WHY IS THE SKY BLUE?

RADIATION

•Radiation is the direct transfer of energy by electromagnetic waves.• Infrared radiation has wavelengths that are longer than wavelengths for red light. (the red of ROY G BIV) Not visible, but can be felt as heat.•Ultraviolet radiation has wavelengths that are shorter than wavelengths for violet light (the violet end of ROY G BIV). It too is invisible, and can cause sunburns. In your textbook, cut out the picture of the electromagnetic spectrum on page 615 and glue into your comp book. Label visible light, infrared and ultraviolet radiation.

WHY IS THE SKY BLUE?

What you need:

•a clear, straight-sided drinking glass, or clear plastic or glass jar•water, milk, measuring spoons, flashlight•a darkened room

WHY IS THE SKY BLUE?

What to do:• Fill the glass or jar about 2/3 full of water (about 8 - 12 oz. or 250 - 400 ml).• Add 1/2 to 1 teaspoon (2 - 5 ml) milk and stir.• Take the glass and flashlight into a darkened room. 1. Hold the flashlight above the surface of the water and observe the water in the glass from the side. • In your comp book, describe what you see.

2. Now, hold the flashlight to the side of the glass and look through the water directly at the light. • In your comp book, describe what you see.

3. Put the flashlight under the glass and look down into the water from the top. • In your comp book, describe what you see.

WHY IS THE SKY BLUE?

•Look at your observations for each step. Discuss with your table why you think those observations happened.

WHY IS THE SKY BLUE?1. The first trial should have had a slight bluish tint.

2. The second trial should have had a slightly reddish tint.

3. The third trial should have had a deeper reddish tint.

What happened:

• The small particles of milk suspended in the water scattered the light from the flashlight, just like the dust particles and gas molecules in the air scatter sunlight. When the light shines in the top of the glass, the water looks blue because you see blue light scattered to the side.

When you look through the water directly at the light, it appears red (like a sunset or sunrise) because some of the blue was removed by scattering.

Why is the Sky Blue?• As sunlight enters the atmosphere, gas

molecules scatter some of the sun’s white light into its different colors, like a prism.

• The closer the wavelength of a light wave is to the size of the air molecule, the better that color of light is scattered.

• Blue light waves are the closest in size to atmospheric molecules so they are scattered most intensely.

Why are sunsets red?

• As the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered.

• Thus, different amounts of the shorter wavelength colors are scattered out. You see the longer wavelengths, and the sky appears red, pink or orange.

WHAT HAPPENS TO THE RADIATION THAT REACHES EARTH?

THE BREAKDOWN

•Fifty percent of the energy that reaches Earth’s surface is absorbed by land and water and changed into heat which then can be radiated back in to the air. (infrared radiation) •25% is reflected by clouds, dust, and gases in the atmosphere•20% is absorbed by gas and particles in the atmosphere•About 5% is reflected by the surface back into the atmosphere

WHAT HAPPENS TO THE RADIATION THAT REACHES

EARTH?

•The greenhouse effect- a natural process where the gasses in the atmosphere hold heat in. It keeps Earth at a comfortable temperature for most living things