The phases of Venus are the variations of lighting seen on the planet's surface, similar to lunar phases. The first recorded observations of them are thought to have been telescopic observations by Galileo Galilei in 1610. Although the extreme crescent phase of Venus has since been observed with the naked eye, there are no indisputable historical pre-telescopic records of it being described or known. [1]
The orbit of Venus is 224.7 Earth days (7.4 avg. Earth months [30.4 days]). The phases of Venus result from the planet's orbit around the Sun inside the Earth's orbit giving the telescopic observer a sequence of progressive lighting similar in appearance to the Moon's phases. It presents a full image when it is on the opposite side of the Sun. It is a gibbous phase when it approaches or leaves the opposite side of the Sun. It shows a quarter phase when it is at its maximum elongation from the Sun. Venus presents a thin crescent in telescopic views as it comes around to the near side between the Earth and the Sun and presents its new phase when it is between the Earth and the Sun. Since the planet has an atmosphere it can be seen at new in a telescope by the halo of light refracted around the planet. The full cycle from new to full to new again takes 584 days (the time it takes Venus to overtake the Earth in its orbit). Venus (like the Moon) has 4 primary phases of 146 days each.
The planet also changes in apparent size from 9.9 arc seconds at full (superior conjunction) up to a maximum of 68 arc seconds at new (inferior conjunction). [1] Venus reaches its greatest magnitude of about −4.5 when it is an intermediate crescent shape at the point in its orbit, when it is 68 million km away from the Earth, at which point the illuminated part of its disk reaches its greatest angular area as seen from the Earth (a combination of its closeness and the fact that it is 28% illuminated). [2]
Contrary to other planets its apparent magnitude around inferior conjunction does not decrease consistently but rather spikes before dimming further. This is caused by sulfuric acid droplets in Venus' atmosphere reflecting more light at a certain angle and thus phase, an effect similar to a glory on Earth. [3]
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 the Ptolemaic system, the Sun and Venus circle the earth, with Venus orbiting around a point on the Earth-Sun axis, so that Venus is never on the far side of the sun. One could never expect an alignment Sun-Earth-Venus or Venus-Sun-Earth to occur, so that a full Venus could never be observed. Galileo's observations of the phases of Venus [4] essentially ruled out the Ptolemaic system, and was compatible only with the Copernican system and the Tychonic system and other models such as the Capellan and Riccioli's extended Capellan model.
There is some controversy about Galileo's claim to first observing the phases of Venus: In December of 1610, Galileo received a letter from fellow scientist Benedetto Castelli, asking if the phases of Venus were observable through Galileo's new telescope. [5] Days later, Galileo wrote in a letter to Johannes Kepler saying that he had observed Venus going through phases, but took complete credit for himself. It is unclear, lacking copies of any earlier correspondence, whether Castelli was telling Galileo of it for the first time, or responding to Galileo having previously informed him of it. [6]
Curiously, Galileo's letter to Kepler was encrypted so that Kepler could not scoop Galileo before he had made more exhaustive observations: Galileo took a sentence stating that Venus went through phases:
And scrambled the letters into a strange anagram:
Cynthia was a popular epithet for the Moon, the mother of love of course being Venus. He sent the anagram to Kepler, then a few months later sent the decoded version. This way he had proof of having made the observation, without Kepler being able to publish it earlier. [7] [6] This technique of hiding encoded announcements in letters was not uncommon at the time.
The extreme crescent phase of Venus can be seen without a telescope by those with exceptionally acute eyesight, at the limit of human perception. The angular resolution of the naked eye is about 1 minute of arc (60 seconds). The apparent disk of Venus' extreme crescent measures between 60.2 and 66 seconds of arc, [8] depending on the distance from Earth.
Mesopotamian priest-astronomers described Ishtar (Venus) in cuneiform text as having horns which has been interpreted as indicating observation of a crescent. However, other Mesopotamian deities were depicted with horns, so the phrase could have been simply a symbol of divinity. [1]
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory: vestiges of these are still found in astrology, a discipline long interwoven with public and governmental astronomy. It was not completely separated in Europe during the Copernican Revolution starting in 1543. In some cultures, astronomical data was used for astrological prognostication.
Tycho Brahe, generally called Tycho for short, was a Danish astronomer, known for his comprehensive and unprecedentedly accurate astronomical observations. He was known during his lifetime as an astronomer, astrologer, and alchemist. He was the last major astronomer before the invention of the telescope.
In astronomy, the geocentric model is a superseded description of the Universe with Earth at the center. Under most geocentric models, the Sun, Moon, stars, and planets all orbit Earth. The geocentric model was the predominant description of the cosmos in many European ancient civilizations, such as those of Aristotle in Classical Greece and Ptolemy in Roman Egypt.
