I'm a right that the difference is that precession indicates the direction of the inclination of the Earth'axis and the tilt is the quantity of this inclination? So that when there is no tilt there can't be any precession?

And are the inclination degrees of the precession and the tilt related or the same?

It seems that the precession causes different possible polarstar, but is the tilt also have effect on this?

Perhaps this above it not right, so what else is the difference? Is perhaps the precession just the changing of the tilt?


The Earth orbits the sun. The plane in which it orbits is called the Ecliptic plane, and perpendicular to the plane is a direction, known as the ecliptic pole. The direction of the Ecliptic pole is towards the constellation "Draco". The Earth's North pole doesn't point in the same direction. It points towards the pole star "Polaris" in Ursa Minor. The difference between these two poles is the axial tilt (it is about 23.5 degrees)

Over time the direction of the North Pole changes, it moves in a circle around the Ecliptic pole, taking about 26000 years to complete one circuit. This is precession. The amount of tilt doesn't change much since the North Pole moves in roughly a circle. The tilt varies over a few degrees with a period of about 41000 years. The variation in tilt is not precession.

So axial tilt and precession are not the same thing. One is the angle between the ecliptic pole and north pole, the other is the motion of the north pole relative to the ecliptic.

  • $\begingroup$ So the angle in degrees of the precession is always the same as the angle in degrees due to tilt? $\endgroup$ – Marijn Jan 30 '17 at 21:05
  • $\begingroup$ Please re-read. Precession is not an angle. It is the motion of the direction of the pole. "The angle in degrees of the precession" is meaningless $\endgroup$ – James K Jan 31 '17 at 20:55
  • $\begingroup$ Do you mean with that the tilt doesn't change much the difference of 21,5 to 24.5 degrees what I read somewhere? $\endgroup$ – Marijn Jan 31 '17 at 21:19
  • $\begingroup$ see edit. The variation in tilt is not precession. $\endgroup$ – James K Jan 31 '17 at 22:10

Tilt is the angle between the earth's rotation axis, and its orbital plane around the sun. Precession is the phenomenon whereby the direction of the tilt changes, which is why Polaris won't always be the pole star (until it comes round again). The amount of the tilt also varies, but only by a few degrees.


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