Precession

 Image: R. Stockli, NASA


Scientific headlines in the last few years have centered much on orbital forcing in the quest of finding the reasons for a rapid global warming. The oscillations of the ice ages are thought to be caused primarily by orbital rhythms recognized in their entirety in the beginning of the last century. Termed the Milankovitch cycles, these rhythms are precession (latitudinal variation), obliquity (tilt of Earth's axis), and eccentricity (distance to the Sun). Of the three, precession, has the shortest periods and may therefore be responsible to some degree for the observable changes of the atmosphere today. Precession means advancement refering simply to the earlier arrival of the seasons as years goes by. The signs of precession were noticed already by the astronomers of the antique world, possibly as early as the Sumerians. The phenomenon causes the celestial hemispheres to rotate so that the positions of the stars change in regard to the Sun. This was an important parameter for early navigation, time keeping, and cultural beliefs. Even today it holds appeals as we celebrate i.e. in the musical Hair the dawning of the age of the aquarius and watch the sky with growing interest and the help of highly sophisticated technology. Minor forms of precession called nutation were discovered in the last century and have raised concerns about the stability of Earth's motion and its magnetic field under changing atmospheric and oceanic circulation patterns. Click on the button below to find out more