Phases of Venus in the Ptolemaic and Copernican systems
It is important to note that this was the first empirical evidence (coming almost a century after Copernicus) that allowed a definitive test of the two models.
The Phases of Venus
Venus was observed to go through a sequence of phases similar to the Moon.
Phases of Venus
In December 1610, Galileo Galilei used his telescope to show that Venus went through phases, just like the Moon. This observation was incompatible with the Ptolemaic system.
The gibbous and full phases of Venus are impossible in the Ptolemaic model but possible in Copernican model (and Tychonic model too!).
14 (a) The phases of Venus, rendered at different points in the planet's orbit. If Venus orbits the Sun and is closer to the Sun than is Earth, as Copernicus maintained, then Venus should display phases, much as our Moon does.
His discoveries of the four largest moons of Jupiter and the phases of Venus were persuasive evidence for the Copernican cosmology.
The Galileoscope project offers low cost 50 millimetre diameter telescopes that allow budding astronomers to view delights such as lunar craters and mountains, the Galilean satellites, the phases of Venus, Saturn's rings, ...
He made (1609) a small refracting telescope, turned it skyward, and discovered the phases of Venus, indicating that this planet revolves around the sun; he also discovered four moons revolving around Jupiter, as well as the rings of Saturn.
Galileo discovered four moons of Jupiter, observed the phases of Venus, studied sunspots, and discovered many other important phenomena.
An observer on Mars would be able to see the Earth go through phases similar to those that an Earth-bound observer sees the phases of Venus (as discovered by Galileo).
A complete cycle of phases is observable for the inferior planets, Mercury and Venus. Observations of the phases of Venus by Galileo were used to support the Copernican model of the Solar System.
performed fundamental observations, experiments, and mathematical analyses in astronomy and physics; discovered mountains and craters on the moon, the phases of Venus, and the four largest satellites of Jupiter: Io, Europa, Callisto, and Ganymede ...
The system nevertheless had a large influence on scientists such as Galileo and Kepler, who adopted, championed and, in Kepler's case, improved the model. Galileo's observation of the phases of Venus produced however the first observational evidence ...
Galileo discovered the rings of Saturn (1610), was the first person to see the four major moons of Jupiter (1610), observed the phases of Venus, studied sunspots, and discovered many other important phenomena.
Since it is closer to the Sun than the Earth, the illumination of Mercury's disk varies when viewed with a telescope from our perspective. Galileo's telescope was too small to see Mercury's phases but he did see the phases of Venus.
Venus comes closer to the Earth than any other planet, and appears to be the second brightest object in the night sky. Because of its closeness, astronomers on Earth can easily see the phases of Venus with binoculars.
of stars; he discovered the satellites of Jupiter and named them Sidera Medicea (Medicean Stars) in honour of his former pupil and future employer, Cosimo II, grand duke of Tuscany. He also observed Saturn, spots on the Sun, and the phases of Venus .
Galileo's early telescopes were no more powerful than today's binoculars, and they were of much lower quality. Yet, using low power instruments, Galileo discovered four moons of Jupiter, mountains on the Moon, and the phases of Venus.
He found that the Moon was not smooth, but mountainous and pitted - just like the Earth! He subsequently used his newly invented telescope to discover four of the moons circling Jupiter, to study Saturn, to observe the phases of Venus, ...
 See also: Venus, Earth, Phase, Phases, Sun
  
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