A solstice is an event in which a planet's poles are most extremely inclined toward or away from the star it orbits. Here, the Southern Hemisphere gets the maximum INTENSITY of the Sun's rays during the December solstice.
An equinox occurs when the position of the sun is exactly over the EQUATOR. When this happens, the hours of daylight and the hours of darkness are about equal almost everywhere on Earth. EQUINOXES take place twice a YEAR. Autumn, or fall, begins with the autumnal equinox.