Astronomer traces Zodiac's time and place of birth

Calculating its horoscope any minute now

By Lucy Sherriff • Get more from this author

Posted in Space, 4th June 2007 12:40 GMT

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An astronomer has traced the origins of the earliest known descriptions of what would become the constellations of today's Zodiac to the region which once held the Assyrian cities of Ninova and Asur.

The descriptions, which include more than 200 astronomical observations, are written in cuneiform on a collection of clay tablets, known as MUL.APIN. The tablets are known to have been made in Babylon in around 687 BC, but archaeologists believe they are only transcriptions of much earlier records.

Now Brad Schaefer, an astronomer at Louisiana State University in Baton Rouge, thinks he knows just how much older the information on the tablets is. Using modern astronomical techniques, he has dated the observations to 1,370 BC, give or take 100 years. He also says the observations were made within 100km of 35.1° N.

The tablets record the day of the year that certain groups of stars, constellations, appear in the sky at dawn. These constellations are widely thought to be the precursors of the modern Signs of the Zodiac.

These dates change over time thanks to precession, a slight wobble in the Earth's axis, and in combination with other information, such as when the constellations appeared directly overhead, can be used to pinpoint the time the information was recorded.

Schaefer double checked his technique by calculating when and where he was, using the same astronomical measurements. Nature.com reports that he was able to calculate the date and place more precisely with his own observations, although he is not sure why this is so.

We'll refrain from any jokes about diaries and maps, on the basis that this would detract from a very cool piece of historical detective work.

Nature.com has a picture of the tablets here. ®

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