ASTRONOMY AND COSMOLOGY I

A reference to Aristotle is essential in a history of science, though impossible in a few sentences without being banal. This greatest of all Greek philosophers, who flourished in the 4th century BC, exerted an all-encompassing influence on the development of western thought. He introduced the systematic study of logic which he applied to his teachings. In his biological writings he presented a classification system of animals that was not fully replaced until the time of Linnaeus. All branches of knowledge were classified: physics, methaphysics, rhetoric, poetics. His picture of a perfect, unchanging, spherical universe centered on the earth placed a long-lasting damper on western understanding of the workings of the physical world, particularly the motions of the stars and planets. To the four supposed elements making up the universe, earth, water, air, and fire, he added a fifth, invisible element, the ether. This ether, made necessary because "nature abhorrs a vacuum", was an inpalpable fixture for over 2000 years until its existence was disproved by the Michelson-Morley experiment. His teachings, lost to western Europe during the dark ages, were reintroduced after contacts with the Arab world increased. The Scholastics reconciled Christian dogma with Aristotle's ideas, which virtually became dogma in secular learning. This discouraged independent scientific observation, inquiry, and experiment, even though Aristotle himself had been an interested observer of the natural world.

Aristarchus of Samos (3rd century BC) considered the sizes and distances of the sun and the moon, and was the first to try to calculate the distances of these bodies geometrically . Furthermore, he advanced the theory that the sun was at rest at the center of the sphere of fixed stars, and that the earth and planets revolved around the sun. The apparent motion of the stars was due to the daily rotation of the earth. Copernicus was familiar with Aristarchus' theory of the universe, which at the time, however, did not find favor with the ancient philosophers.

Hipparchus (2nd century BC), the greatest astronomer of the ancient world, is thought to have invented the astrolabe. He continued the work of Aristarchus in calculating the distance of the moon by measuring its parallax against the sphere of fixed stars. His result of 30 earth diameters is correct. From his observations he produced the first star catalogue, grading the stars by brightness. He also discovered the precession of the equinoxes.

Zhang Heng (78-139) was a Chinese astronomer, geographer, and mathematician. He constructed a celestial globe, believing that the world was round, "The sky is like a hen's egg, and is as round as a crossbow pellet; the Earth is like the yolk of the egg, lying alone at the centre. The sky is large and the Earth small." He also created a primitive, but very fanciful seismograph. His approximation of pi was the square root of 10.

Ptolemy (2nd century AD) was a famous astronomer, mathematician and geographer whose geocentric view of the universe was dogma in western thought until 1200 years later, when Copernicus was able to offer a competing heliocentric model which accounted just as well for many of its inconsistencies with observations. Ptolemy synthesized and extended the star catalogue of Hipparchus and much of Greek astronomy in his Almagest.

A Chinese astronomer and Buddhist monk of the Tang dynasty, Zhang Sui (683-727), was the first to describe proper stellar motion, or the apparent motion of stars across the plane of the sky relative to more distant stars. In Western astronomy, Edmond Halley is credited with this discovery in 1718 for some stars from Ptolemy's catalogue.

Ulugh Beg (1394-1449) was the grandson of Tamerlane, the Turkish conqueror of a large empire stretching from the Mediterranean to India. While acting as a ruler under his grandfather and father, the prince was an astronomer and builder of observatories in their capital city of Samarkand, where a stellar catalog was produced, the first since Ptolemy's and before Tycho Brahe. Permanent astronomical instruments of huge dimensions were constructed, since telescopes had not yet been invented. The most direct influence of the Samarkand Observatory was some centuries hence on the Indian Maharajah Jai Singh (1686-1743) who constructed five observatories, or Jantar Mantars, as shown on the Jaipur stamp below:

Nicolaus Copernicus (1473-1543), a Polish astronomer, proposed a heliocentric theory of the universe in which the planets orbited the sun, rather than the earth. It marked the end of the world with man and the earth at its center. Ironically, Copernicus appears here on a Vatican stamp for a theory that flew in the face of established religion in his time. Although known portraits of Copernicus are full face, one modern artist's conception shows a thoughtful man in profile. The French stamp shows a picture of the universe as Copernicus envisioned it -- the six known planets circling the sun. Silhouettes of the Polish churches from whose towers Copernicus made his observations are in the foreground. The souvenir sheet on the left shows the Copernican world view from a beautiful celestial atlas made by Andreas Cellarius, Harmonia Macrocosmica, 1661, This planisphere shows the solar system updated from Copernicus' time; the four moons of Jupiter are clearly visible. Venus appears to be obscured by the vertical stamp perforations; on other editions of this work the planets are shown in somewhat shifted positions. This universe is flanked by two figures: at right Copernicus himself, and at left Aristarchus of Samos, the earlier proponent of the heliocentric theory, here lending weight to Copernicus' theory.

