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37-688: (Redirected from Earth-orbit ) Earth orbit may refer to: Earth's orbit , the orbit of the Earth around the Sun Low Earth orbit , an orbit around the Earth Geocentric orbit , an orbit around the Earth See also [ edit ] Earth Orbiter 1 , a shuttle simulator Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with

74-419: A book consisting of certain hypotheses , wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the "universe" just mentioned. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun on the circumference of a circle, the sun lying in the middle of the orbit , and that the sphere of the fixed stars, situated about

111-452: A lunar eclipse . The first of these consisted of the time that it took for the Earth's shadow to fully encompass the Moon, along with how long the Moon remained within the shadow. This was used to estimate the angular radius of the shadow. From there, using the width of the cone that was created by the shadow in relation to the Moon, he determined that it was twice the diameter of the Moon at

148-463: A Sun or Moon diameter every 12 hours). Earth's orbital speed averages 29.78 km/s (19 mi/s; 107,208 km/h; 66,616 mph), which is fast enough to cover the planet's diameter in 7 minutes and the distance to the Moon in 4 hours. The point towards which the Earth in its solar orbit is directed at any given instant is known as the "apex of the Earth's way". From a vantage point above

185-498: A misinterpretation of which unit of measure was meant by a Greek term in the text of Aristarchus. Aristarchus claimed that at half moon ( first or last quarter moon ), the angle between the Sun and Moon was 87°. He may have proposed 87° as a lower bound, since gauging the lunar terminator 's deviation from linearity to one degree of accuracy is beyond the unaided human ocular limit (which is about three arcminutes of accuracy). Aristarchus

222-487: A work in which Aristarchus advanced the heliocentric model as an alternative hypothesis to geocentrism: You are now aware ['you' being King Gelon] that the "universe" is the name given by most astronomers to the sphere the centre of which is the centre of the earth, while its radius is equal to the straight line between the centre of the sun and the centre of the earth. This is the common account (τὰ γραφόμενα) as you have heard from astronomers. But Aristarchus has brought out

259-469: Is an ellipse with the Earth–Sun barycenter as one focus with a current eccentricity of 0.0167. Since this value is close to zero, the center of the orbit is relatively close to the center of the Sun (relative to the size of the orbit). As seen from Earth, the planet's orbital prograde motion makes the Sun appear to move with respect to other stars at a rate of about 1° eastward per solar day (or

296-486: Is head of the Stoics , a sun worshipper , and opposed to heliocentrism. In the manuscript of Plutarch's text, Aristarchus says Cleanthes should be charged with impiety. Ménage's version, published shortly after the trials of Galileo and Giordano Bruno , transposes an accusative and nominative so that it is Aristarchus who is purported to be impious. The resulting misconception of an isolated and persecuted Aristarchus

333-430: Is known to have studied light and vision as well. Using correct geometry , but the insufficiently accurate 87° datum , Aristarchus concluded that the Sun was between 18 and 20 times farther away from the Earth than the Moon. (The correct value of this angle is close to 89° 50', and the Sun's distance is approximately 400 times that of the Moon.) The implicit inaccurate solar parallax of slightly under three degrees

370-427: Is opposed to geocentrism , which placed the Earth at the center. Aristarchus of Samos already proposed a heliocentric model in the third century BC. In the sixteenth century, Nicolaus Copernicus ' De revolutionibus presented a full discussion of a heliocentric model of the universe in much the same way as Ptolemy had presented his geocentric model in the second century. This " Copernican Revolution " resolved

407-462: Is still promulgated. According to Plutarch, while Aristarchus postulated heliocentrism only as a hypothesis, Seleucus of Seleucia , a Hellenistic astronomer who lived a century after Aristarchus, maintained it as a definite opinion and gave a demonstration of it, but no full record of the demonstration has been found. In his Naturalis Historia , Pliny the Elder later wondered whether errors in

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444-493: Is unlikely that Copernicus was aware that it was a heliocentric theory. Aristarchus estimated the sizes of the Sun and Moon as compared to Earth's size. He also estimated the distances from the Earth to the Sun and Moon. He is considered one of the greatest astronomers of antiquity along with Hipparchus . The original text has been lost, but a reference in a book by Archimedes , entitled The Sand Reckoner ( Archimedis Syracusani Arenarius & Dimensio Circuli ), describes

