Whats the reason for precession?
The law of conservation of angular momentum requires that a spinning object stays spinning in the absence of rotating forces (“torques”): a force like gravity makes the direction of the spin axis move in a precessing circle, but can’t make the gyroscope wheel fall over. Similarly, the force of gravity from the Sun and Moon trying to align the Earth’s axis perpendicular to the ecliptic plane makes the Earth’s axis of rotation precess. Here’s a link with a bit more detail about gyroscopes for those interested: http://www.howstuffworks.com/gyroscope.htm. We’ll likely revisit angular momentum a bit in some other contexts later in the course.
