This Day In History : March 21

1684 Italy

Giovanni Domenico Cassini Discovers Two Moons of Saturn: Tethys and Dione

On March 21, 1684, Giovanni Domenico Cassini identifies two previously unknown moons of Saturn, Tethys and Dione. This discovery adds to the knowledge of Saturn's satellite system. Cassini's observations enhance the understanding of planetary moons and their dynamics.

Also on This Day in History March 21

Discover what happened on March 21 with HISTORY's summaries of major events, anniversaries,
famous births and notable deaths.

Births on This Day, March 21
  • 1713 Francis Lewis

    Welsh-American merchant and US Founding Father, signer of the Declaration of Independence

  • 1866 Antonia Maury

    American astronomer who created own stellar classification

  • 1921 Joe Sutter

    American engineer and head of the Boeing 747 program

  • 1932 Walter Gilbert

    American molecular biologist

  • 1887 David Keilin

    Russian-British biochemist who discovered cytochromes

Deaths on This Day, March 21
  • 1915 Frederick Winslow Taylor

    American mechanical engineer and Father of scientific management

  • 1980 Peter Stoner

    American mathematician and astronomer

  • 2016 Robert McNeill Alexander

    British zoologist who estimated the speed of dinosaurs

  • 1991 Leo Fender

    American inventor, and electric guitar designer and manufacturer of electronic musical instruments

  • 1988 Patrick Steptoe

    British scientist and medical researcher who perfected in-vitro fertilization of the human egg

2006

Jack Dorsey Sends the World's First Tweet

On March 21, 2006, Jack Dorsey sent the first-ever Twitter message, marking the birth of the popular social media platform. This milestone initiated a new era of communication, enabling instant sharing of thoughts and updates worldwide.
1935

Persia Officially Renamed Iran

On March 21, 1935, Persia officially adopts the name "Iran," marking a significant shift in national identity. The change, announced by Reza Shah Pahlavi, reflects the country's desire to emphasize its Aryan heritage and modernize its image on the global stage.
1952

World's First Rock and Roll Concert Held in Cleveland

On March 21, 1952, Cleveland, Ohio hosts the world's first rock and roll concert, featuring pioneering artists who help define the genre. This historic event marks a pivotal moment in music history, showcasing the energy and appeal of rock and roll. The concert sets the stage for the genre's explosive growth in popularity.
1990

Namibia Gains Independence from South Africa

On March 21, 1990, Namibia achieves independence from South Africa, marking the end of a long struggle for self-determination. Sam Nujoma is inaugurated as the country's first president, ushering in a new era for the newly sovereign nation. This pivotal moment signifies the culmination of Namibia's fight for freedom.
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