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History of Astronomy — Ancient Egypt

Ancient Egyptians. The ancient Egyptians had many practical uses for mathematics, such as building pyramids and other monuments, dividing land, calculating taxes, and most important, predicting the annual flood of the Nile River and calculating land boundaries after the flood waters subsided. They used a decimal counting system that even had fractions. The Greek philosopher Aristotle credited Egyptian priests with inventing mathematics, because that is where Greek mathematicians learned this science. The Rhind Papyrus contains much of Egypt's mathematical knowledge.

Egyptians created hieroglyphs, the most beautiful form of writing that the world has ever seen. There were often many ways of writing the same word. Scribes would choose the most visually pleasing combination of symbols. That, coupled with the forms of the characters themselves, truly made writing hieroglyphs an art. To these artist-scribes, a purely phonetic alphabet would have seemed crude. As a result, Egyptians used hieroglyphs for thousands of years. Recent inscription discoveries near the Valley of the Kings by Professor John Darnell of Yale University have shown that Semitic people living in Egypt, probably mercenary soldiers and laborers who did not have years of training to master hieroglyphs, developed the first phonetic alphabet in conjunction with Egyptian scribes around 2000 B.C.E. — at least 200 years before the Poenecians, who had been given credit for inventing the earliest phonetic alphabet.

Osiris (shown at far left) was the Egyptian mythological First Pharaoh. The Egyptians wrote his phonetical hieroghyphic name (shown at near left) as "Osir." The hieroglyphic symbols, which are the first three symbols at the top left corner of the far left drawing, read as follows: the black seat represents 'os'; the eye represents 'ir'; the seated figure is the determinative symbol to indicate that this word is the name or a title of a god. The signs 'os' and 'ir' are written in reverse order in this case because the seat and seated figure are both vertical objects, and look more aesthetically pleasing if written together, with the horizontal eye above. The names of gods or pharaos (who were considered gods) are often written first in a hieroglyphic sentence, regardless of the grammatical position of their name within the sentence. That way no other characters in the sentence would have their backs turned towards the deity.

According to ancient Egyptian mythology, after death Osiris became the constellation now called Orion (shown at middle left in a Hubble Space Telescope photo). Astronomers later found many connections between the Orion constellation and the way ancient Egyptians built the Pyramids. For example, Orion's "belt" of three stars in the middle matches the arrangement of the three Pyramids on the Giza Strip (including the Great Pyramid), with the third pyramid a little smaller and above the line formed by the other two pyramids.

In ancient Egypt, the rising of the star Sothis (Sirius, the "Dog Star") with the Sun in the summer foretold the annual flooding of the Nile River at the capital, Memphis. Egyptians found that the stars were more accurate over thousands of years than their solar calendar of 365 days. Because the Egyptian calendar did not have leap years, their year cycled through the seasons completely every 365 times 4, or 1460 years. This was known as a "Cycle of Sothis" because Sothis (Sirius) would rise with the Sun on the same day every 1460 years. Actually because of precession of the equinoxes and proper motion of Sirius the period was slightly less, but Egyptians found this cycle of 1460 years.

Although the Egyptians knew of this quarter-day error, they maintained their 365-day calendar for ceremonial reasons. Their year was divided into twelve 30-day months, followed by a five day feast period that was not considered lucky for any work. Over ancient Egypt's history of at least three thousand years, the months completely rotated through the seasons at least twice.

The Egyptians also divided the stars into 36 "decans" (each spanned 10° of a 360° circle). Each decan had its group of associated stars. These stars are represented in tombs and elsewhere. However, Egyptians did not seem to develop advanced theories about the motions of the planets. Their entire survival was centered around the annual flooding of the Nile, and the planets' motions did not affect this flooding.

Because of precession of the equinoxes, Sirius now rises later than the traditional flooding of the Nile in Memphis, which was June 25 before the Nile was dammed. But from 3,000 B.C.E. to 1,000 B.C.E., the rising of Sirius at sunrise came close enough to the annual flooding at the ancient capital of Memphis.