Two of the best-known and most-watched constellations by prehistoric Southwestern agriculturists were the Pleiades and the Big Dipper. By observing stars above the North Star at twilight, ancients knew the time of year within a few days and thus could assess their temporal location within the yearly cycle at a glance.[more]
Another way to track the yearly cycle is to watch the sun move along the horizon, day to day, at either sunup or sunset. Daily observations need to be made at the same location every time. This is a good calendar method for a village, for stationary people. If planting begins when the sun reaches a certain cleft in the horizon, you'd need to know which horizon is specified. In short, a given horizon calendar is good for only one spot on Earth.
The twilight calendar is ideal for people who are semi-nomadic, those lacking a stationary horizon. The twilight calendar is available and accurate for every location, every spot in the Northern Hemisphere and reads the same around the globe. Nautical twilight begins with the appearance of fourth-magnitude stars. When the stars represented by red dots in the handle of the Little Dipper appear, it is time to read the twilight calendar. This occurs roughly an hour after sunset.
To use the twilight calendar, observe the North Star at twilight and take note of the stars/constellations directly above it. For example, when the leading two stars of the Big Dipper are above the North Star at twilight it is time to begin planting corn/beans. When the middle star in the Dipper's handle is above at twilight, it is time to stop all planting.
As you become more familiar with the northern sky at twilight it is a simple matter to assign important dates of any culture to the twilight calendar. A wealth of stars was left out of the diagram so the concept could be clearly presented. New Year's Eve, the Fourth of July? Piece of cake. Just find a star that signifies your birthday, anniversary, or any other meaningful date. When that star reappears again in the same location you will know the exact time of year.
The Diné (Navajo) planting season coincides with the absence of the Pleiades from the night sky (May 8 to June 8—the green sector). The Diné plant after Pleiades has set with the sun and before it returns and is visible in the early morning sky. "Plant while Pleiades can't see". As a general rule-of-thumb, planting while the Big Dipper is above the North Star has worked well on the Colorado Plateau in the Four Corners region of the United States for the past thousand years.
Late in October, the Pleiades begins to rise at twilight. The period until the Pleiades is at its zenith at twilight (February 8) is the ceremonial season (red sector). At Taos Pueblo a “quiet period” is enforced as the Big Dipper (green sector) passes beneath the North Star.
The yellow horizontal line signifies the horizon and can be adjusted from 0 to 41 degrees north latitude. The size of the dots representing stars is an indicator of their brightness and the chart centers on the North Star, Polaris. Constellations denoted are Ursa Major, Ursa Minor, Cassiopeia, Cepheus, and part of Draco. In the Northern Hemisphere, the North Star neither sets nor rises. It is there, in the same place in the sky, night and day.[less]
Wolfram Demonstrations Project
Published: March 7 2011