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The first observations of the full planetary phases of Venus were by Galileo at the end of 1610 (though not published until 1613 in the Letters on Sunspots).Using a telescope, Galileo was able to observe Venus going through a full set of phases, something prohibited by the Ptolemaic system that assumed Venus to be a perfect celestial body.
In particular, Galileo's observations of the phases of Venus, which showed it to circle the Sun, and the observation of moons orbiting Jupiter, contradicted the geocentric model of Ptolemy, which was backed and accepted by the Roman Catholic Church, [7] [8] and supported the Copernican model advanced by Galileo. [9]
Galileo's observations of the satellites of Jupiter caused controversy in astronomy: a planet with smaller planets orbiting it did not conform to the principles of Aristotelian cosmology, which held that all heavenly bodies should circle the Earth, [56] [57] and many astronomers and philosophers initially refused to believe that Galileo could ...
Because its orbit takes it between the Earth and the Sun, Venus as seen from Earth exhibits visible phases in much the same manner as the Earth's Moon. Galileo Galilei observed the phases of Venus in December 1610, an observation which supported Copernicus's then-contentious heliocentric description of the Solar System. [13]
In 1610, Galileo observed that Venus had a full set of phases, similar to the phases of the moon we can observe from Earth. This was explainable by the Copernican or Tychonic systems which said that all phases of Venus would be visible due to the nature of its orbit around the Sun, unlike the Ptolemaic system which stated only some of Venus's ...
However Cassini's observation did bear out Galileo's argument that sunspots indicated that the Sun was rotating, [62] and Cassini did discover the rotation of Mars and Jupiter, [63] which supported Galileo's contention that both the Earth and the Sun rotated.
The Venusian diameter of about 7,500 miles (12,000 km) is just a tad smaller than Earth's 7,900 miles (12,750 km). "Venus and Earth are often called sister planets because of their similarities in ...
Another set of observations was conducted using Galileo's energetic-particles detector (EPD) when Galileo moved through the bow shock caused by Venus's interaction with the solar wind. Earth's magnetic field causes the bow shock to occur at around 65,000 kilometers (40,000 mi) from its center, but Venus's weak magnetic field causes it to occur ...