buried at World's Fair in NYC

The time capsule, intended to be opened in the year 6939, was buried at the 1939-1940 New York World's Fair. This event marked a significant moment in history as it captured the spirit and achievements of the time for future generations to discover and learn about life in the late 1930s.

NASA announces that it has lost contact with the Mars Climate Orbiter

NASA announced that it had lost contact with the Mars Climate Orbiter on September 23, 1999. This loss occurred due to a navigation error caused by conflicting measurement units (imperial versus metric) used in ground-based software and the spacecraft's operations. The incident highlighted the importance of standardized units and rigorous testing in space missions.
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