Ancient astronomers were highly sophisticated observers of the night sky. Though they lacked telescopes or any kind of magnification device, stargazing is one of the only things you could do at night, particularly if your spouse was tired and the kitchen slave let the fire die. Five of the eight planets — Mercury, Venus, Mars, Jupiter, and Saturn — were well-known to ancient astronomers.
Now, a new discovery suggests that the ancient Babylonians didn’t just track the planets — they used geometric methods that foreshadowed the development of calculus to accurately model how far Jupiter traveled over a 60-day period. Up until now, Europeans in the late-Medieval period (1300s) were thought to be the first astronomers to use this type of model.
The time-velocity graph described in the cuneiform tablets accurately models how Jupiter’s displacement changes over time. The planet’s motion appears to slow from Earth before finally pausing and reversing course.
While we knew ancient Babylonians had a thorough understanding of geometry, this is the first time we’ve seen it applied to astronomy. Mathieu Ossendrijver, of Humboldt University, put the pieces of the ancient puzzle together by combining the information on four tablets housed in the British Museum with a photo of a tablet fragment given him by an Assyriologist. This fifth tablet fragment was tiny, at roughly two inches by two inches, but it proved critical to deciphering the puzzle.
By comparing the information on the fifth tablet against the data on the other four, Ossendrijver discovered that the five tablets described a method of calculating the distance Jupiter had traveled over time. Most ancient astronomers had exhaustive charts and tables that described the position of planets relative to one another based on the time of year. The idea of describing a planet’s motion over time as a geometric shape, in which the space under the curve equals the distance traveled, was unheard of at the time.
Little is known about why the Babylonians developed geometric astronomy, and the tablets contain no data on their motivations. One thing we do know is that the planet Jupiter was associated with Marduk, the head of the Babylonian pantheon of gods. It’s possible that the calculations were related to a ceremony or religious rite. But it’s impossible to know what motivated these ancient astronomers to make an enormous intellectual leap from describing the motions of planets relative to each other to deriving the distances they traveled over time by using geometry.
January 29, 2016