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Incan Lore Rings True
Thu Jun 09, 2005
Listen in RealAudio 
In the central Andes of South America, a single harvest can make the difference
between feast and famine. Farmers from the ancient days of the Incan empire, to now,
have "read" the sky to figure out the best time to plant their crops. Recently, this ancient
custom has been validated by science. Hi I'm Bryan Yeaton and this is The Weather
Notebook.
It's during this time of year that winter begins in South America. Each night during the
middle of June, mountain villages across Peru and Bolivia closely watch the northeast
sky for the Pleiades constellation. The Incans worshiped this cluster of stars. If the
Pleiades were dimmer than usual, that was a bad sign. They learned that there would
be less rain than usual for the growing season to come. If the stars shone brightly, that
meant abundant rain.
Why would the stars go dim before a drought? It turns out that high, thin cirrus clouds
often sweep across the Andes in the summer before an El Niņo kicks in. These clouds
may be too thin to see with the naked eye, but they're enough to cause a noticeable
dimming of the stars at night. The villagers of long ago correctly figured out that cirrus
was a sign of the drought that El Niņo would later bring to their land, even though they
didn't know anything about El Niņo itself.
Villagers across the Andes still watch the stars in June. If the stars are dim, they'll
delay their potato planting a few weeks so that the dry spring is less likely to damage
their crop.
The Weather Notebook is a production of the Mount Washington Observatory, with
support from the National Science Foundation.
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