481-585: The Sun at an average distance of 149.60 million km (92.96 million mi), or 8.317 light-minutes , in a counterclockwise direction as viewed from above the Northern Hemisphere . One complete orbit takes 365.256  days (1 sidereal year ), during which time Earth has traveled 940 million km (584 million mi). Ignoring the influence of other Solar System bodies, Earth's orbit , also called Earth's revolution ,

518-416: The summer solstice of 280 BC. Along with his contributions to the heliocentric model, as reported by Vitruvius , he created two separate sundials : one that is a flat disc; and one hemispherical. Aristarchus was influenced by the concept presented by Philolaus of Croton (c. 470 – 385 BC) of a fire at the center of the universe, but Aristarchus identified the "central fire" with the Sun and he arranged

555-567: The Earth moves around the Sun. Since stellar parallax is only detectable with telescopes , his accurate speculation was unprovable at the time. It is a common misconception that the heliocentric view was considered sacrilegious by the contemporaries of Aristarchus. Lucio Russo traces this to Gilles Ménage 's printing of a passage from Plutarch 's On the Apparent Face in the Orb of the Moon , in which Aristarchus jokes with Cleanthes , who

592-433: The Sun than does the northern over the course of a year. However, this effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of surface covered by water in the southern hemisphere. The Hill sphere ( gravitational sphere of influence) of the Earth is about 1,500,000 kilometers (0.01 AU ) in radius, or approximately four times

629-562: The Sun. The only known work attributed to Aristarchus, On the Sizes and Distances of the Sun and Moon , is based on a geocentric worldview. Historically, it has been read as stating that the angle subtended by the Sun's diameter is two degrees, but Archimedes states in The Sand Reckoner that Aristarchus had a value of half a degree, which is much closer to the average value of 32' or 0.53 degrees. The discrepancy may come from

666-490: The average distance to the Moon. This is the maximal distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects orbiting the Earth must be within this radius, otherwise, they may become unbound by the gravitational perturbation of the Sun. The following diagram illustrates the positions and relationship between the lines of solstices, equinoxes, and apsides of Earth's elliptical orbit. The six Earth images are positions along

703-403: The diameter of the Moon is roughly one-third of the Earth's diameter. In order to estimate the size of the Sun, Aristarchus considered the proportion of the Sun's distance to Earth in comparison to the Moon's distance from Earth, which was found to be roughly 18 to 20 times the length. Therefore, the size of the Sun is around 19 times wider than the Moon, making it approximately six times wider than

740-531: The direction of the Earth's axial tilt) results in the seasons . By astronomical convention, the four seasons are determined by the solstices (the two points in the Earth's orbit of the maximum tilt of the Earth's axis, toward the Sun or away from the Sun) and the equinoxes (the two points in the Earth's orbit where the Earth's tilted axis and an imaginary line drawn from the Earth to the Sun are exactly perpendicular to one another). The solstices and equinoxes divide

777-411: The full, non-central eclipse. In addition to this, Aristarchus estimated that the length of the shadow extended around 2.4 times the distance of the Moon from the Earth. Using these calculations, along with his estimated distances of the Sun from the Earth and Moon from the Earth, he created a triangle. Employing geometry similar to that he had already used for the distances, he was able to determine that

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814-620: The initial position of the Earth today would make it impossible to predict where Earth would be in its orbit in just over 100 million years' time. Modeling the Solar System is a subject covered by the n-body problem . Aristarchus of Samos He likely moved to Alexandria , and he was a student of Strato of Lampsacus , who later became the third head of the Peripatetic School in Greece . According to Ptolemy, he observed

851-477: The issue of planetary retrograde motion by arguing that such motion was only perceived and apparent. According to historian Jerry Brotton , "Although Copernicus's groundbreaking book ... had been [printed more than] a century earlier, [the Dutch mapmaker] Joan Blaeu was the first mapmaker to incorporate his revolutionary heliocentric theory into a map of the world." Because of Earth's axial tilt (often known as

888-543: The north pole is tilted away from the Sun, the reverse is true and the weather is generally cooler. North of the Arctic Circle and south of the Antarctic Circle , an extreme case is reached in which there is no daylight at all for part of the year, and continuous daylight during the opposite time of year. This is called polar night and midnight sun , respectively. This variation in the weather (because of

