On This Day

Galileo Galilei discovers the first three moons of Jupiter: Io, Europa and Ganymede

There are 97 known moons of the planet Jupiter. This number does not include a number of meter-sized moonlets thought to be shed from the inner moons, nor hundreds of possible kilometer-sized outer…

There are 97 known moons of the planet Jupiter. This number does not include a number of meter-sized moonlets thought to be shed from the inner moons, nor hundreds of possible kilometer-sized outer irregular moons that were only briefly captured by telescopes. All together, Jupiter's moons form a satellite system, colloquially referred to as the Jovian system. The most massive of the moons are the four Galilean moons: Io, Europa, Ganymede, and Callisto, all of which were independently discovered in 1610 by Galileo Galilei and Simon Marius and were the first objects found to orbit a body that was neither Earth nor the Sun.

Historical Significance

There are 97 known moons of the planet Jupiter.

Key People

Galileo Galilei

physicist and astronomer

Italian physicist and astronomer

Events Before

  1. William Shakespeare's Sonnets are first published in London, perhaps illicitly, by publisher Thomas Thorpe

    William Shakespeare's Sonnets are first published in London, perhaps illicitly, by publisher Thomas Thorpe

  2. Samuel de Champlain shoots and kills two Iroquois chiefs at Ticonderoga, New York, setting the stage for French-Iroquois

    Samuel de Champlain shoots and kills two Iroquois chiefs at Ticonderoga, New York, setting the stage for French-Iroquois conflicts for the next 150 years

  3. Galileo Galilei presents his telescope to the Venetian Senate in Venice

    Galileo Galilei presents his telescope to the Venetian Senate in Venice

  4. Galileo Galilei demonstrates his first telescope to Venetian lawmakers, including the Doge (ruler) of Venice, Leonardo D

    Galileo Galilei demonstrates his first telescope to Venetian lawmakers, including the Doge (ruler) of Venice, Leonardo Donato

  5. English explorer Henry Hudson is the first European to sail into Delaware Bay, naming it South Bay

    Henry Hudson (1565 – disappeared 23 June 1611) was an English sea explorer and navigator during the early 17th century, best known for his explorations of present-day Canada and parts of the...

Events After

  1. Establishment of the Pontifical and Royal University of Santo Tomas, the Catholic University of the Philippines, the old

    Establishment of the Pontifical and Royal University of Santo Tomas, the Catholic University of the Philippines, the oldest existing university in Asia and the largest Catholic university in the world

  2. Mughal Emperor Jahangir marries his 20th, last and most influential wife Mehr-un-Nisa, awarding her the title Nur Jahan

    Mughal Emperor Jahangir marries his 20th, last and most influential wife Mehr-un-Nisa, awarding her the title Nur Jahan 'Light of the World'

  3. George Abbot appointed Archbishop of Canterbury

    George Abbot (29 October 1562 – 4 August 1633) was an English bishop who was Archbishop of Canterbury from 1611 to 1633.

  4. Word "telescope" is 1st used by Prince Federico Cesi

    Word "telescope" is 1st used by Prince Federico Cesi

  5. Matthias von Habsburg chosen as King of Bohemia

    Matthias von Habsburg chosen as King of Bohemia

More from the 1610s

Frequently Asked Questions

What happened on January 7, 1610?
There are 97 known moons of the planet Jupiter. This number does not include a number of meter-sized moonlets thought to be shed from the inner moons, nor hundreds of possible kilometer-sized outer irregular moons that were only briefly captured by telescopes. All together, Jupiter's moons form a satellite system, colloquially referred to as the Jovian system.
Why is Galileo Galilei discovers the first three moons of Jupiter: Io, Europa and Ga... significant?
There are 97 known moons of the planet Jupiter.
Who was involved in Galileo Galilei discovers the first three moons of Jupiter: Io, Europa and Ga...?
Key figures include Galileo Galilei (physicist and astronomer).

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