"Another one airborne."
THE DAILY ASTRONOMER
Monday, July 25, 2016
Galileo's Ego
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CHRISTMAS IN JULY!
On
Monday, July 25, 2016 we're opening a secret space-time conduit from
this gloriously hot summer into the festive winter season. Today only,
you can see our annual holiday show "Season of Light." Narrated by
NPR's Noah Adams, this show examines the historical and astronomical
aspects of the holiday season. What is the origin of Santa Claus, the
solstice festivals, Hannukkah, New Year's Eve and the other traditions.
Showings at 11:00 a.m. and 1:00 p.m. today.
Admission $5.50 - adults; $5.00 - children, seniors
Note: After today, the next public showing of "Season of Light" is scheduled for November 26
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Well,
we won't empty Pandora's Jar before the school year ends on August 2.
Honestly, we didn't expect to do so. We're receiving more questions
that we're answering, presently. We'll step up our pace a bit but,
happily, we'll never catch up. Today, we address a question that is
more historical than astronomical.
"The Galilean Moons were named for Galileo, who discovered them. Did he name them after himself? If so, what an ego!" -Anonymous, Portland
Greetings!
Well, some scientific historians have claimed that Galileo did think well of himself. After all, he was Galileo
Galilei. However, he wasn't so self-serving as to have named
Jupiter's four largest moons after himself. That happened well
after their discovery. Now, we'll review some history. Galileo was
said to have discovered Jupiter's four largest satellites in 1609 or
early 1610, soon after he made modifications to the telescope.* These
moons are, in order going away from Jupiter, Io, Europa, Ganymede and
Callisto.
A copy of a page from Galileo's "Sidereus Nuncius,' ("The Starry Messenger") 1610. Here
we see Jupiter depicted as a large circle with smaller "stars" at
either side of that represent the "Galilean Moons," Io, Europa,
Ganymede and Callisto. Each image shows Jupiter on different nights.
We see how the configuration of these moons varies over time, thereby
indicating orbital motion around Jupiter. Image: History of Science Collections, University of Oklahoma Libraries
He
first recorded the discovery of these moons in his book "Sidereus
Nuncius," (The Starry Messenger.) He named these Jovan
satellites "Cosmica Sidera," after his patron Cosimo II de' Medici, the
Duke of Tuscany. Galileo had served as Medici's tutor when the latter
was a child and in adulthood Medici was one of Galileo's most loyal
patrons and supporters. Naming the moons for his patron was a grand
gesture of gratitude or, perhaps, a calculated means of assuring that
the patronage would continue. Some claim that the Duke, himself,
suggested the name and the politically astute Galileo readily agreed.
The
"Galilean Moons" (L-R) Io, Europa, Ganymede and Callisto. Although
Galileo is credited with their discovery, he did not assign them these
mythological names. Image: Pearson Education, Inc.
Interestingly
-well, it's interesting to us- the actual names of the individual
moons, -Io, Europa, Ganymede and Callisto- were coined by German
Astronomer Simon Marius (1573-1624). Marius claimed to have discovered
the same moons five weeks prior to Galileo's first observation of
them. However, as Marius did not publish his results, Galileo received
the credit for their discovery. At Johannes Kepler's suggestion.
Marius did name the moons after some of Zeus' lovers. Galileo refused
to confer these mythological names onto the moons, opting instead to
assign them the Roman numerals I, II, III, and IV, a convention that
some astronomical charts still use today.
*Galileo
Galilei did not invent the telescope. German-Dutch lens maker Hans
Lippershey (1570-1619) is credited with having invented the telescope,
but even this claim is uncertain. While in Venice, Galileo learned of
this new invention, then called the "Dutch Perspective Glass," capable
of enlarging distant objects to allow for closer scrutiny. He returned
to Padua and constructed his own device with certain modifications. He
devoted a year to perfecting the telescope and enhancing its
capabilities. He eventually built a telescope capable of magnifying an
image