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HIPPARCHUS

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Bianca
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« Reply #15 on: August 17, 2007, 07:27:22 am »








His star map was thoroughly modified as late as 1,000 years later in 964 by Al Sufi and 1,500 years later (1437) by Ulugh Beg. Later, Halley would use his star catalogue to discover proper motions as well.The system of celestial coordinates used in Hipparchus's star catalog is not known. Since Ptolemy's copy in the Almagest is given in ecliptical coordinates, that system would seem the most likely; although there is evidence that both ecliptic coordinates and equatorial coordinates were used in the original observations.

Brightness of stars

Hipparchus had in 134 BC ranked stars in six magnitude classes according to their brightness: he assigned the value of 1 to the twenty brightest stars, to weaker ones a value of 2, and so forth to the stars with a class of 6, which can be barely seen with the naked eye. This scheme was later adopted by Ptolemy and a similar system is still in use today.
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« Reply #16 on: August 17, 2007, 07:28:45 am »






Precession of the equinoxes (146 BC-130 BC)

Hipparchus is perhaps most famous for having been the first to measure the precession of the equinoxes. There is some suggestion that the Babylonians may have known about precession, but it appears that Hipparchus was the first to really understand it and measure it. According to al-Battani, Chaldean astronomers had distinguished the tropical and sidereal year. He stated that they had, around 330 BC, an estimation for the length of the sidereal year to be SK = 365 days 6 hours 11 min (= 365.258 days) with an error of (about) 2 min. This phenomenon was probably also known to Kidinnu around 314 BC. Yu Xi (fourth century) was the first Chinese astronomer to mention precession.

Hipparchus and his predecessors mostly used simple instruments for astronomical calculations, such as the gnomon, astrolabe, armillary sphere, etc.

.Additionally, as the first in history to correctly explain this with retrogradical movement of vernal point „ over the ecliptic for about 45", 46" or 47" (36" or 3/4' according to Ptolemy) per annum (today's value is 50.29"), he showed the Earth's axis is not fixed in space. By comparing his own measurements of the position of the equinoxes to the star Spica during a lunar eclipse at the time of equinox with those of Euclid's contemporaries (Timocharis of Alexandria (ca. 320 BC - 260 BC), Aristyllus 150 years earlier, the records of Chaldean astronomers (especially Kidinnu's records), and observations of a temple in Thebes, Egypt, that was built around 2000 BC) he still later observed that the equinox had moved 2ƒ relative to Spica. He also noticed this motion in other stars. He obtained a value of not less than 1ƒ in a century. The modern value is 1ƒ in 72 years.

After him many Greek and Arab astronomers had confirmed this phenomenon. Ptolemy compared his catalogue with those of Aristyllus, Timocharis, Hipparchus and the observations of Agrippa and Menelaus of Alexandria from the early 1st century and he finally confirmed Hipparchus' empirical fact that the poles of the celestial equator in one Platonic year (approximately 25,777 sidereal years) encircle the ecliptical pole. The diameter of this circle is equal to the inclination of ecliptic relative to the celestial equator. The equinoctial points in this time traverse the whole ecliptic and they move 1ƒ in a century. This velocity is equal to that calculated by Hipparchus. Because of these accordances, Delambre, P. Tannery and other French historians of astronomy had wrongly jumped to conclusions that Ptolemy recorded his star catalogue from Hipparchus' with an ordinary extrapolation. It was not known until 1898 when Marcel Boll and others had found that Ptolemy's catalogue differs from Hipparchus' not only in the number of stars but in other respects.

This phenomenon was named by Ptolemy just because the vernal point „ leads the Sun. In Latin praecesse means "to overtake" or "to outpass", and today also means to twist or to turn. Its own name shows this phenomenon was discovered before its theoretical explanation, otherwise it would have been given a better term. Many later astronomers, physicists and mathematicians had occupied themselves with this problem, practically and theoretically. The phenomenon itself had opened many new promising solutions in several branches of celestial mechanics: Thabit ibn Qurra's theory of trepidation and oscillation of equinoctial points, Isaac Newton's general gravitational law (which had explained it in full), Leonhard Euler's kinematic equations and Joseph Lagrange's equations of motion, Jean d'Alembert's dynamical theory of the movement of a rigid body, some algebraic solutions for special cases of precession, John Flamsteed's and James Bradley's difficulties in the making of precise telescopic star catalogues, Friedrich Bessel's and Simon Newcomb's measurements of precession, and finally the precession of perihelion in Albert Einstein's general theory of relativity.


http://www.crystalinks.com/hipparchus.html
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« Reply #17 on: September 14, 2007, 12:38:34 pm »


A guy vacationing in Naples has stumbled across one of the most desperately sought pieces of ancient scholarship, long thought lost forever when the great Library of Alexandria Egypt was destroyed around 400 AD.

Apparently, it had been right in front of millions of tourists for centuries.

A statue of Atlas carrying the Universe on his shoulders turns out to have used the lost celestial globe of Hipparchus, the Greek astronomer who first discovered the precession of Earth’s axis, observed a nova, precisely calculated the length of the year, and invented the stellar brightness scale used today.

And he also made this newly-rediscovered, amazingly accurate star map, complete with celestial equator, ecliptic, and Tropics of Cancer and Capricorn.
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« Reply #18 on: September 14, 2007, 12:45:56 pm »








                            ANCIENT ASTRONOMER'S WORK FOUND ON ROMAN STATUE






From: http://www.swissinfo.org/sen/swissinfo.html?siteSect=143&sid=5461267

SAN DIEGO (Reuters) - A Roman statue of Atlas -- the mythical titan who carried the heavens on his shoulders -- holds clues to the long-lostwork of the ancient astronomer Hipparchus, an astronomical historian says.

