The Dionysian

Can someone give me an explanation of this phenomenon? What is it? What causes it?

[ August 03, 2002: Message edited by: TPaine ]</p>

beausoleil

A google search under prEcession of the equinoxes should provide more information than you can shake a stick at.

Marduk

The earth rotates on it's axis (day/night) but it also has a slight swivel, if you stuck a pole through the Earth North to South the ends of the pole would also rotate in a small circle. But it is very slow, takes like 22,500 years to make a circle. This is where the astrotomical 'ages' come from, each age is about 2000 years, on the first day of spring the Sun will rise in the same constellation for that 'age'. Take a constellation like Orion, over a 22000 year period it will 'rise' and 'fall' sometimes higher in the sky, sometimes lower. That's how I remember it anyway.

Autonemesis

Precession is the motion of the direction of the Earth's rotational axis. If you spin a top, friction between the table and the tip on which the top is spinning, imparts a slight twisting force, causing the axis of the spinning top to begin to wobble in a circular motion. This is precession.

In the case of the Earth, tidal forces from the Sun impart the twisting force, and perterbations from the moon and the other planets also contribute. There is an additional motion called nutation, which is a "nodding" motion of the Earth's axis relative to the axis of precession. In other words, as the direction of the Earth's axis traces a great circle in the sky, it also nods up and down slightly, so the tilt of the Earth's axis relative to the axis of precession varies by a couple of degrees over a very long period.

Another way of describing nutation is to note that the Tropics of Cancer and Capricorn and the Arctic circles migrate north and south a couple of degrees over periods of hundreds of thousands of years. The solar analemma also undergoes changes in shape over the course of this cycle.

Have I given you enough search terms for Google yet?

[ August 03, 2002: Message edited by: Kind Bud ]</p>

The Dionysian

We are entering into the age of aquarius in 2012 are we not? Thanks for the information everybody.

[ August 03, 2002: Message edited by: TPaine ]</p>

Marduk

"We are entering into the age of aquarius in 2012 are we not? Thanks for the information everybody."

I don't think so, more like another 150 years, 2012 is when one of the major Mayan Calendars ends. or the day the aliens invade if you are an X Files fan.

Coragyps

Or nine years after The Rapture if you subscribe to some numerological musings we've seen on these boards recently.