Heliocentrism

Jai Ganesh · 2023-11-05 16:40:05

Heliocentrism

Gist

Heliocentrism is the astronomical model in which the Earth and planets revolve around the Sun at the center of the Solar system. - The word "helios" in Greek means "sun." -Heliocentric means that the sun is at the center . -A heliocentric system is one in which the planets revolve around a fixed sun.

Summary

Heliocentrism is a cosmological model in which the Sun is assumed to lie at or near a central point (e.g., of the solar system or of the universe) while the Earth and other bodies revolve around it. In the 5th century BC the Greek philosophers Philolaus and Hicetas speculated separately that the Earth was a sphere revolving daily around some mystical “central fire” that regulated the universe. Two centuries later, Aristarchus of Samos extended this idea by proposing that the Earth and other planets moved around a definite central object, which he believed to be the Sun.

The heliocentric, or Sun-centred, model of the solar system never gained wide support because its proponents could not explain why the relative positions of the stars seemed to remain the same despite the Earth’s changing viewpoints as it moved around the Sun. In the 2nd century AD, Claudius Ptolemy of Alexandria suggested that this discrepancy could be resolved if it were assumed that the Earth was fixed in position, with the Sun and other bodies revolving around it. As a result, Ptolemy’s geocentric (Earth-centred) system dominated scientific thought for some 1,400 years.

In 1444 Nicholas of Cusa again argued for the rotation of the Earth and of other heavenly bodies, but it was not until the publication of Nicolaus Copernicus’s De revolutionibus orbium coelestium libri VI (“Six Books Concerning the Revolutions of the Heavenly Orbs”) in 1543 that heliocentrism began to be reestablished. Galileo Galilei’s support of this model resulted in his famous trial before the Inquisition in 1633.

Details

Heliocentrism (also known as the Heliocentric model) is a superseded astronomical model in which the Earth and planets revolve around the Sun at the center of the universe.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 (c. 470 – 385 BC). 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.

It was not until the sixteenth century that a mathematical model of a heliocentric system was presented by the Renaissance mathematician, astronomer, and Catholic cleric, Nicolaus Copernicus, leading to the Copernican Revolution. In the following century, Johannes Kepler introduced elliptical orbits, and Galileo Galilei presented supporting observations made using a telescope.

With the observations of William Herschel, Friedrich Bessel, and other astronomers, it was realized that the Sun, while near the barycenter of the Solar System, was not at any center of the universe.

Ancient and medieval astronomy

While the sphericity of the Earth was widely recognized in Greco-Roman astronomy from at least the 4th century BC, the Earth's daily rotation and yearly orbit around the Sun was never universally accepted until the Copernican Revolution.

While a moving Earth was proposed at least from the 4th century BC in Pythagoreanism, and a fully developed heliocentric model was developed by Aristarchus of Samos in the 3rd century BC, these ideas were not successful in replacing the view of a static spherical Earth, and from the 2nd century AD the predominant model, which would be inherited by medieval astronomy, was the geocentric model described in Ptolemy's Almagest.

The Ptolemaic system was a sophisticated astronomical system that managed to calculate the positions for the planets to a fair degree of accuracy. Ptolemy himself, in his Almagest, says that any model for describing the motions of the planets is merely a mathematical device, and since there is no actual way to know which is true, the simplest model that gets the right numbers should be used. However, he rejected the idea of a spinning Earth as absurd as he believed it would create huge winds. Within his model the distances of the Moon, Sun, planets and stars could be determined by treating orbits' celestial spheres as contiguous realities, which gave the stars' distance as less than 20 Astronomical Units, a regression, since Aristarchus of Samos's heliocentric scheme had centuries earlier necessarily placed the stars at least two orders of magnitude more distant.

Problems with Ptolemy's system were well recognized in medieval astronomy, and an increasing effort to criticize and improve it in the late medieval period eventually led to the Copernican heliocentrism developed in Renaissance astronomy.

