Solstices and Equinoxes
The solstice is an event in the Earth's orbit during which the tilt of the Earth's axis is pointed most directly towards or away from the Sun. The summer solstice for the northern hemisphere occurs within a few days of June 21 every year. It is on this day that the position of the Sun in the sky at noon is at its highest altitude of the year, and the position of the Sun at Sunrise and Sunset is farthest north for the year. The winter solstice is around December 21, marking the date on which the Sun is lowest in the sky at noon and rises and sets farthest south. The day of the summer solstice is the longest day of the year, and the day of the winter solstice is the shortest day of the year. The equinox is the time of year when the Sun appears in the sky at the intersection of the ecliptic and the celestial equator. Two such points exist: The vernal equinox (approx. March 21) marks the start of spring. The autumnal equinox (approx. Sept. 20) marks the start of autumn. At each of these points, the Sun rises due east and sets due west.