The Earth’s 23.5° tilt with respect to the ecliptic affects both the angle of solar radiation and the length of daylight hours over any given region of the Earth. The continuous changes in these two factors during the Earth’s yearly revolution around the Sun are responsible for the seasons.

Solstices refer to the two times each year when solar radiation, at noon, reaches its northernmost (23.5°N) and southernmost (23.5°S) point on the Earth’s surface. These dates are on or around June 21 and December 21. Equinoxes refer to the two times each year when solar radiation, at noon, is directly over the equator. These dates are around March 21 and September 22.

Summer

Kinetic energy refers to energy associated with an object by virtue of its motion, whereas potential energy refers to an object’s capacity to do work. In other words, one refers to the process of working, the other merely refers to the potential to work.

Conduction is the transfer of heat through electron and molecular collisions from one molecule to another. Convection is heat transfer that involves the actual movement or circulation of a substance. Advection is the horizontal flow of air known as wind. Radiation is the transfer of energy through electromagnetic waves moving at the speed of light and is the only form that can travel through the vacuum of space.

• First law: All objects continually emit radiant energy over a range of wavelengths.

• Second law: Hotter objects radiate more total energy per unit area than do colder objects. 

• Third law: Hotter objects radiate energy in the form of shorter wavelength radiation than do cooler objects.

• Fourth law: Objects that are good absorbers of radiation are also good emitters.

Absorption of radiation refers to the amount of energy absorbed by an object and depends upon the wavelength of radiation and the object’s absorptivity. Transmission, however, is the process whereby radiation passes through the atmosphere without interacting with the gases or other particles in the atmosphere. 

Scattering is a general process in which radiation is forced to deviate from a straight trajectory and instead may head out in any direction. Reflection is the process whereby light bounces back from an object at the same angle and intensity at which it was received.

Diffused light is light which has been scattered by atmospheric particles and is responsible for lighting areas that are not in direct sunlight.

Clouds appear white due to their high reflectivity.

Albedo is the fraction of radiation that is reflected by an object.

The majority of solar radiation has wavelengths shorter than 2.5 micrometers, whereas the majority of terrestrial radiation is emitted in wavelengths between 2.5 and 30 micrometers.

Although the atmosphere is an effective absorber of radiation emitted by Earth’s surface, it is nevertheless quite transparent to the band of radiation between 8 and 12 micrometers. This range is referred to as an atmospheric window, because it acts much as clear window glass does to visible light, allowing radiation in this wavelength to escape back into space.

Natural

The Earth’s surface gains energy by absorbing both incoming solar radiation and longwave radiation emitted by the atmosphere. It loses energy through the processes of conduction and convection working together, through evaporation of surface water, and through emission of longwave radiation to the atmosphere and space.

The Earth’s atmosphere gains energy by absorbing heat through conduction and convection from the surface, through condensing water vapor from the surface, by absorbing terrestrial radiation and, aided by clouds, by directly absorbing some solar radiation. It loses energy, again aided by clouds, through reflection of solar radiation back into space, through radiating heat energy back to the Earth’s surface and through radiating heat energy into space.