Tycho Brahe (1546-1601) was the last and greatest of the naked-eye astronomers, rivalled only perhaps by Hipparchus. His book on his observations of an exploding star, De Nova Stella, gives us the word "nova." His many painstaking observations were passed on to his assistant Kepler, who used them to derive his three laws of planetary motion in a heliocentric universe, while Tycho himself had remained an adherent of the Ptolemaic geocentric world view. For over 20 years Tycho made observations from his castle Uraniborg on the island of Ven, given him as a fief by the king to keep the famed astronomer in Denmark. The layout of the castle was geometric and perfectly aligned with the compass. His instruments, built to his own specifications and design, were large scale to provide greater accuracy than achieved before. The stamps on the right were a joint issue of Denmark and Sweden. One shows a plan of Uraniborg and its grounds, the other, one of Tycho's instruments. On the stamp appears the longest word I have ever seen on a stamp: ekvatotialarmillarinstrument. Identified as a sextant in Scott, it is almost certainly the great equatorial armillary sphere (1585) . It consisted of one single declination circle, 272 cm in diameter, and a semicircle representing the equator, 350 cm in diameter. Full descriptions of all his instruments and the castle can be found on the Official Tycho Brahe Website .

Johannes Kepler (1571-1630) was a German mathematician who is remembered for his three laws of planetary motion, derived empirically from Tycho Brahe's data and observations, describing the solar system with the sun at the focus of elliptic planetary orbits. In his work, he used an early calculating machine (right) invented by his friend Wilhelm Schickard (1592-1635), some 15 years before Pascal built his own. In his writings on conic sections Kepler added the word "focus" to mathematical language.

This colorful Chinese stamp approximates our current view of the solar system, even showing the asteroid belt between the orbits of Mars and Jupiter. It was issued in 1982 to mark a rare alignment of the planets twice during that year, in in March and May. The nine planets clustered into a relatively small fan-shaped area on the same side of the sun, in arcs of 96 and 105 degrees. The average cycle for such an event is 179 years, and the next one is estimated to happen in 2357. This clustering, or conjunction, is also called syzygy, a word worth remembering for a game of Scrabble.

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Sci-Philately: A Selective History of Science on Stamps

Last Modified: 23 February 2006 mn
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	Aristarchus of Samos (3rd century BC) considered the sizes and distances of the sun and the moon, and was the first to try to calculate the distances of these bodies geometrically . Furthermore, he advanced the theory that the sun was at rest at the center of the sphere of fixed stars, and that the earth and planets revolved around the sun. The apparent motion of the stars was due to the daily rotation of the earth. Copernicus was familiar with Aristarchus' theory of the universe, which at the time, however, did not find favor with the ancient philosophers.
	Hipparchus (2nd century BC), the greatest astronomer of the ancient world, is thought to have invented the astrolabe. He continued the work of Aristarchus in calculating the distance of the moon by measuring its parallax against the sphere of fixed stars. His result of 30 earth diameters is correct. From his observations he produced the first star catalogue, grading the stars by brightness. He also discovered the precession of the equinoxes.
	Zhang Heng (78-139) was a Chinese astronomer, geographer, and mathematician. He constructed a celestial globe, believing that the world was round, "The sky is like a hen's egg, and is as round as a crossbow pellet; the Earth is like the yolk of the egg, lying alone at the centre. The sky is large and the Earth small." He also created a primitive, but very fanciful seismograph. His approximation of pi was the square root of 10.
	Ptolemy (2nd century AD) was a famous astronomer, mathematician and geographer whose geocentric view of the universe was dogma in western thought until 1200 years later, when Copernicus was able to offer a competing heliocentric model which accounted just as well for many of its inconsistencies with observations. Ptolemy synthesized and extended the star catalogue of Hipparchus and much of Greek astronomy in his Almagest.
	A Chinese astronomer and Buddhist monk of the Tang dynasty, Zhang Sui (683-727), was the first to describe proper stellar motion, or the apparent motion of stars across the plane of the sky relative to more distant stars. In Western astronomy, Edmond Halley is credited with this discovery in 1718 for some stars from Ptolemy's catalogue.
	Ulugh Beg (1394-1449) was the grandson of Tamerlane, the Turkish conqueror of a large empire stretching from the Mediterranean to India. While acting as a ruler under his grandfather and father, the prince was an astronomer and builder of observatories in their capital city of Samarkand, where a stellar catalog was produced, the first since Ptolemy's and before Tycho Brahe. Permanent astronomical instruments of huge dimensions were constructed, since telescopes had not yet been invented. The most direct influence of the Samarkand Observatory was some centuries hence on the Indian Maharajah Jai Singh (1686-1743) who constructed five observatories, or Jantar Mantars, as shown on the Jaipur stamp below: