Year of Discovery: 1610
Galileo discovered that other planets have moons and thus ex tended human under standing beyond our own planet. His careful work with the telescopes he built launched modern astronomy. His discoveries were the first astronomical discoveries using the telescope.
Galileo proved that Earth is not unique among planets of the uni verse. He turned
specks of light in the night sky into fascinating spherical objects—into places—rather than
pin pricks of light. In so doing, he proved that Polish astronomer Nicholaus Copernicus had
been right when he claimed that the sun was the center of the solar system.
With his simple telescope Galileo single-handedly brought the solar system, galaxy,
and greater uni verse within our grasp. His telescope provided vistas and understanding that
did not exist be fore and could not exist with out the telescope.
How Was It Discovered?
This was a discovery made possible by an invention—the telescope. Galileo saw his first
telescope in late 1608 and instantly recognized that a more powerful telescope could be the answer to the prayers of every astronomer. By late 1609 Galileo had produced a 40-power,
two-lens telescope. That 1609 telescope was the first practical telescope for scientific use.
A pa per by Johannes Kepler describing the or bits of the planets convinced Galileo to
believe the theory of Polish astronomer Nicholaus Copernicus, who first claimed that the
sun was the center of the uni verse, not the earth. Believing Copernicus was a dangerous
thing to do. Friar Giordano Bruno had been burned at the stake for believing Copernicus.
Galileo decided to use his new telescope to prove that Copernicus was right by more accurately charting the motion of the planets.
Galileo first turned his telescope on the moon. There he clearly saw mountains and valleys. He saw deep craters with tall, jagged rims slicing like serrated knives into the lunar
sky. The moon that Galileo saw was radically different from the perfectly smooth sphere
that Aristotle and Ptolemy said it was (the two Greek astronomers whose teachings still
formed the basis of all science in 1610). Both the all-powerful Catholic Church and every
university and scientist in Eu rope believed Aristotle and Ptolemy.
In one night’s viewing of the moon’s surface through his telescope, Galileo proved Aristotle wrong—again. The last time Galileo’s observations had contradicted Aristotle’s
teachings, Galileo had been fired from his teaching position for being right when he proved
that all objects fall at the same rate regardless of their weight.
Galileo next aimed his telescope at Jupiter, the biggest planet, planning to care fully
chart its motion over several months. Through his telescope (the name is a com bi nation of
the Greek words for “distant” and “looking”) Galileo saw a magnified view of the heavens
no human eye had ever seen. He saw Jupiter clearly, and, to his amazement, he found moons
cir cling the giant planet. Aristotle had said (and all scientists believed) that Earth was the
only planet in the uni verse that had a moon. Within days, Galileo discovered four of Jupiter’s moons. These were the first discovered moons other than our own.
Aristotle was wrong again.
Still, old beliefs do not die easily. In 1616 the Council of Cardinals for bade Galileo
ever again to teach or pro mote Copernicus’s theories. Many senior church officials re fused
to look through a telescope, claiming it was a magician’s trick and that the moons were in
the telescope.
When Galileo ignored their warning, he was summoned to Rome by the Church’s
all-powerful Inquisition. A grueling trial fol lowed. Galileo was condemned by the Church
and forced to publicly recant his views and findings. He was placed under house arrest for
the rest of his life, dying in 1640 with out hearing even one voice other than his own pro -
claim that his discoveries were true. The Church did not rescind the condemnation of Galileo and his discoveries until October 1992, 376 years after they incorrectly condemned him.
Galileo discovered that other planets have moons and thus ex tended human under standing beyond our own planet. His careful work with the telescopes he built launched modern astronomy. His discoveries were the first astronomical discoveries using the telescope.
Galileo proved that Earth is not unique among planets of the uni verse. He turned
specks of light in the night sky into fascinating spherical objects—into places—rather than
pin pricks of light. In so doing, he proved that Polish astronomer Nicholaus Copernicus had
been right when he claimed that the sun was the center of the solar system.
With his simple telescope Galileo single-handedly brought the solar system, galaxy,
and greater uni verse within our grasp. His telescope provided vistas and understanding that
did not exist be fore and could not exist with out the telescope.
How Was It Discovered?
This was a discovery made possible by an invention—the telescope. Galileo saw his first
telescope in late 1608 and instantly recognized that a more powerful telescope could be the answer to the prayers of every astronomer. By late 1609 Galileo had produced a 40-power,
two-lens telescope. That 1609 telescope was the first practical telescope for scientific use.
A pa per by Johannes Kepler describing the or bits of the planets convinced Galileo to
believe the theory of Polish astronomer Nicholaus Copernicus, who first claimed that the
sun was the center of the uni verse, not the earth. Believing Copernicus was a dangerous
thing to do. Friar Giordano Bruno had been burned at the stake for believing Copernicus.
Galileo decided to use his new telescope to prove that Copernicus was right by more accurately charting the motion of the planets.
Galileo first turned his telescope on the moon. There he clearly saw mountains and valleys. He saw deep craters with tall, jagged rims slicing like serrated knives into the lunar
sky. The moon that Galileo saw was radically different from the perfectly smooth sphere
that Aristotle and Ptolemy said it was (the two Greek astronomers whose teachings still
formed the basis of all science in 1610). Both the all-powerful Catholic Church and every
university and scientist in Eu rope believed Aristotle and Ptolemy.
In one night’s viewing of the moon’s surface through his telescope, Galileo proved Aristotle wrong—again. The last time Galileo’s observations had contradicted Aristotle’s
teachings, Galileo had been fired from his teaching position for being right when he proved
that all objects fall at the same rate regardless of their weight.
Galileo next aimed his telescope at Jupiter, the biggest planet, planning to care fully
chart its motion over several months. Through his telescope (the name is a com bi nation of
the Greek words for “distant” and “looking”) Galileo saw a magnified view of the heavens
no human eye had ever seen. He saw Jupiter clearly, and, to his amazement, he found moons
cir cling the giant planet. Aristotle had said (and all scientists believed) that Earth was the
only planet in the uni verse that had a moon. Within days, Galileo discovered four of Jupiter’s moons. These were the first discovered moons other than our own.
Aristotle was wrong again.
Still, old beliefs do not die easily. In 1616 the Council of Cardinals for bade Galileo
ever again to teach or pro mote Copernicus’s theories. Many senior church officials re fused
to look through a telescope, claiming it was a magician’s trick and that the moons were in
the telescope.
When Galileo ignored their warning, he was summoned to Rome by the Church’s
all-powerful Inquisition. A grueling trial fol lowed. Galileo was condemned by the Church
and forced to publicly recant his views and findings. He was placed under house arrest for
the rest of his life, dying in 1640 with out hearing even one voice other than his own pro -
claim that his discoveries were true. The Church did not rescind the condemnation of Galileo and his discoveries until October 1992, 376 years after they incorrectly condemned him.