Earth, sun and moon

Intensity is decreased as angle changes Intensity = max Intensity is decreased as angle changes Angle = 90 Angle = 0 Intensity = 0

Direction of rotation North Pole Sun’s rays Axis DAY NIGHT

A year is the time for the Earth to orbit the Sun. 1 Earth year = 365.25 days Sept SUN June Dec Direction of orbit A year is the time for the Earth to orbit the Sun. March

The sun’s rays are pretty close to parallel when they reach the surface of the Earth. Earth’s axis Equator If the Earth’s axis was always perpendicular to the Sun’s rays then direct sunlight would always shine on the equator and we would have no seasons. S

However, the Earth actually exists so where its angle of rotation is at an angle of 23.5O to its plane of orbit N Angle of incidence = 23.5O Earth’s axis Plane of orbit Equator S

The Earth maintains this angle throughout its entire orbit.

Source: http://daphne. palomar. edu/jthorngren/tutorial Source: http://daphne.palomar.edu/jthorngren/tutorial.htm, accessed 15th August, 2007

Source: http://daphne. palomar. edu/jthorngren/tutorial Source: http://daphne.palomar.edu/jthorngren/tutorial.htm, accessed 15th August, 2007

Animation of Phases of Moon Source: http://www.wpclipart.com/space/illustrations/Moon_Phases.png, accessed 16th August, 2007 Animation of Phases of Moon