WHY IS THE SKY BLUE?

On a clear sunny day, the sky above us looks bright blue. In the evening, the sunset puts on a brilliant show of reds, pinks and oranges. Why is the sky blue? What makes the sunset red?

To answer these questions, we must learn about light, and the Earth's atmosphere.

THE ATMOSPHERE

The atmosphere is the mixture of gas molecules and other materials surrounding the earth. It is made mostly of the gases nitrogen (78%), and oxygen (21%). Argon gas and water (in the form of vapor, droplets and ice crystals) are the next most common things. There are also small amounts of other gases, plus many small solid particles, like dust, soot and ashes, pollen, and salt from the oceans.

The composition of the atmosphere varies, depending on your location, the weather, and many other things. There may be more water in the air after a rainstorm, or near the ocean. Volcanoes can put large amounts of dust particles high into the atmosphere. Pollution can add different gases or dust and soot.

The atmosphere is densest (thickest) at the bottom, near the Earth. It gradually thins out as you go higher and higher up. There is no sharp break between the atmosphere and space.

LIGHT WAVES

Light is a kind of energy that radiates, or travels, in waves. Many different kinds of energy travel in waves. For example, sound is a wave of vibrating air. Light is a wave of vibrating electric and magnetic fields. It is one small part of a larger range of vibrating electromagnetic fields. This range is called the electromagnetic spectrum.

Electromagnetic waves travel through space at 299,792 km/sec (186,282 miles/sec). This is called the speed of light.

The energy of the radiation depends on its wavelength and frequency. Wavelength is the distance between the tops (crests) of the waves. Frequency is the number of waves that pass by each second. The longer the wavelength of the light, the lower the frequency, and the less energy it contains.

COLORS OF LIGHT

Visible light is the part of the electromagnetic spectrum that our eyes can see. Light from the sun or a light bulb may look white, but it is actually a combination of many colors. We can see the different colors of the spectrum by splitting the light with a prism. The spectrum is also visible when you see a rainbow in the sky.

The colors blend continuously into one another. At one end of the spectrum are the reds and oranges. These gradually shade into yellow, green, blue, indigo and violet. The colors have different wavelengths, frequencies, and energies. Violet has the shortest wavelength in the visible spectrum. That means it has the highest frequency and energy. Red has the longest wavelength, and lowest frequency and energy.

LIGHT IN THE AIR

Light travels through space in a straight line as long as nothing disturbs it. As light moves through the atmosphere, it continues to go straight until it bumps into a bit of dust or a gas molecule. Then what happens to the light depends on its wave length and the size of the thing it hits.

Dust particles and water droplets are much larger than the wavelength of visible light. When light hits these large particles, it gets reflected, or bounced off, in different directions. The different colors of light are all reflected by the particle in the same way. The reflected light appears white because it still contains all of the same colors.

Gas molecules are smaller than the wavelength of visible light. If light bumps into them, it acts differently. When light hits a gas molecule, some of it may get absorbed. After awhile, the molecule radiates (releases, or gives off) the light in a different direction. The color that is radiated is the same color that was absorbed. The different colors of light are affected differently. All of the colors can be absorbed. But the higher frequencies (blues) are absorbed more often than the lower frequencies (reds). This process is called Rayleigh scattering. (It is named after Lord John Rayleigh, an English physicist, who first described it in the 1870's.)

WHY IS THE SKY BLUE?

The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.

However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.

As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.

THE BLACK SKY AND WHITE SUN

On Earth, the sun appears yellow. If you were out in space, or on the moon, the sun would look white. In space, there is no atmosphere to scatter the sun's light. On Earth, some of the shorter wavelength light (the blues and violets) are removed from the direct rays of the sun by scattering. The remaining colors together appear yellow.

Also, out in space, the sky looks dark and black, instead of blue. This is because there is no atmosphere. There is no scattered light to reach your eyes.

WHY IS THE SUNSET 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. As less reaches you directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes.

The sky around the setting sun may take on many colors. The most spectacular shows occur when the air contains many small particles of dust or water. These particles reflect light in all directions. Then, as some of the light heads towards you, different amounts of the shorter wavelength colors are scattered out. You see the longer wavelengths, and the sky appears red, pink or orange.

---

Learn Science The Easy Way With
Science Made Simple.

Click here to try it now
Completely Risk Free!