The statue in question is known as the Farnese Atlas, a 2.1 metre tall marble work which resides in the Farnese Collection in the National Archeological Museum in Naples, Italy.

What makes it important to scientists is not the titan's muscular form but the globe he supports: carved constellations adorn its surface in exactly the locations Hipparchus would have seen in his day, suggesting that the sculptor based the globe on the ancient astronomer's star catalogue, which no modern eyes have seen.

"There are really very few instances where lost ancient secrets or wisdom are ever actually found," said Bradley Schaefer of LouisianaState University. "Here is a real case where rather well-known lost ancient wisdom has been discovered."

Hipparchus, who flourished around 140-125 BC, is believed to have been one of the world's first path-breaking astronomers. Among other innovations, he put together the first comprehensive list of the hundreds of stars he observed, known as a star catalogue.

This catalogue no longer exists, and previously the only evidence for it came from references made to it by astronomers who followed Hipparchus, Schaefer said.

Another Hipparchus invention -- the idea of precession, which is the slow movement of the stars and constellations across the sky in relation to the celestial equator -- led Schaefer to believe that Atlas's globe referred to Hipparchus's star catalogue.

An analysis of the positions of the constellation figures on Atlas's globe allowed Schaefer to date the work to 125 BC, plus or minus 55 years. This would have been within the range when Hipparchus would have been working.

Other theories about who wrote the star catalogue include observers who were either too early -- including a poet writing around 275 BC and an Assyrian observer around 1130 BC -- or too late. This includes the astronomer Ptolemy, writing in 128 AD.

Reuters
 
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« Reply #19 on: October 20, 2007, 08:38:45 pm »








                         T H E   A N T I K Y T H E R A   M E C H A N I S M




Decoding an ancient computer

November 30, 2006
 
A group of scientists from the U.K. and Greece led by Mike Edmunds, an astronomer from the University of Cardiff, has unlocked a code more ancient and mysterious than those found in Foucault's Pendulum or The Da Vinci Code. The team has deciphered the Antikythera Mechanism, an ancient computer named for the Greek island where it was discovered.


The top image is the main fragment of the original bronze mechanism. Below is the scientists' computer-generated re-creation.

Copyright/credit Jo Marchant, Nature/Copyright of the Antikythera Mechanism Research Project


Credit: Nature/Antikythera Mechanism Research Pr
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« Reply #20 on: October 20, 2007, 08:42:10 pm »








The Antikythera Mechanism was found by divers in 1901 off the coast of Antikythera, a Greek island 18 miles north of Crete. A rough replica of the device was eventually constructed and archeologists guessed that it was an astronomical calculator. But the inner workings and the device's true nature went unknown for 100 years. Now, several physical factors and the device's reference to Hipparchos, place the mechanism between 140-200 B.C., and a complete computer model of the device (shown here) has been constructed, according to the group's findings published in the November 30, 2006, issue of Nature.

Credit: Copyright of the Antikythera Mechanism Research Project
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« Reply #21 on: October 20, 2007, 08:45:42 pm »








High-tech x-rays and imaging methods have shed new light on the mystery object, enabling scientists to reconstruct the device's internal components with computer generated imagery. They were also able to read its "instruction manual." The findings are being discussed at the "Decoding the Antikythera Mechanism--Science and Technology in Ancient Greece" conference in Athens, Greece, on Thursday and Friday.
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« Reply #22 on: October 20, 2007, 08:48:22 pm »








By using tomography developed by British x-ray tech company X-Tek on the Antikythera Mechanism's remaining fragments, scientists were able to determine the placement of the inner gears.


Credit: X-Tek/NaturE
« Last Edit: October 20, 2007, 08:51:43 pm by Bianca2001 » Report Spam   Logged

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« Reply #23 on: October 20, 2007, 08:53:21 pm »









The Antikythera could be considered the first analog computer. The team of experts from the U.K. and Greece discovered that its system of dials and more than 30 gears is more complex than those found in medieval clocks, according to the Nature article. It suggests that the Hellenic people were much farther along technologically than scientists, historians and archeologists had assumed.

The device, in other words, is at least 1,000 years ahead of its time.

So with one mystery solved, another one has presented itself. How is it that such an invention had no historical effect? What stopped the technology from being spread and perpetuated throughout the rest of the world?


Credit: Copyright of the Antikythera Mechanism Research Project
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« Reply #24 on: October 20, 2007, 08:56:14 pm »









While parts of the Antikythera Mechanism inscription had been deciphered, many parts remained unreadable. A Polynomia Texture Maps (PTM) machine, constructed specifically for the Antikythera Mechanism, was developed by Hewlett-Packard Laboratories and brought on location to Greece. PTM are made from a series of reflected light images under varying lighting conditions. This allows multiple views of a textured surface to be seen.

The scientific team used the "PTM Dome" to more clearly "see" the device's surfaces, which included minute inscriptions.


Credit: X-Tek
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« Reply #25 on: October 20, 2007, 08:58:42 pm »









The inscriptions on the Antikythera Mechanism have been deciphered to reveal theories for ancient planetary positions. The mechanism was used to predict and calculate lunar and solar eclipses on the basis of Babylonian arithmetic-progression cycles, according to the team's report. The mechanism also calculates lunar positions based on theories by the famous Greek astronomer Hipparchos for deciphering the Moon's elliptical orbit. The machine's ability to calculate sophisticated astronomical knowledge of the Moon's unusual orbit surprised the scientists. (Click here to watch Java Applet movies on HP Labs' site of the Antikythera Mechanism.)

--Text compiled by CNET News.com's Candace Lombardi

Credit: X-Tek


http://www.news.com/2300-11397_3-6139721-7.html?tag=ne.gall.pg
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