Precession

As levels of the greenhouse gas carbon dioxide rise and warm the globe, Antarctica's ice will become more vulnerable to cycles on an astronomical scale, particularly the tilt of our planet is as it spins around its axis.

Spring starts in Earth's northern hemisphere

BELGRADE -- The spring equinox, the official start of the spring season in the northern hemisphere, this year falls on March 20.

At the same time, fall is beginning in Earth's southern hemisphere.