925-511: The north pole of either the Sun or Earth, Earth would appear to revolve in a counterclockwise direction around the Sun. From the same vantage point, both the Earth and the Sun would appear to rotate also in a counterclockwise direction about their respective axes. Heliocentrism is the scientific model that first placed the Sun at the center of the Solar System and put the planets, including Earth, in its orbit. Historically, heliocentrism

962-455: The northern hemisphere, where it is colder when the Earth is closest to the sun and warmer when it is furthest away. The changing Earth-Sun distance results in an increase of about 7% in total solar energy reaching the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, the southern hemisphere receives slightly more energy from

999-410: The obliquity of the ecliptic ), the inclination of the Sun's trajectory in the sky (as seen by an observer on Earth's surface) varies over the course of the year. For an observer at a northern latitude, when the north pole is tilted toward the Sun the day lasts longer and the Sun appears higher in the sky. This results in warmer average temperatures, as additional solar radiation reaches the surface. When

1036-716: The orbital ellipse, which are sequentially the perihelion (periapsis—nearest point to the Sun) on anywhere from January 2 to January 5, the point of March equinox on March 19, 20, or 21, the point of June solstice on June 20, 21, or 22, the aphelion (apoapsis—the farthest point from the Sun) on anywhere from July 3 to July 5, the September equinox on September 22, 23, or 24, and the December solstice on December 21, 22, or 23. Mathematicians and astronomers (such as Laplace , Lagrange , Gauss , Poincaré , Kolmogorov , Vladimir Arnold , and Jürgen Moser ) have searched for evidence for

1073-403: The other planets in their correct order of distance around the Sun. Like Anaxagoras before him, Aristarchus suspected that the stars were just other bodies like the Sun, albeit farther away from Earth. His astronomical ideas were often rejected in favor of the geocentric theories of Aristotle and Ptolemy . Nicolaus Copernicus knew that Aristarchus had a 'moving Earth' theory, although it

1110-407: The predictions about the heavens could be attributed to a displacement of the Earth from its central position. Pliny and Seneca referred to the retrograde motion of some planets as an apparent (unreal) phenomenon, which is an implication of heliocentrism rather than geocentrism. Still, no stellar parallax was observed, and Plato , Aristotle , and Ptolemy preferred the geocentric model that

1147-400: The same centre as the sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the centre of the sphere bears to its surface. Aristarchus suspected the stars were other suns that are very far away, and that in consequence there was no observable parallax , that is, a movement of the stars relative to each other as

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1184-510: The southern hemisphere are the reverse of those in the northern hemisphere (e.g. the northern summer solstice is at the same time as the southern winter solstice). In modern times, Earth's perihelion occurs around January 3, and the aphelion around July 4. In other words, the Earth is closer to the Sun in January, and further away in July, which might seem counter-intuitive to those residing in

1221-426: The stability of the planetary motions, and this quest led to many mathematical developments and several successive "proofs" of stability for the Solar System. By most predictions, Earth's orbit will be relatively stable over long periods. In 1989, Jacques Laskar 's work indicated that Earth's orbit (as well as the orbits of all the inner planets) can become chaotic and that an error as small as 15 meters in measuring

1258-472: The title Earth orbit . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Earth_orbit&oldid=1239874870 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Earth%27s orbit Earth orbits

1295-405: The year up into four approximately equal parts. In the northern hemisphere winter solstice occurs on or about December 21; summer solstice is near June 21; spring equinox is around March 20, and autumnal equinox is about September 23. The effect of the Earth's axial tilt in the southern hemisphere is the opposite of that in the northern hemisphere, thus the seasons of the solstices and equinoxes in

1332-502: Was believed throughout the Middle Ages . The heliocentric theory was revived by Copernicus , after which Johannes Kepler described planetary motions with greater accuracy with his three laws. Isaac Newton later gave a theoretical explanation based on laws of gravitational attraction and dynamics. After realizing that the Sun was much larger than the Earth and the other planets, Aristarchus concluded that planets revolved around

1369-500: Was used by astronomers up to and including Tycho Brahe , c. AD 1600. Aristarchus pointed out that the Moon and Sun have nearly equal apparent angular sizes, and therefore their diameters must be in proportion to their distances from Earth. In On the Sizes and Distances of the Sun and Moon , Aristarchus discusses the size of the Moon and Sun in relation to the Earth. In order to achieve these measurements and subsequent calculations, he used several key notes made while observing

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