---

LEARN MORE ABOUT:THE ATMOSPHERE

WHAT IS THE ATMOSPHERE?

The atmosphere is the mixture of gases and other materials that surround the Earth in a thin, mostly transparent shell. It is held in place by the Earth's gravity. The main components are nitrogen (78.09%), oxygen (20.95%), argon (0.93%), and carbon dioxide (0.03%). The atmosphere also contains small amounts, or traces, of water (in local concentrations ranging from 0% to 4%), solid particles, neon, helium, methane, krypton, hydrogen, xenon and ozone. The study of the atmosphere is called meteorology.

Life on Earth would not be possible without the atmosphere. Obviously, it provides the oxygen we need to breath. But it also serves other important functions. It moderates the planet's temperature, reducing the extremes that occur on airless worlds. For example, temperatures on the moon range from 120 °C (about 250 °F) in the day to -170 °C (about -275 °F) at night. The atmosphere also protects us by absorbing and scattering harmful radiation from the sun and space.

Of the total amount of the sun's energy that reaches the Earth, 30% is reflected back into space by clouds and the Earth's surface. The atmosphere absorbs 19%. Only 51% is absorbed by the Earth's surface.

We are not normally aware of it but air does have weight. The column of air above us exerts pressure on us. This pressure at sea level is defined as one atmosphere. Other equivalent measurements you may hear used are 1,013 millibars, 760 mm Hg (mercury), 29.92 inches of Hg, or 14.7 pounds/square inch (psi). Atmospheric pressure decreases rapidly with height. Pressure drops by a factor of 10 for every 16 km (10 miles) increase in altitude. This means that the pressure is 1 atmosphere at sea level, but 0.1 atmosphere at 16 km and only 0.01 atmosphere at 32 km.

The density of the lower atmosphere is about 1 kg/cubic meter (1 oz./cubic foot). There are approximately 300 billion billion (3 x 10**20, or a 3 followed by 20 zeros) molecules per cubic inch (16.4 cubic centimeters). At ground level, each molecule is moving at about 1600 km/hr (1000 miles/hr), and collides with other molecules 5 billion times per second.

The density of air also decreases rapidly with altitude. At 3 km (2 miles) air density has decreased by 30%. People who normally live closer to sea level experience temporary breathing difficulties when traveling to these altitudes. The highest permanent human settlements are at about 4 km (3 miles).

LAYERS OF THE ATMOSPHERE

The atmosphere is divided into layers based on temperature, composition and electrical properties. These layers are approximate and the boundaries vary, depending on the seasons and latitude. (The boundaries also depend on which "authority" is defining them.)

LAYERS BASED ON COMPOSITION

Homosphere

· The lowest 100 km (60 miles), including the Troposphere, Stratosphere and Mesosphere.

· Contains 99% of the atmosphere's mass.

· Molecules do not stratify by molecular weight.

· Although small local variations exist, it has a relatively uniform composition, due to continuous mixing, turbulence and eddy diffusion.

· Water is one of two components that is not equally distributed. As water vapor rises, it cools and condenses, returning to earth as rain and snow. The Stratosphere is extremely dry.

· Ozone is another molecule not equally distributed. (Read about the ozone layer in the Stratosphere section below.)

Heterosphere

· Extends above homosphere, including the Thermosphere and Exosphere.

·Stratified (components are separated in layers) based on molecular weight. The heavier molecules, like nitrogen and oxygen, are concentrated in the lowest levels. The lighter ones, helium and hydrogen, predominate higher up.

LAYERS BASED ON ELECTRICAL PROPERTIES

Neutral atmosphere

· Below about 100 km (60 miles)

Ionosphere

· Above about 100 km

· Contains electrically charged particles or ions, created by the absorption of UV (ultraviolet) light.

· The degree of ionization varies with altitude.

· Different layers reflect long and short radio waves. This allows radio signals to be sent around the curved surface of the earth.

· The Aurora Borealis and Aurora Australis (the Northern and Southern Lights) occur in this layer.

· The Magnetosphere is the upper part of the ionosphere, extending out to 64,000 km (40,000 miles.) It protects us from the high energy, electrically charged particles of the solar wind, which are trapped by the Earth's magnetic field.

LAYERS BASED ON TEMPERATURE

Troposphere - Height depends on the seasons and latitude. It extends from ground level up to about 16 km (10 miles) at the equator, and to 9 km (5 miles) at the North and South Poles.

