Section 6: Solar Energy & Seasons

GES 108

Solar Energy

Energy emitted from the Sun in the form of electromagnetic radiation. It is the primary energy source driving Earth’s climate, weather, and life systems. Solar energy is renewable, carbon-free, and essential for processes like photosynthesis and the water cycle.

Temperature

A measure of the average kinetic energy or motion of molecules within a substance. Faster molecular motion means higher temperature.

Celsius

A temperature scale based on the freezing (0°C) and boiling (100°C) points of water at standard atmospheric pressure.

Fahrenheit

A temperature scale commonly used in the United States, where water freezes at 32°F and boils at 212°F.

Kelvin

The absolute temperature scale used in scientific measurements. Zero Kelvin (0 K) represents absolute zero, the point at which molecular motion theoretically stops.

Heat

The transfer or movement of energy from one body or area to another due to temperature differences.

Conduction

The transfer of heat energy through direct contact between molecules or objects. Example

Convection

The transfer of heat through the movement of a fluid, such as air or water, where warmer portions rise and cooler portions sink.

Advection

The horizontal movement of heat or other atmospheric properties by wind, such as when warm, moist air moves over a cooler surface to form fog.

Radiation

The transfer of energy through electromagnetic waves, allowing heat to move through the vacuum of space from the Sun to Earth.

Radiant Energy

Electromagnetic energy that travels as waves, including visible light and heat.

Ultraviolet Radiation (UV)

A type of solar radiation with short wavelengths that can cause sunburn and cellular damage. Divided into UVA, UVB, and UVC types.

Visible Light

The portion of the electromagnetic spectrum that human eyes can detect. It makes up a small fraction of solar radiation.

Infrared Radiation

A form of electromagnetic radiation with longer wavelengths than visible light, primarily responsible for the heat we feel from sunlight.

Near Infrared

Infrared radiation with wavelengths just beyond the visible spectrum, which we cannot see or feel. Example

Thermal Infrared

Infrared radiation with slightly longer wavelengths than near-infrared, which we can feel as heat. Example

Photon

A particle or packet of radiant energy that travels in waves. Hotter objects emit more photons with shorter wavelengths.

Electromagnetic Spectrum

The complete range of all electromagnetic radiation, from gamma rays (short wavelengths) to radio waves (long wavelengths).

Wavelength

The distance between two corresponding points of a wave. Shorter wavelengths correspond to higher energy and temperature.

Shortwave Radiation

Radiation with wavelengths less than 4 micrometers, emitted primarily by the Sun.

Longwave Radiation

Radiation with wavelengths greater than 4 micrometers, emitted primarily by Earth as thermal infrared energy.

Insolation

Incoming solar radiation that reaches Earth’s surface. It can be transmitted, reflected, scattered, or absorbed by Earth’s surface and atmosphere.

Transmission (of Solar Energy)

The passage of solar energy through the atmosphere to Earth’s surface without being absorbed.

Reflection (of Solar Energy)

The return of solar energy back into space without being absorbed. About one-third of incoming solar radiation is reflected.

Scattering (of Solar Energy)

The random redirection of solar energy in many directions by particles or gases in the atmosphere, creating diffuse light.

Absorption (of Solar Energy)

The process by which solar energy is taken in by Earth’s surface or atmosphere and converted into thermal infrared heat.

Albedo

The measure of a surface’s reflectivity — the fraction of incoming solar radiation that is reflected rather than absorbed. Darker surfaces have lower albedo (absorb more heat), while lighter surfaces have higher albedo (reflect more heat). For example, black pavement heats quickly due to low albedo, while snow remains cool due to high albedo.

Greenhouse Effect

The process by which greenhouse gases and clouds trap heat in Earth’s atmosphere by absorbing infrared radiation emitted from Earth’s surface. This natural effect keeps Earth warm enough to support life.

Urban Heat Island Effect

The phenomenon where urban areas experience higher temperatures than surrounding rural areas due to human activity, high population density, dark surfaces with low albedo, and limited vegetation.

Season

A period of the year characterized by distinct weather patterns and daylight conditions, caused by Earth’s axial tilt and its orbit around the Sun.

Subsolar Point

The point on Earth’s surface where the Sun’s rays strike directly overhead at a 90-degree angle. The subsolar point shifts between the Tropic of Cancer and the Tropic of Capricorn throughout the year, determining the solar altitude at different latitudes.

Solar Altitude

The angle of the Sun above the horizon at noon. Higher solar altitude means more direct sunlight and warmer temperatures.

Solstice

The time of year when one hemisphere is tilted most toward or away from the Sun.

Summer (June) Solstice

Occurs when the North Pole is tilted most toward the Sun, resulting in the longest day of the year in the Northern Hemisphere.

Winter (December) Solstice

Occurs when the South Pole is tilted most toward the Sun, resulting in the shortest day of the year in the Northern Hemisphere.

Equinox

The time of year when the Sun’s rays shine directly on the Equator, resulting in nearly equal hours of day and night worldwide.

Spring (March) Equinox

Marks the beginning of spring in the Northern Hemisphere.

Autumn (September) Equinox

Marks the beginning of fall in the Northern Hemisphere.