Saturday, July 04, 2009

More on Cycles

I think I got "this post on the Aphelion of the earth's orbit" mostly right. It really does not make a lot of sense to locate the latitude of this event. I think the more interesting one would be the latitude of Perihelion because that is when we are closest to the sun. Because of the disconnect between the solstice and these events it would be really interesting is to see what schedule these events are on to line up. So I started looking around and found there are (at least) three movement two of which have a cycle:
  • The Orbital Eccentricity (a variation of the shape of the ellipse) and is a function of the gravitational attraction of all the other bodies in the solar system. When a body is at the extreme end of its ellipse it is said to be at Aphelion and when it is in its close end of its ellipse it is said to be a Perihelion. This value can be computed but I have not found a cycle associated with it.
  • The Axial Tilt (a variation in the tilt from the orbital plane of the axis of rotation of the planet). Presently this is around 23.4 degrees and is on a 41,000 year period and is getting smaller which means the earth is pointing more upright as time progresses.
  • The Precession of the Axis of rotation of the planet. (think how a gyroscope's axis describes a wobble as it spins). This is on a 25,800 year period. The north pole of the earth describes a circle of radius 23.5 degrees (equal to the axial tilt) around something called the ecliptic pole.