· The prefix "tropo" means change. Changing conditions in the Troposphere result in our weather.

· Temperature decreases with increasing altitude. Warm air rises, then cools and falls back to Earth. This process is called convection, and results in huge movements of air. Winds in this layer are mostly vertical.

· Contains more air molecules than all the other layers combined.

Stratosphere - Extends out to about 50 km (30 miles)

· The air is very thin.

· The prefix "strato" is related to layers, or stratification.

· The bottom of this layer is calm. Jet planes often fly in the lower Stratosphere to avoid bad weather in the Troposphere.

· The upper part of the Stratosphere holds the high winds known as the jet streams. These blow horizontally at speeds up to 480 km/hour (300 miles/hour)

· Contains the "ozone layer" located between 15 - 40 km ( 10 - 25 miles) above the surface. Although the concentration of ozone is at most 12 parts per million (ppm), it is very effective at absorbing the harmful ultraviolet (UV) rays of the sun and protecting life on Earth. Ozone is a molecule made of three oxygen atoms. The oxygen molecule we need to breathe contains two oxygen atoms.

· The temperature is cold, about -55 °C (-67 °F) in the lower part, and increases with increasing altitude. The increase is caused by the absorption of UV radiation by the oxygen and ozone.

· The temperature increase with altitude results in a layering effect. It creates a global "inversion layer", and reduces vertical convection.

Mesosphere - Extends out to about 100 km (65 miles)

· Temperature decreases rapidly with increasing altitude.

Thermosphere - Extends out to about 400 km ( 250 miles)

· Temperature increases rapidly with increasing altitude, due to absorption of extremely short wavelength UV radiation.

· Meteors, or "shooting stars," start to burn up around 110-130 km (70-80 miles) above the earth.

Exosphere -Extends beyond the Thermosphere hundreds of kilometers, gradually fading into interstellar space.

· Density of the air is so low that the normal concept of temperature looses its meaning.

· Molecules often escape into space after colliding with one another.

---

I CAN READ

Why is the sky blue?

Light is a kind of energy that can travel through space. Light from the sun or a light bulb looks white, but it is really a mixture of many colors. The colors in white light are red, orange, yellow, green, blue and violet. You can see these colors when you look at a rainbow in the sky.

The sky is filled with air. Air is a mixture of tiny gas molecules and small bits of solid stuff, like dust.

As sunlight goes through the air, it bumps into the molecules and dust. When light hits a gas molecule, it may bounce off in a different direction. Some colors of light, like red and orange, pass straight through the air. But most of the blue light bounces off in all directions. In this way, the blue light gets scattered all around the sky.

When you look up, some of this blue light reaches your eyes from all over the sky. Since you see blue light from everywhere overhead, the sky looks blue.

In space, there is no air. Because there is nothing for the light to bounce off, it just goes straight. None of the light gets scattered, and the "sky" looks dark and black.

---

PROJECTS TO DO TOGETHER

SAFETY NOTE: Please read all instructions completely before starting. Observe all safety precautions.

PROJECT 1 - Split light into a spectrum

What you need:

a small mirror, a piece of white paper or cardboard, water

a large shallow bowl, pan, or plastic shoebox

a window with direct sunlight coming in, or a sunny day outdoor

What to do:

1. Fill the bowl or pan about 2/3 full of water. Place it on a table or the floor, directly in the sunlight. (Note: the direct sunlight is important for this experiment to work right.)
2. Hold the mirror under water, facing towards the sun. Hold the paper above and in front of the mirror. Adjust the positions of the paper and mirror until the reflected light shines on the paper. Observe the colored spectrum.

What happened: The water and mirror acted like a prism, splitting the light into the colors of the spectrum. (When light passes from one medium to another, for example from air to water, its speed and direction change. [This is called refraction, and will be discussed in a future issue.] The different colors of light are affected differently. Violet light slows the most, and bends the most. Red light slows and bends the least. The different colors of light are spread out and separated, and we can see the spectrum.)

PROJECT 2 - Sky in a jar

What you need:

a clear, straight-sided drinking glass, or clear plastic or glass jar

water, milk, measuring spoons, flashlight

a darkened room

What to do:

1. Fill the glass or jar about 2/3 full of water (about 8 - 12 oz. or 250 - 400 ml)
2. Add 1/2 to 1 teaspoon (2 - 5 ml) milk and stir.
3. Take the glass and flashlight into a darkened room.
4. Hold the flashlight above the surface of the water and observe the water in the glass from the side. It should have a slight bluish tint. Now, hold the flashlight to the side of the glass and look through the water directly at the light. The water should have a slightly reddish tint. Put the flashlight under the glass and look down into the water from the top. It should have a deeper reddish tint.

