THE SUN AS A SOURCE OF ENERGY INTEGRATED SCIENCE GRADE 8 G-L

The Electromagnetic Spectrum

The Electromagnetic Spectrum The heat produced by the Sun travels from the Sun to the Earth via waves known as electromagnetic waves. These waves can vary greatly in their wavelength. Have you ever thrown a rock into a lake?

What happens when you throw a small pebble into the water What happens when you throw a small pebble into the water? The resulting ripples are small, and each wave is close to the next wave; they have a short wavelength. Now, consider what would happen if you threw a large boulder into the water. Instead of small ripples, you get large waves. These larger waves are spaced further apart from one another. Thus, they have a large wavelength.

Because the electromagnetic waves traveling to the Earth from the Sun come in a variety of lengths, scientists consider them to be a spectrum. Thus, we refer collectively to all these waves as the electromagnetic spectrum. The electromagnetic spectrum is a big word that simply refers to all the different sized waves of energy traveling outward from the Sun, as well as from many other objects in the Universe.

To better understand the electromagnetic spectrum, scientists break it into three separate categories or divisions. The shortest waves are called ultraviolet waves. The medium sized waves are called visible light waves, and the longest waves are called infrared waves. Even longer waves also are categorized into radio waves, microwaves, and so forth.

Waves measuring under 0.4 micrometers are referred to as ultraviolet. These short waves are extremely dangerous to living organisms. Long term exposure to ultraviolet radiation would seriously hurt and even kill most lifeforms on Earth, including humans.

The Sun produces a significant amount of ultraviolet waves. Fortunately, most of these waves never reach the surface of the Earth. They are either absorbed, or reflected and bounced away by molecules in the upper atmosphere.

Visible Light Waves Waves with a length of between 0.4 and 0.7 micrometers can be detected by the human eye. For this reason we call these waves visible light. As you look around the room, everything you see has these waves bouncing off of them. If they didn’t, you would not be able to see them. What your eyes pick up and turn into a picture in your brain are these visible light waves. The wavelengths detectible by the human eye represent only about 3% of the total electromagnetic spectrum. Shorter visible light wavelengths are bluer in colour, while longer visible light wavelengths are redder in colour.  

Infrared Waves Infrared waves are commonly referred to has heat rays. Heat is in fact infrared radiation. Hold your hand next to a hot stove. Do you feel the heat radiating off of the stove and traveling towards your hand? If our eyes could see infrared radiation, what would it look like? You would see anything that produces heat, including plants and animals, no matter how dark it was. On average, the Sun produces very little infrared radiation compared to the amount of ultraviolet radiation and visible light that it creates.

Shortwave and Longwave Radiation Visible light and ultraviolet radiation are commonly called shortwave radiation, while infrared radiation is referred to as longwave radiation. The Sun radiates energy mainly in the form of visible light, with small amounts of ultraviolet and infrared radiation.

The Earth produces virtually no visible light, or ultraviolet radiation. Almost all of the natural radiation created by the Earth is infrared, or heat. Thus, we refer to the terrestrial radiation as longwave radiation.

Radiation All objects radiate energy and heat, even your own body. However, the radiation coming from hotter objects is more intense than that coming from cooler objects. Radiation leaves an object in the form of waves.

As you stand in front of a camp fire holding your cold fingertips out in front of you, what do you feel? Slowly your fingers begin to warm up as they absorb the radiation coming from the fire. The infrared waves, or heat rays, leave the hot fire, and radiate out towards your hands.

An object that is especially good at radiating heat is referred to as a blackbody. Both the Sun and the Earth are excellent radiators, and as a result, both are considered blackbodies.