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Professor Anthony Aveni

Question for July 2009

Did the Aztecs know of different star constellations to the ones we see today? Asked by Stroud School. Chosen and answered by Professor Anthony Aveni.

Pic 1: Aztec astronomer at work; Codex Mendoza, folio 63r (detail)
Pic 1: Aztec astronomer at work; Codex Mendoza, folio 63r (detail) (Click on image to enlarge)

The Aztecs recognised the Pleiades. They called it the Fire Drill, which was used to create new fire every 52 years. They had a Scorpion, which may have been comprised of the same stars as our own, a Ballcourt, equivalent to our Gemini, and a few others are pictured that we are still trying to identify... and no doubt many more.

Pic 2: An artist’s impression of how Aztec architects may have set up an alignment with the rising Pleiades
Pic 2: An artist’s impression of how Aztec architects may have set up an alignment with the rising Pleiades (Click on image to enlarge)

The Aztecs of Tenochtitlan, who visited nearby Teotihuacan during the time of Europe’s Middle Ages, said that it was the birthplace of the gods. More than 2,000 years ago, the builders of Teotihuacan surveyed and laid out one of America’s first great cities. It would come to house more than 100,000 people. Along the Street of the Dead, in the stucco floor of a building located just south of the Pyramid of the Sun, lies a clue that serves as visible evidence of the precise course taken by Teotihuacan’s architectural planners - a petroglyph [rock engraving] pecked into the stucco in the shape of a double circle centered on a cross (see Picture 3). The design closely matches another carved on a rock outcrop 3 km to the west of the Sun Pyramid.

Pic 3: Illustration of a pecked cross petroglyph, found at Teotihuacan
Pic 3: Illustration of a pecked cross petroglyph, found at Teotihuacan (Click on image to enlarge)

In the 1960s archaeologists discovered that a line between this pair of architect’s benchmarks lies almost exactly parallel to the east-west street of the ancient capital. A third petroglyph on Cerro Gordo, a mountain to the north overlooking the city, along with a fourth on the south, may have marked out significant geographic directions. Picture 2 shows how simple paired cross-stick tools might have been used to orient the city.
If you stood over the petroglyph near the Street of the Dead 2,000 years ago, and cast your eye out along the east-west axis of Teotihuacan towards the marker on the western horizon at the correct time of year, you would have seen the Pleiades setting over the mountain horizon. Why align a city with the Pleiades?
First, they passed directly overhead in the latitude of Teotihuacan at the time the city was erected, thus signalling the important fifth cardinal direction. And second, the Pleiades’ reappearance in the east, after having been lost in the light of the glaring sun for 40 days, happened on the very day the sun also passed the zenith.

Pic 4: Images of ancient Mexican firedrills (left: stamp design, right: from the Codex Laud)
Pic 4: Images of ancient Mexican firedrills (left: stamp design, right: from the Codex Laud) (Click on image to enlarge)

Here was a visible, convenient timing mechanism to signal the start of the new year...
Aztec reverence for the great city of Teotihuacan, home of the gods and the place where time was born, is as justified as our gratitude to Rome and Athens for the gifts that emanate from our own Western Classical tradition.

Pic 5: Teotihuacan, view from the north, looking along the Street of the Dead
Pic 5: Teotihuacan, view from the north, looking along the Street of the Dead (Click on image to enlarge)

Extra material adapted from Professor Aveni’s book ‘People and the Sky’, 2008

One of a series of recent children’s questions on astronomy, all kindly answered in brief by Professor Aveni. The others are:-

Q. Did the Aztecs think the earth was round or flat? A. The Aztecs were not interested in the shape of the earth because they didn’t descend from the Greeks. Different cultures have different issues & that wasn’t one of them.

Q. Is it true the Aztecs learned the cycle of Venus from the Maya? A. We now know that the references to Venus in calendars from Central Mexico look the same as those of the Maya. It’s likely that’s where they came from, but we have no proof.

Q. How did Aztec people tell the time? A. The basic “unit of currency” was the day. They didn’t break the day into hours, minutes, etc. There was a “town crier” in Tenochtitlan who drummed out the time when an important civic event was scheduled to occur.

Q. Do we know when the cycles of the sun, the moon and Venus will next come together? A. Venus and the sun realign every 8 years. Throw in the moon and it’s 99 years.

Q. Did they have a highest number (in their calendars/counting systems)? A. There are no really big numbers in Aztec documents. Chroniclers after the conquest say the Aztec creation periods were measured in millions of years but we can’t be sure.

Q. Why were they so into Astronomy? A. If you want to anchor human and natural events together no part of the environment is more reliable than the sky. First rains may come late, flowers may blossom early, and the time a hibernating animal emerges from sleep may vary, but sky events happen with extraordinarily precise regularity. Try looking up and you’ll find out.

Q. Were the Aztec day signs related to our star signs? A. There were 20 day names — after plants, animals, forces of nature; e.g. flower, jaguar, earthquake. Ours are named after Nordic versions of the old Greek Gods.

Q. How many planets did the Aztecs believe existed? A. We can be sure that the Aztecs recognized the motion of Venus. I think they surely were aware of Mercury, Mars, Jupiter and Saturn because all are bright and move noticeably among the stars, but we have no documents that prove the case.

Picture sources:-
• Picture 1: scanned from our copy of the 1938 Cooper Clark facsimile edition of the Codex Mendoza (original in the Bodleian LIbrary, Oxford)
• Picture 2: illustration courtesy of Professor Anthony Aveni
• Picture 3: scanned from Anthony Aveni’s book People and the Sky: Our Ancestors and the Cosmos, Thames & Hudson, 2008, p. 131
• Picture 4: images scanned from our own copies of a Mexican postage stamp and of the ADEVA facsimile edition of the Codex Laud (original in the Bodleian LIbrary, Oxford)
• Picture 5: photo from Wikipedia

Professor Anthony Aveni has answered 7 questions altogether:

Is it true the Aztecs learned the cycle of Venus from the Maya?

Did the Aztecs think the earth was round or flat?

How many planets did the Aztecs believe existed?

How did Aztec people tell the time?

Did the Aztecs know of different star constellations to the ones we see today?

What sort of gadgets did the Aztecs have?

Why did houses have no windows?

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