In the Hipparchian, Ptolemaic, and Copernican systems of astronomy, the epicycle was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets. In particular it explained the apparent retrograde motion of the five planets known at the time. Secondarily, it also explained changes in the apparent distances of the planets from the Earth.
Sidereus Nuncius is a short astronomical treatise published in Neo-Latin by Galileo Galilei on March 13, 1610. It was the first published scientific work based on observations made through a telescope, and it contains the results of Galileo's early observations of the imperfect and mountainous Moon, of hundreds of stars not visible to the naked eye in the Milky Way and in certain constellations, and of the Medicean Stars that appeared to be circling Jupiter.
Simon Marius was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but spent most of his life in the city of Ansbach. He is most known for being among the first observers of the four largest moons of Jupiter, and his publication of his discovery led to charges of plagiarism.
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms object and body are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound, contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, which may consist of multiple bodies or even other objects with substructures.
Heliocentrism is the astronomical model in which the Earth and planets revolve around the Sun at the center of the universe. Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center. The notion that the Earth revolves around the Sun had been proposed as early as the third century BC by Aristarchus of Samos, who had been influenced by a concept presented by Philolaus of Croton. In the 5th century BC the Greek Philosophers Philolaus and Hicetas had the thought on different occasions that the Earth was spherical and revolving around a "mystical" central fire, and that this fire regulated the universe. In medieval Europe, however, Aristarchus' heliocentrism attracted little attention—possibly because of the loss of scientific works of the Hellenistic period.
The Dialogue Concerning the Two Chief World Systems is a 1632 Italian-language book by Galileo Galilei comparing the Copernican system with the traditional Ptolemaic system. It was translated into Latin as Systema cosmicum in 1635 by Matthias Bernegger. The book was dedicated to Galileo's patron, Ferdinando II de' Medici, Grand Duke of Tuscany, who received the first printed copy on February 22, 1632.
The Tychonic system is a model of the Universe published by Tycho Brahe in the late 16th century, which combines what he saw as the mathematical benefits of the Copernican system with the philosophical and "physical" benefits of the Ptolemaic system. The model may have been inspired by Valentin Naboth and Paul Wittich, a Silesian mathematician and astronomer. A similar model was implicit in the calculations more than a century earlier by Nilakantha Somayaji of the Kerala school of astronomy and mathematics.
The Copernican Revolution was the paradigm shift from the Ptolemaic model of the heavens, which described the cosmos as having Earth stationary at the center of the universe, to the heliocentric model with the Sun at the center of the Solar System. This revolution consisted of two phases; the first being extremely mathematical in nature and the second phase starting in 1610 with the publication of a pamphlet by Galileo. Beginning with the publication of Nicolaus Copernicus’s De revolutionibus orbium coelestium, contributions to the “revolution” continued until finally ending with Isaac Newton’s work over a century later.
The Moon is the largest natural satellite of and the closest major astronomical object to Earth. The Moon may be observed by using a variety of optical instruments, ranging from the naked eye to large telescopes. The Moon is the only celestial body upon which surface features can be discerned with the unaided eyes of most people.
Copernican heliocentrism is the astronomical model developed by Nicolaus Copernicus and published in 1543. This model positioned the Sun at the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular paths, modified by epicycles, and at uniform speeds. The Copernican model displaced the geocentric model of Ptolemy that had prevailed for centuries, which had placed Earth at the center of the Universe.
Paul Wittich was a German mathematician and astronomer whose Capellan geoheliocentric model, in which the inner planets Mercury and Venus orbit the Sun but the outer planets Mars, Jupiter and Saturn orbit the Earth, may have directly inspired Tycho Brahe's more radically heliocentric geoheliocentric model in which all the 5 known primary planets orbited the Sun, which in turn orbited the stationary Earth.
Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.
Galileo di Vincenzo Bonaiuti de' Galilei, commonly referred to as Galileo Galilei or simply Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a polymath. He was born in the city of Pisa, then part of the Duchy of Florence. Galileo has been called the father of observational astronomy, modern-era classical physics, the scientific method, and modern science.
The center of the Universe is a concept that lacks a coherent definition in modern astronomy; according to standard cosmological theories on the shape of the universe, it has no center.
Venus has an orbit with a semi-major axis of 0.723 au, and an eccentricity of 0.007. The low eccentricity and comparatively small size of its orbit give Venus the least range in distance between perihelion and aphelion of the planets: 1.46 million km. The planet orbits the Sun once every 225 days and travels 4.54 au in doing so, giving an average orbital speed of 35 km/s (78,000 mph).
Jacques du Chevreul was a French mathematician, astronomer, and philosopher.
The historical models of the Solar System began during prehistoric periods and are updated to this day. The models of the Solar System throughout history were first represented in the early form of cave markings and drawings, calendars and astronomical symbols. Then books and written records became the main source of information that expressed the way the people of the time thought of the Solar System.
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