Today, we learn the time of the year. The
University of Houston's College of Engineering presents this series about the
machines that make our civilization run, and the people whose ingenuity created them.
I'm always forgetting the date. So I just pass my mouse
over the lower corner of the screen and it reminds me. I don't even have to turn
my head to look at the calendar! It's so easy that I have to kick myself to
realize how hard it once was to know just where we were in the course of a year.
So let us go back and meet the people of Chankillo. These were pre-Incans who,
2300 years ago, lived ten miles from the northwestern Peruvian coast. There,
against the western foothills of the Cordillera Negras, they'd built a large
This region holds many ancient ruins. But only recently did anthropologists from
Yale and the University of Leicester learn the meaning of another site, a kilometer
east of the temple. These ruins are divided by a low ridge. Along the spine of
the ridge are thirteen square towers between six and twenty feet high. They extend
over an eighth of a mile, and make the ridge look a little like the back of a
stegosaurus. All rather mysterious!
Now the scientists find observation posts on the flats to either side of the ridge.
They define an imaginary east-west line through the ridge. So hold that thought
while we come back to the problem of knowing the time of year.
It's easy enough to observe lengthening and shortening days. But when, in that cycle,
do we plant crops? How do we know just where we are in the year? If we can locate
sunset and sunrise on a horizon, then we can mark where the summer and winter solstice
occur, and we can fill in the middle. That's what went on here.
These pre-Incans built an artificial horizon along the ridge. Observers in the western
observation post looked eastward to trace sunrises; those in the eastern one looked west to trace
sunsets. The towers on either end marked winter and summer solstices. The rest of the
towers marked points in the passage of each half year.
These people probably broke time into blocks of a certain number of days. How many,
would depend on just how they used the towers and the gaps between them. It's really
very neat -- an annual sundial instead of the familiar daily sundial.
We know that the later Inca people practiced a highly developed worship of a sun god.
And here we surely see the roots of that worship.
At first, we might not realize just how early this was. History is compressed in the
Americas, because Paleolithic humans arrived here so late in time. That meant they had
to be late in inventing technologies like farming, writing, and calendar-keeping.
So: Here is the earliest known western calendar, and how clueless it makes me feel.
Each evening for 26 years, I've driven the same road home toward the setting sun.
Sometimes I think, "What a beautiful sunset!" Sometimes I just lower my visor and
squint. My car's dashboard tells me the date, and I've never noticed just where the
sun sets in December and where it sets in June.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
I. Ghezzi and C. Ruggles, Chankillo: A 2300-Year-Old Solar Observatory in Coastal Peru.
Science, Vol. 315, 2 March 2007, pp. 1239-1243. Or see these online summaries:
For some Andean prehistory, see:
(Images courtesy of Google Earth)
The Engines of Our Ingenuity is
Copyright © 1988-2006 by John H.