What happened: The small particles of milk suspended in the water scattered the light from the flashlight, like the dust particles and 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 because some of the blue was removed by scattering.

PROJECT 3 -Mixing colors

You need:

a pencil, scissors, white cardboard or heavy white paper

crayons or markers, a ruler

a small bowl or a large cup (3 - 4 inch, or 7 - 10 cm diameter rim)

a paper cup

What to do:

1. Use the bowl to trace a circle onto a piece of white cardboard and cut it out. With the ruler, divide it into six approximately equal sections.
2. Color the six sections with the colors of the spectrum as shown. Try to color as smoothly and evenly as possible.
3. Poke a hole through the middle of the circle and push the pencil part of the way through.
4. Poke a hole in the bottom of the paper cup, a little bit larger than the diameter of the pencil. Turn the cup upside down on a piece of paper, and put the pencil through so the point rests on the paper on a table. Adjust the color wheel's position on the pencil so that it is about 1/2 inch (1 - 2 cm) above the cup.
5. Spin the pencil quickly and observe the color wheel. Adjust as necessary so that the pencil and wheel spin easily.

What happened: The colors on the wheel are the main colors in white light. When the wheel spins fast enough, the colors all appear to blend together, and the wheel looks white. Try experimenting with different color combinations.

Which affects evaporation the most.. air temperature, water temperature or wind speed?

FACTORS AFFECTING RATE OF EVAPORATION

This experiment will show you how factors such as temperature, wind, and surface area affect the rate of evaporation.

WHAT YOU NEED:

pan balance

sponges of different sizes

scissors

plastic sandwich bag

spotlight

hot water

cold water

electric fan

jar lid

WHAT TO DO:

1. Using the materials listed above, design an experiment to see how wind, temperature, and surface area affect the rate of evaporation. Make a prediction about the effect each factor will have on the evaporation rate.

2. Next, conduct the experiment using the materials provided to test your predictions. Record all your steps for carrying out the experiment.

NOTE: Every factor should be the same except the factor that you are testing. For example if you are testing the affect of wind on evaporation rates, the sponges should be the same size, and they should be exposed to the same temperatures. The only thing that should be different is the exposure to wind.

WHAT NOW:

Create a chart showing the results of your experiment. Make sure you include the results for all three factors (wind, temperature, and surface area).

What does a barometer do? Make your own barometer to demonstrate how it can be used

What is air pressure? Did you know you can make something that will measure air pressure? You can actually do a bit of weather predicting from a simple made-at-home piece of equipment.

What do I Need?

An empty coffee can

A large balloon

A large rubber band, one that will fit snugly around the coffee can

A pin

Glue

Straw

Paper

What Do I Do?

First, as an experiment, blow up the balloon. Think about how the more air there is in the balloon, the more pressure it exerts outward. This is what makes the balloon bigger as you blow it up.

Cut a large piece of the balloon and stretch it over the coffee can. Hole the balloon in place with a rubber band stretched around the can, over the balloon. Make sure there is a tight seal around the rubber band. Any air leaks around the piece of balloon will affect how well your barometer will work.

Use a little glue (not hot melt) and attach the straw to the piece of balloon over the can. Then use a little more glue and attach the pin to the other end of the straw (see diagram.)

Take a piece of paper and place some regularly spaced lines on it.

Set up the can and paper as shown in the diagram. Outside will work better than inside.

Using Your Barometer

Make several daily recording for about a week. Make notes about the weather when you take the readings. What do you notice about the readings and the weather? Compare the readings of the barometer outside with those of a barometer inside.

How Does It Work?

How are clouds formed?

Materials Needed:

-1 Clear plastic 2-liter soda bottle (remove label)
-1 Sheet black construction paper
-Water
-Matches (Be sure to have adult supervision)

Instructions:

Step 1: Pour 2 inches of very hot tap water into the 2-liter bottle.

Step 2: Place your mouth over the opening and blow into it to ensure the bottle is fully expanded. Immediately seal the bottle tightly.

