section_path: History/Ground-based telescope research
section_name: Ground-based telescope research
paragraph_text: Ground-based telescope research
  
  In 1610, Italian polymath Galileo Galilei discovered the four largest moons of Jupiter (now known as the Galilean moons) using a telescope. This is thought to be the first telescopic observation of moons other than Earth's. Just one day after Galileo, Simon Marius independently discovered moons around Jupiter, though he did not publish his discovery in a book until 1614. It was Marius's names for the major moons, however, that stuck: Io, Europa, Ganymede, and Callisto. The discovery was a major point in favour of Copernicus' heliocentric theory of the motions of the planets; Galileo's outspoken support of the Copernican theory led to him being tried and condemned by the Inquisition.
  
  In the autumn of 1639, the Neapolitan optician Francesco Fontana tested a 22-palm telescope of his own making and discovered the characteristic bands of the planet's atmosphere.
  
  During the 1660s, Giovanni Cassini used a new telescope to discover spots in Jupiter's atmosphere, observe that the planet appeared oblate, and estimate its rotation period. In 1692, Cassini noticed that the atmosphere undergoes a differential rotation.
  
  The Great Red Spot may have been observed as early as 1664 by Robert Hooke and in 1665 by Cassini, although this is disputed. The pharmacist Heinrich Schwabe produced the earliest known drawing to show details of the Great Red Spot in 1831. The Red Spot was reportedly lost from sight on several occasions between 1665 and 1708 before becoming quite conspicuous in 1878. It was recorded as fading again in 1883 and at the start of the 20th century.
  
  Both Giovanni Borelli and Cassini made careful tables of the motions of Jupiter's moons, which allowed predictions of when the moons would pass before or behind the planet. By the 1670s, Cassini observed that when Jupiter was on the opposite side of the Sun from Earth, these events would occur about 17 minutes later than expected. Ole Rømer deduced that light does not travel instantaneously (a conclusion that Cassini had earlier rejected), and this timing discrepancy was used to estimate the speed of light.
  
  In 1892, E. E. Barnard observed a fifth satellite of Jupiter with the 36-inch (910 mm) refractor at Lick Observatory in California. This moon was later named Amalthea. It was the last planetary moon to be discovered directly by a visual observer through a telescope. An additional eight satellites were discovered before the flyby of the Voyager 1 probe in 1979.
  
  In 1932, Rupert Wildt identified absorption bands of ammonia and methane in the spectra of Jupiter. Three long-lived anticyclonic features called "white ovals" were observed in 1938. For several decades, they remained as separate features in the atmosphere, sometimes approaching each other but never merging. Finally, two of the ovals merged in 1998, then absorbed the third in 2000, becoming Oval BA.