Radiation is the transfer of energy through air and space by light waves (visible, ultraviolet and infrared waves).
Why do I care? Radiation from the sun sustains life on Earth and provides energy needed for plants and crops to grow for us to eat. The energy from the sun can be transformed into many other useable energy sources necessary for humans and plants to thrive.
|Figure A: Radiation From the Sun Hitting Earth|
Unlike convection, radiation does not require any fluids in order to transport heat. The energy from the sun is one great example of radiation. The sun emits light in a broad range of wavelengths which all contain energy. These waves are also discussed in the climate section for energy balance. The waves are emitted from the sun and travel through space and hit the earth and other planets. Once the light waves hit the atmosphere and ground, the energy stored in the waves heats up the soil and air, allowing conduction and convection to occur and move energy around the earth/atmosphere system. [Note that this radiation is not the same as nuclear radioactivity, which is caused by transformation of atoms undergoing physical changes within naturally occurring rocks as well as nuclear power plants and bombs.]
|Figure B: Roasting Marshmallows by Radiation|
But the sun isnâ€™t the only thing that emits radiation. Radiation is given off by lightbulbs, fires, and anything that has a temperature. Even you glow, but in a wavelength that the human eye cannot see. All of us are brighter than we think!
One example of radiative heating is the fires that many homes used to (and may still do) use to keep warm during the winter. We donâ€™t have to touch the fire to feel its warmth (that would be conduction, and not recommended!). When we face the flames we feel the warmth of the fire on our faces due to the radiation being given off, even when we are too far away to feel the hot air blowing around the coals. Radiative heating from the sun warms the soil in spring and leads to the new growth of plants each year as seeds in the soil germinate.
How does this relate to agriculture?
|Figure C: Sunflowers Absorbing Radiation From the Sun|
|Image courtesy of Bridget Lassiter
Plants need to absorb energy from the sun in the form of solar radiation in order to grow (using a biochemical process called photosynthesis). Most leaf surfaces are created to soak up the maximum amount of radiation, and plants have a specific shape or structure in order to ensure that they are as efficient as possible in collecting sunlight. Over time, crop plants have been selected and bred in order to ensure that this shape is such that the plant can intercept as much radiation as possible. For example, corn hybrids have been selected over time to have leaves that are not as upright, but rather grow outward so that more surfaces of the leaf can intercept radiation. Also, some plants have the biological ability to change direction based upon the direction of the sun, called heliotropism. One flower capable of this is the common sunflower.
Most people are familiar with plants growing inside of greenhouses. Greenhouses have been used for many years to exploit solar radiation. People discovered that they could grow crops (such as pineapples) inside greenhouses, which essentially extended the growing season for crops. Before this, tropical crops could not be grown in temperate climates, but were instead shipped long distances, which made them very costly. The concept of a greenhouse (glasshouse) is that solar radiation passes through a clear material such as glass or plastic. The sunlight heats the air and soil inside of the greenhouse, and the plants can also intercept the radiation. The walls of the greenhouse keep the warm air inside from mixing with the cooler outside air. Greenhouses ensure that crops can be grown even when temperatures outside of the glasshouse might be cool.
Links to National Science Education Standards:
5th grade science: 5.P.3.1 : Explain the effects of the transfer of heat (either by direct contact or at a distance) that occurs between objects at different temperatures. (conduction, convection, radiation).
7th grade science: 7.E.1.5 : Explain the influence of convection, global winds, and the jet stream on weather and climatic conditions.
Earth Science: EEn.1.1.3 : Explain how the sun produces energy which is transferred to the Earth by radiation.
Physical Science: PSc. 3.1.1 : Explain thermal energy and its transfer.
Activities to accompany the information above:
Activity: Atmospheric Processes-Radiation (Link to original activity.)
Description: This activity will assist students in understanding how objects gain energy through radiation. Students will record temperatures over a certain period for different colors of materials and develop an understanding of how the earth receives and emits energy throughout the year. This activity could be set up as a demo for the class.
Relationships to topics: Radiation
Activity: The Earth's Energy Budget (Link to original activity.)
Description: This activity focuses on the forms of heat transfer that take place within the Earth's atmosphere. Students will develop an understanding of how things heat up and which things will heat up faster than others.
Relationships to topics: Earth's Energy Balance
Activity: Air Temperature Investigations (Link to original activity.)
Description: This activity focuses on the daily energy cycles of the earth from having students analyze data. One location is chosen for students to understand the fluctuation of temperature throughout a 24-hour period. Temperature is then compared to incoming solar radiation from the sun throughout the same time period and students will be able to form a relationship between the two observations.
Activity: Energy Webquest
Description: In this activity, students review several websites that walk them through the layers of the atmosphere and energy transfer in the atmosphere.