Step 3: Shake the bottle vigorously for one minute. This will distribute water molecules in the air.

Step 5: With adult supervision, light a match. Let it burn for two seconds, then drop it into the bottle. Quickly recap the bottle.

Step 6: Lay the bottle on its side with the black paper behind it. Press hard on the bottle for ten seconds. The bottle is strong, so don't be afraid to really push hard. Release, observe, and repeat until a cloud forms.

Step 7: When the cloud has formed, quickly unscrew the cap. You should see the cloud escape from the bottle. If not, give the bottle a light squeeze.

---

Scientific Principle:

By following the steps, you have created the conditions necessary for cloud formation: water vapor in the air, smoke particles for water to collect on, and cooling of the air by lowering the air pressure within the bottle. Voila! Instant cloud formation. Clouds form when condensation collects dust particles, which you provided with the smoke from the match.

Explain the different types of clouds and how they are formed

Graphic by: Yiqi Shao

A cloud is a visible aggregate of tiny water droplets and/or ice crystals suspended in the atmosphere and can exist in a variety of shapes and sizes. Some clouds are accompanied by precipitation; rain, snow, hail, sleet, even freezing rain. The purpose of this module is to introduce a number of cloud classifications, different types of precipitation, and the mechanisms responsible for producing them. The Clouds and Precipitation module has been organized into the following sections:

Sections

Development The importance of rising motion and the mechanisms responsible for lifting the air. The States of Water solid, liquid, gas Water is known to exist in three different states; as a solid, liquid or gas. Clouds, snow, and rain are all made of up of some form of water. A cloud is comprised of tiny water droplets and/or ice crystals, a snowflake is an aggregate of many ice crystals, and rain is just liquid water. Water existing as a gas is called water vapor. When referring to the amount of moisture in the air, we are actually referring to the amount of water vapor. If the air is described as "moist", that means the air contains large amounts of water vapor. Common sources of moisture for the United States are the warm moist air masses that flow northward from the Gulf of Mexico and western Atlantic Ocean as well as the moist Pacific air masses brought onshore by the westerlies. As cyclones move eastward from the Rocky Mountains, southerly winds ahead of these storm systems transport the warm moist air northward. Moisture is a necessary ingredient for the production of clouds and precipitation. Cloud Types High, middle and low-level clouds, vertically developed clouds, plus some less common cloud types. Clouds are classified into a system that uses Latin words to describe the appearance of clouds as seen by an observer on the ground. The table below summarizes the four principal components of this classification system (Ahrens, 1994). Latin Root Translation Example cumulus stratus cirrus nimbus heap layer curl of hair rain fair weather cumulus altostratus cirrus cumulonimbus Further classification identifies clouds by height of cloud base. For example, cloud names containing the prefix "cirr-", as in cirrus clouds, are located at high levels while cloud names with the prefix "alto-", as in altostratus, are found at middle levels. This module introduces several cloud groups. The first three groups are identified based upon their height above the ground. The fourth group consists of vertically developed clouds, while the final group consists of a collection of miscellaneous cloud types. Photograph by: Knupp High-Level Clouds High-level clouds form above 20,000 feet (6,000 meters) and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals. High-level clouds are typically thin and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon. Photograph by: Holle Mid-Level Clouds The bases of mid-level clouds typically appear between 6,500 to 20,000 feet (2,000 to 6,000 meters). Because of their lower altitudes, they are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough. Low-level Clouds Low clouds are of mostly composed of water droplets since their bases generally lie below 6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may also contain ice particles and snow. Photograph by: Holle Vertically Developed Clouds Probably the most familiar of the classified clouds is the cumulus cloud. Generated most commonly through either thermal convection or frontal lifting, these clouds can grow to heights in excess of 39,000 feet (12,000 meters), releasing incredible amounts of energy through the condensation of water vapor within the cloud itself. Photograph by: Holle Other Cloud Types Finally, we will introduce a collection of miscellaneous cloud types which do not fit into the previous four groups. Classifications Last Update: 07/09/97 High-Level Clouds Cloud types include: cirrus and cirrostratus. Mid-Level Clouds Cloud types include: altocumulus, altostratus. Low-Level Clouds Cloud types include: nimbostratus and stratocumulus. Clouds with Vertical Development Cloud types include: fair weather cumulus and cumulonimbus. Other Cloud Types Cloud types include: contrails, billow clouds, mammatus, orographic and pileus clouds. Precipitation Rain, snow, hail, sleet and freezing rain. Photograph by: Norene McGhiey When cloud particles become too heavy to remain suspended in the air, they fall to the earth as precipitation. Precipitation occurs in a variety of forms; hail, rain, freezing rain, sleet or snow. This portion of the Clouds and Precipitation module focuses on precipitation and has been organized into the following sections. Sections Latest Update: 07/21/97 Rain and Hail Atmospheric conditions that lead to the development of rain and hail. Freezing Rain A detailed look at freezing rain, associated dangers and the conditions that lead to its development. Sleet Atmospheric conditions that lead to the development of sleet. Snow Atmospheric conditions that lead to the development of snow. Acknowledgments Those who contributed to the Precipitation sections of the Clouds and Precipitation module. The navigation menu (left) for this section is called "Precipitation" and the menu items are arranged in a recommended sequence, beginning with this introduction. In addition, this entire web server is accessible in both "graphics" and "text"-based modes, a feature controlled from the blue "User Interface" menu (located beneath the black navigation menus). More information about the user interface options, the navigation system, or WW2010 in general is accessible from About This Server. Acknowledgments Those who contributed to the development of this module. WW2010 Personnel (Clouds): Steven E. Hall - Content Developer and Editor - Scanned in slides, constructed original text and diagrams. Responsible for new layout, organization and cross linking of helper pages. Implemented text and graphics modifications as recommended by the Content Reviewers. John Walsh - Content Reviewer - Professor of Atmospheric Sciences who edited module text and diagrams for scientific accuracy. Ken Beard - Content Reviewer - Professor of Atmospheric Sciences who edited module text and diagrams for scientific accuracy. Mythili Sridhar - Graphics Assistant- Graphically enhanced previous version of this module. Yiqi Shao - HTML Programmer and Graphics Assistant - Helped with the integration of this module into the WW2010 format and constructed home page graphic.

