Sun-Earth System

Daily Motions of the Earth Precession is a gravity- induced, slow and continuous change in the orientation of a Earth’s rotational axis The Earth's rotation axis is not fixed in space. Like a rotating toy top, the direction of the rotation axis executes a slow precession with a period of 26,000 years

Annual Motions We see weather changes, day length changes, temperature changes as result of Earth’s motion around the Sun The plane in which Earth orbits the Sun is called the ecliptic

Effects of Earth’s Tilt Earth’s axis tilted to the ecliptic at 23.5 degrees As a result of the tilt of Earth’s axis and Earth’s motion around the Sun, the Sun changes its altitude in the sky The Earth’s tilt is most directly responsible for the seasons that we see every year

As Earth moves around Sun, the altitude of the Sun decreases in the northern hemisphere Summer solstice-Sun is at highest altitude in the sky (June 21); number of daylight hours at maximum Summer solstice-Sun is directly overhead at Tropic of Cancer (23.5N latitude) Winter solstice-Sun is at lowest altitude in the sky (Dec 21);number of daylight hours at minimum; Sun is directly overhead at Tropic of Capricorn (23.5S latitude) Solstices

Equinoxes Two positions Earth is not pointed at Sun; as result both hemispheres receive same amount of sunlight and Sun is directly overhead at the equator Called autumnal and vernal equinox (equinox means “equal nights”)