12 January 2005

Astronomical dating of an historical artifact

This Science News article is reporting on how an historian is linking the carvings on an ancient Roman sculpture to the work of the Greek astronomer Hipparchus.

The Farnese Atlas (shown below) displays Atlas holding the heavens as depicted by constellations carved on a sphere.

Farnese Atlas

Bradley Schaefer of Louisiana State University (the wife's alma mater) studied the location of the constellations on the sculpture and used the phenomenon of precession [Wikipedia] to calculate the date of the Earth when the stars would have been in those locations. Precession in this context is the amount that the Earth's axis moves to alter our view of the stars over time. Imagine the Earth's axis as a stick with its end moving in very tiny circles. Each change in position on those circles changes our view of the stars, and it takes 25,800 years for the axis to move completely around the circle.


So, by taking the current position of the constellations and calculating backwards in time, Schaefer matched the constellations on the Farnese Atlas to 125 BCE plus-or-minus 55 years. To have an accurate representation of the constellations, the sculptor would need a star catalog [Wikipedia] (which is what it sounds like, only more ambitious a task in the ancient world). The star catalog in question only exists today through historical references, and its authorship is in question. However: (1) by the sculptor accurately representing the constellations and (2) by Schaefer dating the precessionally-adjusted constellations to 125 BCE, he discovered that it must have been created by Hipparchus. From the news article:

Other theories about who wrote the star catalog include observers who were either too early -- including a poet writing around 275 BC and an Assyrian observer around 1130 BC -- or too late. This includes the astronomer Ptolemy, writing in 128 AD.

The Wikipedia article on precession points out that it was discovered by the Greek astronomer Hipparchus [Wikipedia] in 130 BCE. So, coincidentally, his discovery of precession helped point us to him as the author of a lost star catalog.

[ posted by sstrader on 12 January 2005 at 11:38:10 AM in Science & Technology ]