The navigation menu (left) for this module is called "Clouds, Precipitation" and the menu items are arranged in a recommended sequence, beginning with this introduction. In addition, this entire web server is accessible in both "graphics" and "text"-based modes, a feature controlled from the blue "User Interface" menu (located beneath the black navigation menus). More information about the user interface options, the navigation system, or WW2010 in general is accessible from About This Server.

Does the level of precipitation differ in various parts of the United States?

Hypothesis	We predict that there will be more snow in Evanston than in California, Kentucky, southern Illinois, and Alabama. We think Pennsylvania will have the most snow and California the least. We predict that there will be the most rain in California and that Alabama will also have a lot of rain. We think Alabama will have the least amount of snow. We predict that Kentucky will have a lot of rain but little snow. We think there will be different amounts of rain in different places in Evanston and Skokie.
Abstract	We predicted that there would be different amounts of precipitation around the United States during a given month. Further, we felt that there would even be different amounts of precipitation in the different areas of Evanston and Skokie that we live in. We collected data of precipitation in different parts of the country via e mail. Each week, each classroom sent us the amount and the type of precipitation that fell during the previous week. Additionally, we collected rain data at our own homes each week with precipitation gauges we had made. We used the medians of our individual weekly data for our data included in this experiment report. There were different amounts of precipitation across the country as well as in our own area. Because of El Nino, we had no snow during the entire month of February while California had a great deal. If we performed this experiment again, we would try to be more accurate in our collection of our own data. We would also try to get more participants.
Materials	rain gauge, 2 liter pop bottles, e mail
Procedure	Recruit students from other schools in the country to measure the amount of precipitation at their school each week. Construct rain gauges for each student in Room 204 to take home and install in a safe, open place. Measure the amount of rainfall and/or snow each week and record the data.Check e mail for data received from each of the participating schools. RESEARCH: A standard rain gauge is an instrument that measures the amount of rain that falls in a certain place over a period of time. The National Weather Service uses a rain gauge that is shaped like a cylinder and has a removable cover. Inside the cylinder, is a long, narrow tube where the rain falls and is subsequently measured. The top of the tube is connected with a funnel. The rain falls into the funnel and then into the tube. The mouth of the funnel has an area ten times as large as the tube. Therefore, if an inch of rain falls into the funnel, it would fill ten inches of the tube. The rainfall is measured with a ruler. After it is measured, its tube is emptied out and the results are recorded. The rain gauge that we used at school is shaped like a rectangular prism on three sides and the fourth side is on an angle. We used the metric system for measurements. The rain gauges we made for our homes and that classes around the country that collected data for us used were made out of 2 liter plastic soda pop bottles. We dug them into the ground near our homes and emptied them each week after we measured the rainfall. There was no measurable snow during the entire month of February in the area of our school. (Alex) El Nino is Spanish for “Christ Child”. Fishermen in Peru and Ecuador began using this term to refer to the coastal warming that began around the Christmas season and lasted for several months. It has developed into a term meaning an “abnormal warming event.” The winter of 1982-83 was the strongest El Nino this century and not only affected the South American coast, but the entire world also. This year, El Nino has shown its effect on Evanston. (Russell, Joe) Sacramento, California--a warm area which is the capital of California. The Sacramento River runs through the town into the Pacific Ocean. They had so much rain in February that they had to close the schools. (Eugene, Eliza, and Megan) Spanish Fort, Alabama--located about ten minutes from Mobile and three hours from New Orleans. Generally, they have many hurricanes and tornadoes in March and April. They also have many tornadoes in the late summer. They are the wettest city in the United States. (Danny, Amy) Ulster, Pennsylvania----located in northeast Pennsylvania, twelve miles from the New York border. It is a rural area with many farms. Their rain gauge got buried when they had 45 cm of snow. (Russell, Alex) Cynthiana, Kentucky--a rural town located in the bluegrass area of Kentucky. They have beef cattle, sheep, chicken, and tobacco farming. There is also coal in the area. During February, they had 120 cm of rain. They generally get snow here, but not as much as they got all at once (53.5 cm). (Kasha, Ryan) Peoria, Illinois--a city in central Illinois. It is near the Senachwine Lake. Peoria is an important farming area in the center of Illinois. The area is called the Till Plains. It was odd that it snowed very little during February, and one of the weeks had no precipitation at all. (Cara, Joe) Evanston, Illinois--large city next to Chicago. It is a completely urban area. It was odd that there was only rain in February, and very little at that. Generally, we expect snow at this time of year. Click to view map.
Results	Median Amounts of Rain Data Collected at Our Homes in Evanston/Skokie, IL Timber Ridge Magnet School, Skokie, IL--all rain Spanish Fort School, Spanish Fort, Alabama (Erica, Danny, Amy) Hollis Grade School, Peoria, Illinois (Cara, Joe, Stacie) Sheshequin-Ulster Elementary School, Ulster, Pennsylvania (Micky, Alex) Taylor Street School,Sacramento, California (Mean, Eugene) Southside Elementary School, Cynthiana, KY (Kasha, Ryan) Total Precipitation at all Sites Measured in February, 1998 (Laurel, Nat Matthew, Ben) We discovered that our hypothesis about snow and rain were wrong as to where the most snow and/or rain would fall. However, our hypothesis about there being different amounts in our neighborhoods and across the country were accurate. Evanston had the least amount of precipitation of all the cities and Cynthiana, Kentucky had the most. California did not have the most amount of rain, and Spanish Fort, Alabama did not have the least. There were different amounts of precipitation in different parts of Skokie and Evanston. There were very different amounts of precipitation in different parts of the country and even from week to week. The amounts of rain varied from a low of 1.9 cm in Spanish Fort, Alabama to a high of 69 cm in Cynthiana, Kentucky. There was no snow in Sacramento, California, Spanish Fort, Alabama, nor in Evanston, Illinois. However, Cynthiana, Kentucky recorded 53.5 cm of snow during the same month, and we had predicted that Evanston would have more snow than they would.
Conclusion	El Nino made the weather during the month of February very strange. In Evanston, we had no snow, which was very unusual for the month of February. However, there was a huge amount of snow in California, and floods occurred in both Kentucky and California.
Bibliography & Links	Blair, Randee, Fourth Grade Teacher, Timber Ridge Magnet School, Skokie, IL DeMers, Elaine, Fourth Grade Teacher, Taylor Street School, Sacramento, CA Heald, Blair, Teacher of Gifted Classes K-7, Spanish Fort School, Spanish Fort, AL Hughes, Kathy, Kindergarten Teacher, Sheshequin-Ulster Elementary School, Ulster, PA McDaniel, DeAnna, Fourth Grade Teacher, Southside Elementary School, Cynthiana, KY Titus, Nancy, