Ancient Astronomy

Wednesday 20 September 2017 - 00:20:42 Posted by  Bobby

A Matter of Life and Death

  All ancient peoples studied the sky, and gave names to the pictures they envisaged in groups of stars. Separated by vast distances and time, many cultures developed similar beliefs: The Babylonians, Greeks, Chinese, Egyptians, and others assigned god-like powers to the stars, planets, and constellations; the Babylonians and Mongols saw the Milky Way as a seam sewing together the two halves of heaven, while the Vikings, Sumerians, and some Native North Americans believed it was a bridge between the living and dead.

  Many early civilizations created calendars to help make decisions about the timing of various activities: religious festivals, planting and harvesting, even wars, were guided by both the regular, and irregular, movements of celestial bodies. Understanding astronomy could be a matter of life and death.

  In high latitudes, the lengthening days of spring forecast the return of the growing season with its promise of continuing life. Near the equator, the changing stars indicated the coming of the monsoon rains and a shift in wind direction, crucial to agricultural and sea trade.

  All the ancients revered the Sun as the primary God. The Babylonian sun-god Shamash provided human society with laws. The Greeks saw Helios (Apollo), god of the Sun, music, poetry, prophecy, and medicine, daily drive his flaming chariot across the sky. Egypt's Amen-Ra protected the human realm: King Akhenaton (c.1500 BCE) claimed that Ra was the only God, making him the first monotheist in recorded history.

The Sun God Apollo

Apollo
  In Greek and Roman mythology, various names are attributed to a Sun God, including Helios, Phoebus, and Apollo. Here we see Apollo represented in the German publication, War habits of the Romans.

 Astronomical Observations

Orion2
  In ancient times, the Egyptians knew that the first appearance of Sirius - the brightest star in the sky - alongside the Morning Sun heralded the imminent annual flooding of the River Nile and the salvation of their parched fields.

  Where the ancient Greeks observed the constellation Orion (The Hunter), the ancient Japanese saw Betlegeuse (top left) and Rigel (bottom right), the two brightest stars, as samurai warriors preparing to fight; they were separated by the three stars between, which the Greeks knew (as we do still) as "Orion's Belt."

  The Egyptian pyramids, and Stonehenge on England's Salisbury Plain (both dating from around 2500 BCE), display through the extreme accuracy of their alignments and comprehensive knowledge of celestial movements over a long period of time, proving that the study of Astronomy was already very advanced. The pillars of Stonehenge (known as sarsen station stones) are arranged to know important events such as solstices and equinoxes, and the site was used by people from near and far for various rites of hope and thanksgiving.

  The Great Pyramid at Giza in Egypt reveals surveying procedures of a very high order. The base, each side of which measures 745 ft (227m), is level to within less than an inch (2.5 cm), while the differences between the pyramids longest and shortest sides is less than 2 inches (5 cm). Its alignment with the cardinal points of the compass is almost perfect, the error being less than 0.02%. Unfortunately, there is nothing left to tell us how its creators were able to make such accurate calculations nor what machines they used.

Chinese Astronomy

Chinesewheel
  Chinese astronomers, studying the stars as long ago as 2100 BCE envisaged 283 constellations. Rather than mythological heroes and beasts, these constellations rebuild scenes from social and regal life. The astronomers also categorized guest stars, which we now know as novae, supernovae, and comets. By the 3rd century BCE they were aware that earth was in motion, and that this motion was responsible for the seasons. They saw the relationship between Earth and the heavens as similar to that between the two parts of an egg, the yolk (Earth) floating on a sea while the white (the heavens) revolved around the North Pole. By the 1st century BCE, they were using the armilary, a sphere with lines showing various celestial trajectories, and had built a number of planetarium observatories.

Calendars

  By the first century CE, the Mayans of South East Mexico were using the "Long Count Calendar," which was an accurate comprehensive method of recording the monthly and annual cycles that form the basis of their political, agricultural, and religious life. Ceremonial buildings - often pyramids - were precisely aligned with compass directions and also, frequently, with special positions of the Sun, Moon, and various constellations. At the equinoxes, for example, the sunlight radiates through small openings in the walls, lighting up sacred areas in a building's interior.
 
  The Babylonians, in what is now Iraq, were the first to divide the year into 360 days, the sky into 360 degrees of Arc, the degree into 60 minutes, and the day into 24 hours, with each hour also divided into 60 parts. Around 700 BCE they produce the extraordinary baked clay artefacts known as the Mal-Apin Tablets, which summarize thousands of years of observations of the motions of stars and planets, and list constellations including Scorpius and Leo.

  In ancient Assyria, Rome, South America, China, and India, a year also consisted of 360 days, divided into 12 months of 30 days. The Egyptian and Mayan calendars featured an undivided 360-day year.

  From a human viewpoint, the Sun, Moon, and planets appear to move in a large circle, passing through the same constellations over the course of a year. The Babylonians invented the 12 signs of the zodiac based on these constellations, the Sun passing through one constellation per month as earth revolved around it. Their system was subsequently adopted in Egypt, Greece, India, and China. The Aztecs later created a similar system, probably independently.

Aztec Solar Calendar

Azteccalendar
  The Aztec solar calendar was carved into this great stone, which is now held in a museum in Mexico. The pre-columbian Aztecs based their calendar on those used throughout ancient Mesoamerica.

Ancient Greece

  Babylonian knowledge reached Greece around the 6th century BCE. But where the Babylonians used their observations of the stars to divine omens (astrology), the Greeks were more concerned with understanding the physical principles that underpin the workings of the universe (astronomy). It is hard to overstate the importance of this difference in emphasis, which mark the beginning of the separation of superstition and science in the quest for knowledge.

  The philosopher - astronomer Thales gained great fame for correctly predicting the solar eclipse of May 25, 585 BCE.

  Democritus (460 - 370 BCE), who correctly predicted the atomic structure of matter, also surmise that the Milky Way galaxy is not a fog of light, as it appears, but comprises stars so faint and numerous that they appear to merge together. How could he in envisage such things, millenia before they were proved? We can only hazard a guess.

  The father of Western philosophical thought, Plato (428 - 348 BCE), also turned his mind to astronomy, contending that Earth was round, and that its motion causes day and night. Plato's empirical, geometry-based methods were a giant step towards astronomy being dealt with in a scientific manner.

  Heraclidus Ponticus (390 - 310 BCE) was the first to deduce that Mercury and Venus are satellites of the Sun, while Heraklides of Pontus (388 - 315 BCE) proposed that Earth spins on its axis.

  Aristotle (384 - 322 BCE) was an unsurpassed genius in the field of astronomy as well as in philosophy, psychology, history, physics, and logic. His observations led him to believe that Earth is spherical, as are the stars and planets - for if earth were not spherical, lunar eclipses would not show a curved outline, nor would the stars changed positions when one traveled north or south.  However, Aristotle also surmised that, because the falling objects are attracted to it, Earth must be at the center of the universe.

  The astronomer and mathematician Eudoxus Cnidus (4th century BCE) outlined a system of 27 crystal concentric spheres, rotating at different speeds on different axes. Celestial bodies embedded in those spheres rotated around the spherical earth. Later Greek astronomers revised this system, but Eudoxus's ideal of perfect circular movements and a geocentric universe was generally accepted in Western astronomical thought until the 17th century. Eudoxus traveled widely; he even studied astronomy with the priests at Heliopolis in Egypt.
 
  The esteemed scholar Aristsarchus of Samos (c. 310 - 230 BCE) proposed that the Sun was much larger than previously believed. Observing that Mercury and Venus never stray too far from the Sun, and that Mars, Jupiter, and Saturn sometimes appear to travel backward across the sky, Aristarchus explained these phenomena by including that Earth and the planets must all revolve around the Sun. He reasoned that the seasons were caused by a tilt of Earth's axis. Aristarchus is also famed for his treatise On The Sizes and Distances of the Sun and Moon, which provides an astounding geometric argument, based on observation, to calculate that the Sun was approximately 20 times as distant from Earth as the Moon, and 20 times the Moon's size. (While the true multiple is about 400 in each case, Aristarchus's reasoning was correct, the error being caused by his lack of accurate instruments.) His ideas, all since proved correct, were too radical to be generally accepted for some 2,000 years.
 
  In 129 BCE, Hipparchus, ancient Greece's  most influential astronomical observer of all, created the first accurate star catalogue of 850 stars visible to the naked eye, and classify them into six different categories of brightness, a system of magnitude that is still in use. Sadly, most published works by Hipparchus have been lost, including an astronomical calendar, & a ray of writings on the subject of optics, astrology, arithmetic, & geology, as well as his treatise called On Objects Carried Down by their Weight.

Ptolemy

Ptolemy

  This image is from a 15th century illuminated manuscript that depicts the astronomer Ptolemy looking at an astrolabe, a device used to show the positions of the Sun and stars at a given time and place.

  Ancient astronomy reached its zenith with the publication of Claudius Ptolemy's extraordinary work, Almagest (meaning the "greatest" in Arabic) in approximately 150 CE. A Greek Egyptian citizen of Rome, Ptolemy made his astronomical observations from the great cultural center of Alexandria in the years 127-151 CE. His 14-part text discussed mathematical and astronomical concepts, summarizing and refining contemporary knowledge, and applied geometric principles to show that the heavens moved in a logical and predictable pattern. It contains an expanded version of Hipparchus's star chart, and list of the 48 constellations that are the basis of today's constellation system.

  Although Ptolemy could not accept that Earth revolves around the Sun, he nonetheless accurately explained the uneven motion of the seven known planets by refining Eudoxus's theory that they were embedded and revolving concentric crystal spheres. Ptolemy pictured the heavens as a revolving sphere with a stationary rotating Earth at the center. His reasonings was erroneous, but his observations were so accurate that his geocentric view of the universe was accepted, with occasional minor refinements by Hindu and Arab astronomers, for more than 1,000 years.

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