Modern science:

William Herschel's heliocentrism

In 1783, amateur astronomer William Herschel attempted to determine the shape of the universe by examining stars through his handmade telescopes. Herschel was the first to propose a model of the universe based on observation and measurement. At that time, the dominant assumption in cosmology was that the Milky Way was the entire universe, an assumption that has since been proven wrong with observations. Herschel concluded that it was in the shape of a disk, but assumed that the Sun was in the center of the disk, making the model heliocentric.

Seeing that the stars belonging to the Milky Way appeared to encircle the Earth, Herschel carefully counted stars of given apparent magnitudes, and after finding the numbers were the same in all directions, concluded Earth must be close to the center of the Milky Way. However, there were two flaws in Herschel's methodology: magnitude is not a reliable index to the distance of stars, and some of the areas that he mistook for empty space were actually dark, obscuring nebulae that blocked his view toward the center of the Milky Way.

The Herschel model remained relatively unchallenged for the next hundred years, with minor refinements. Jacobus Kapteyn introduced motion, density, and luminosity to Herschel's star counts, which still implied a near-central location of the Sun.

Replacement with galactocentrism and acentrism

Already in the early 19th century, Thomas Wright and Immanuel Kant speculated that fuzzy patches of light called nebulae were actually distant "island universes" consisting of many stellar systems. The shape of the Milky Way galaxy was expected to resemble such "islands universes."

However, "scientific arguments were marshalled against such a possibility," and this view was rejected by almost all scientists until the early 20th century, with Harlow Shapley's work on globular clusters and Edwin Hubble's measurements in 1924. After Shapley and Hubble showed that the Sun is not the center of the universe, cosmology moved on from heliocentrism to galactocentrism, which states that the Milky Way is the center of the universe.

Hubble's observations of redshift in light from distant galaxies indicated that the universe was expanding and acentric. As a result, soon after galactocentrism was formulated, it was abandoned in favor of the Big Bang model of the acentric expanding universe. Further assumptions, such as the Copernican principle, the cosmological principle, dark energy, and dark matter, eventually lead to the current model of cosmology, Lambda-CDM.

Special relativity and the "center"

The concept of an absolute velocity, including being "at rest" as a particular case, is ruled out by the principle of relativity, also eliminating any obvious "center" of the universe as a natural origin of coordinates. Even if the discussion is limited to the Solar System, the Sun is not at the geometric center of any planet's orbit, but rather approximately at one focus of the elliptical orbit. Furthermore, to the extent that a planet's mass cannot be neglected in comparison to the Sun's mass, the center of gravity of the Solar System is displaced slightly away from the center of the Sun. (The masses of the planets, mostly Jupiter, amount to 0.14% of that of the Sun.) Therefore, a hypothetical astronomer on an extrasolar planet would observe a small "wobble" in the Sun's motion.

Modern use of geocentric and heliocentric

In modern calculations, the terms "geocentric" and "heliocentric" are often used to refer to reference frames. In such systems the origin in the center of mass of the Earth, of the Earth–Moon system, of the Sun, of the Sun plus the major planets, or of the entire Solar System, can be selected. Right ascension and declination are examples of geocentric coordinates, used in Earth-based observations, while the heliocentric latitude and longitude are used for orbital calculations. This leads to such terms as "heliocentric velocity" and "heliocentric angular momentum". In this heliocentric picture, any planet of the Solar System can be used as a source of mechanical energy because it moves relatively to the Sun. A smaller body (either artificial or natural) may gain heliocentric velocity due to gravity assist – this effect can change the body's mechanical energy in heliocentric reference frame (although it will not changed in the planetary one). However, such selection of "geocentric" or "heliocentric" frames is merely a matter of computation. It does not have philosophical implications and does not constitute a distinct physical or scientific model. From the point of view of general relativity, inertial reference frames do not exist at all, and any practical reference frame is only an approximation to the actual space-time, which can have higher or lower precision. Some forms of Mach's principle consider the frame at rest with respect to the distant masses in the universe to have special properties.

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#1 2023-11-05 16:40:05

Heliocentrism

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