The sun is the primary energy source for planet earth, but how is heat transferred from the sun to the earth?
In this article, you’ll learn the processes that facilitate the heat transfer from the sun till you feel it on your skin on a sunny day.
The Sun is a scorching ball of mostly hydrogen and helium 93 million miles away.
The Sun radiates energy using electromagnetic waves, which travel quickly through space. This is the primary way heat transfers from the sun to the earth.
Since the earth is not in direct contact with the sun, its energy has to travel through the vacuum of space to reach this planet.
This is possible because the energy travels at a very high speed as electromagnetic radiation straight until it collides with something.
After the electromagnetic waves travel through the vacuum of space, they bounce off gas molecules in the atmosphere and eventually warm the planet.
It should be noted that this mode of heat transfer cannot occur when something is shielding the source of heat.
The temperature of Earth remains within a habitable range of 29.6 and 35.6 degrees F (88 and 96 degrees F.
This is because the planet absorbs just the right amount and type of radiation from the sun to maintain that temperature range.
Most sunlight is visible light, created when photons of different wavelengths strike the atmosphere.
The visible light spectrum ranges from the longest wavelengths of 740 nanometers to about 400 nm.
Instruments can detect light at all wavelengths other than the visible spectrum, but not by our eyes alone.
Visible Light and Heat
Most sunlight is a mix of red, orange, yellow, green, blue, and violet.
Visible light also makes up about half the energy that reaches Earth. Visible light passes through Earth’s atmosphere.
The temperature at the Sun’s surface is about 6,000 degrees Celsius.
The Sun’s energy is converted to thermal energy at the Earth’s surface, commonly called heat.
Heat is a form of energy that occurs when the matter in the shape of molecules vibrates.
Note: Light also strikes our atmosphere and bounces back into space or is reflected directly back to Earth by clouds, snow, and other objects.
Three types of energy reach the Earth from the sun in addition to visible light: ultraviolet radiation, infrared radiation, and radio waves.
Ultraviolet (UV) light and infrared radiation (IR, another name for heat radiation) are different in that one is electromagnetic and the other thermodynamic.
Ultraviolet radiation, electromagnetic radiation with a wavelength shorter than that of visible light, is emitted by the Sun.
This is in addition to infrared radiation, a form of radiation with a longer wavelength than that of visible light.
Dangers of UV Energy
The wavelengths of ultraviolet and infrared radiation are beyond the range of human sight and perception.
Ultraviolet light has short wavelengths. Infrared has long wavelengths; both can potentially be harmful to organisms that sense them.
Because of its short wavelengths, ultraviolet light can be dangerous to human skin because it can break chemical bonds.
A large dose of UV light will cause skin damage, including burning and cancer.
Infrared Radiation and Warmth
Infrared radiation has longer wavelengths than visible light and sometimes has a lower frequency than visible light waves.
Its wavelength is below the red, green, and blue wavelengths of visible light.
Infrared radiation is also emitted by all objects with a temperature that is greater than absolute zero.
Fact: Infrared can be felt as thermal energy or warmth, as your skin absorbs it.
Energy on Earth
The next step in understanding how heat is transmitted from the sun to the earth is to understand absorption.
While an enormous amount of solar energy strikes the surface of Earth each second, some of that energy is reflected into space.
The atmosphere absorbs about 20 percent of the solar radiation, which is then reradiated back into space as infrared radiation.
Oxygen, water vapor, and ozone absorb ultraviolet light.
2. Absorption In The Atmosphere
Water vapor and carbon dioxide in the troposphere absorb some infrared radiation from the Sun.
Light in the visible spectrum bounces off of objects when it strikes them. To be absorbed, it must first be converted to infrared radiation.
Note: Visible light passes through the atmosphere without being absorbed.
3. Thermal Energy Transfer
It is important to remember that there are three types of thermal energy transfer—radiation, conduction, and convection.
All three occur in the atmosphere.
While heat energy is transferred to the atmosphere in many ways, two kinds of processes occur.
By far, the essential function is convection, as air near Earth’s surface rises and falls with the daily and seasonal cycles of weather.
As the temperature of an object increases, its molecules move more quickly.
When they collide with an object at a lower temperature, they can convey their kinetic energy to the other entity. This is called thermal conduction.
Conduction is a form of heat transfer in which thermal energy moves from one atom or molecule to another by direct contact.
Atmospheric conduction of the sun’s heat occurs when the atmosphere comes in contact with Earth.
Fact: If you touched the surface of a pot of boiling water, thermal energy would pass through the pot and into your hand.
As heated air in the lower atmosphere rises (because it is less dense), it leaves behind cooler air, which descends to fill in the space left by the rising heated air.
This movement of air molecules combined with the capture of additional energy from solar radiation at higher altitudes drives atmospheric circulation patterns.
This is due to a phenomenon called “convection,” and it’s very crucial in how is heat transferred from the sun to the earth.
Convection is how warm air moves upward, carrying warmth and thermal energy with it.
6. Heat Convection and Circulating Air
As a result, the density of earthbound air decreases, causing less-dense air masses to rise and transfer thermal energy to higher altitudes.
Convection is a never-ending cycle that helps distribute and redistribute the sun’s heat in the atmosphere.
Fact: Circulating air creates different weather and climatic conditions in the world.
7. Latent Heat
Water covers most of the planet’s surface, is the only substance able to exist as a solid, liquid, and gas here on Earth.
Because of its chemical properties, it plays an essential role in our world.
Much of solar heat energy that reaches the earth is stored in water. Latent heat is the amount of energy required to change a water unit from one phase to another.
For example, when water changes from a solid state to a liquid state, specific energy is absorbed or released—this absorbed energy is latent heat.
The glass of a greenhouse converts sunlight into infrared energy.
It is transparent to visible light, but it is colorless or green to allow near-infrared light to pass through and reach the plants inside.
The IR warms the interior of the greenhouse.
Solar Heat and Greenhouse Gases
Some gases in Earth’s atmosphere perform the same role as glass in a greenhouse.
These gases are called greenhouse gases, and they trap the sun’s heat in the atmosphere.
The greenhouse effect is a warming of Earth’s atmosphere due to radiation from the sun directed back toward Earth by certain gases in the atmosphere.
Water vapor, carbon dioxide, and methane are the most noteworthy gases that trap infrared best.
Understanding how is heat transferred from the sun to the earth helps us appreciate how the various processes on our planet unfold.
This is because almost all energy on earth originates from the sun, making the sun our parent source of heat energy.
It’s worth noting that as you move into cold air from a warm environment, your body releases some heat and your breath shows it.
In the same way, plants release heat from their leaves into the atmosphere.