4.7: Solar radiation and Earth’s seasons

Seasons are caused by…

the tilt of the Earth on its axis (~23.5°)

Key dates in the Northern Hemisphere

• March and September equinoxes (~20 March and 23 September) 

  • All regions of Earth receive 12 hours of daylight and 12 hours of darkness

  • Start of spring and fall in the northern hemisphere

• June solstice (~June 21)

  • Northern hemisphere tilted towards sun for longest day

  • Summer begins

• December solstice (~December 21)

  • Northern hemisphere tilted away from sun for shortest day

  • Winter begins

Factors that affect solar energy

ASD

• The angle at which the Sun's rays strike varies.

• The amount of surface area over which the Sun's rays are distributed varies.

• Distance radiation travels through atmosphere

Insolation

Incoming Solar Radiation

• The portion of the Sun’s energy that is received by the Earth.

• Intensity of insolation

  • rate at which insolation is received (how strong it is)

• Angle of insolation

  • angle at which sun’s energy strikes earth (increasing angle increases the intensity)

greenhouse effect

Albedo

• percentage of reflection from surface (the ability of a surface to reflect light).

  • High albedo = lighter in color (ice, snow)

  • Low albedo = darker in color (soil, forest, fields)