| A | B |
|---|
| insolation | energy the Earth receives from the sun; incoming solar radiation |
| seasons | the annual cycle of weather conditions as the Earth orbits the sun |
| duration of insolation | hours of daylight |
| angle of insolation | the angle of the sun above the horizon |
| azimuth | the angle measured from north to an object; the compass direction |
| rotation | the spinning of an object around an internal axis; on the Earth it causes day and night |
| direct (vertical) rays | sunlight that strikes the Earth from directly overhead (the zenith) |
| equinox | the time when the sun's vertical rays fall on the equator; all locations have 12 hours of daylight |
| solstice | time when the vertical rays of the sun fall on a tropic (Cancer or Capricorn) |
| radiative balance | an equilibrium between energy coming into the Earth (insolation) and energy given off by the Earth (terrestrial radiation) |
| zenith | point in the sky directly overhead |
| revolution | the orbital motion of a satellite around its primary; the Earth revolves around the Sun |
