HomeSolar SystemStarsOther WorldsCosmos' LifeExplorationExtras
-Pre-20th Century-20th Century-21st Century So Far-Near Future-


Babylonians | Greeks | Egyptians | Others | Calendars

Pre-20th Navigation


Egyptians had an entire mythology built around astronomy, but so did nearly every other ancient civilization. What is most remarkable about Egyptians ties into one of the Wonders of the Ancient World -- The Pyramids. The amazing accuracy to which the pyramids are aligned have sparked movies, alien conspiracy theories, and many different astronomical theories as to how they were made.

Besides the pyramids, this page discusses the planets, constellations, and mythologies around these celestial objects.


Egyptians used astronomy to help build some of the most impressive architecture on Earth: The Pyramids. By using knowledge of the sun and constellations, Egyptians were able to align the pyramids and shafts within the pyramids with the cardinal directions, as well as with star groupings that held spiritual significance.

Due to the high accuracy with which the Egyptians constructed the pyramids, Kate Spence's (an Egyptologist at the University of Cambridge) work in 2000 has allowed the date of construction of the Great Pyramid at Giza to be pinned to an accuracy of ±5 years (inconsistencies of dynastic records and radiocarbon dating allowed an accuracy of only ±100 years). Previous studies had found it to be constructed around 2550 B.C.

The Great Pyramid, also called the Pyramid of Khufu (or, in older texts, as Cheops), has sides which deviate from true North by an average of less than 3 arcmin. They are also nearly perfectly straight, varying no more than 2 cm (2/3 in.) in their 230 m (755 ft) length. This accuracy is the most precise of all the subsequent pyramids, which actually grew more inaccurate the latter they were made. Spence assumed that pyramid construction began in the second year of a monarch's reign.

Between the reigns of Snofru and Neferirkare (~2600-2400 B.C.), eight major pyramids were constructed, all in a nearly straight line. Researchers which propose stellar alignment methods (stellar meaning stars, not stellar meaning really good) agree that the Egyptians used northern or circumpolar stars for orientation of the east and/or west sides of the pyramid. Most studies show that it was mainly the west side that was accurately aligned (because it is the best aligned), while the other sides were determined through the creation of right angles.

The accuracy - or lessening of accuracy - trend suggests that stellar methods were used in contrast with solar. A solar method would not yield the accurate results found in the earlier pyramids. The stellar orientation scheme, however, would be supported by the progressive deviation of the alignments from true North, which could not be achieved using a solar orientation method. The increasing inaccuracy is probably a result of precession - something the Greeks discovered two millennia later.

It is precession that Spence used to date the construction of the Great Pyramid. The Earth precesses once every 25,785 years (≈50.262 arcsec per year of motion). Because it takes so long for this motion to occur, it is not noticeable unless one has extremely accurate position measurements or has observations spanning thousands of years, neither of which were available to the ancient Egyptians.

The "North Star" of the period was α-Draconis, also known as Thuban, though it was 2° away from true North at the time of Khufu. However, rather than the use of one star, Spence proposes that two circumpolar stars were used, and that an imaginary chord was drawn between the two as they rotated about celestial North. When the two stars are vertically aligned, an alignment with the stars of a plumb-line will be exactly oriented to true North. Then, because of precession, this method will become increasingly inaccurate with time.

Through back-tracking precession rates, and examining the sky between 2750-2350 B.C., Spence looked for pairs of bright stars within 15° of the north celestial pole. She found only two pairs of stars, the pair ζ-Ursae Majoris and β-Ursa Minoris and the pair ε-Ursae Majoris and γ-Urasae Minoris, that fit this time period (the former was 2467 B.C. and the latter was 2443 B.C.). Based upon these, Spence concludes that the date of 2478 B.C. for the alignment of the Great Pyramid.

Sky Maps

The Egyptians, like any other culture, watched the sky and mapped it. As early as 2150 B.C., they had identified 36 groups of stars which they called decans. They used these stars to tell time at night, for they chose the stars so that they would rise 40 minutes later each night.

Based upon their observations, by 1100 B.C. they had divided the sky into five very large constellations. The constellations were generally animals, such as the Hippopotamus, Bull, and Crocodile. Later generations divided these further into approximately 25 constellations.

Astronomical Ceiling of Senmut

The earliest known astronomical ceiling is that in the tomb of Senmut, the architect and favorite of Queen Hatshepsut (~1473 B.C.). A decan list is present, showing unmistakably that a star clock was copied. The last decan is Sirius-Sothis and have positions such that the star clock copied on the ceiling must be dated to the last revision in the Twelfth Dynasty, 400 years earlier.

Besides the decan list, there are stars and deities present. The constellations of the ship, sheep, Osiris (Orion) and Isis are also present. To the left of the decans, where a star clock would continue with the triangle decans for epagomenal days, Senmut has a mixture of decans and planets. Jupiter and Saturn are before the triangle decans as two falcon-headed figures, and Mercury and Venus follow the decans where Mercury is represented as Seth and Venus as a heron.

The Ceiling of Senmut is also the first place in which all the known planets (Mercury, Venus, Mars, Jupiter, and Saturn) except Mars appear. Mars appears with the others in the astronomical ceiling of Ramesseum 200 years later. Jupiter, Mars, and Saturn were usually separated from the other two, Venus and Mercury, and were tied to the sky god Horus.

The Sky Mythology

The sky was represented by Nut, who was a female goddess. Osiris, the form of the Nile River, was Nut's opposite. Osiris was first and foremost the ruler of the Dead. Life came through resurrection. He was also the sun, the moon, and the stars of the present-day constellation Orion. He is basically the god of everything.

The main myth surrounding Osiris is that he was fathered by Geb, the Earth, and born of Nut. He became the king, organizer, and the spirit of Egypt. His sister and consort was Isis, represented in the sky by Sirius (the brightest star). Osiris' brother and eventual murderer was Set, who was associated with the Big Dipper.

Other figures of the sky was Ra (also translated as Re), who was the sun god. Maat sailed the sky with Ra and was his female companion; she was considered the gift of light and righteousness. The moon was also attributed to Khonsu, the runner, and Thoth, the scribe or keeper of records.

The planets also had astronomical significance: Jupiter, Mars, and Saturn were all associated with Horus, the falcon-headed god of the sky. More specifically, Jupiter was "Horus-who-bounds-the-two-lands," or "Horus-who-lluminates-the-two-lands." Saturn was "Horus-bull-of-the-sky" or "Horus-the-bull," while Mars was "Horus-of-the-horizon" or "Horus-the-red."

Venus, also called the "crosser" which was probably a reference to its presence in both the morning and evening. Other than this name, there is no actual textual evidence to prove that it was recognized as the same object in both the morning and evening, but this is generally believed to be true. More often it was represented by Bennu, a heron-like bird associated with the phoenix myth, which related it back to Osiris.

Mercury had the simplest name of the planets, Sbg, though its meaning is unknown. It was frequently associated with Seth, the enemy of Horus and murderer of Osiris. A text which dates to the era of Ramses VI (1148-1138 B.C.), refers to Mercury as "Seth in the evening twilight, a god in the morning twilight," conclusively showing that it was recognized as the same object in both the morning and evening.

color bar
© 1997-2006, all rights reserved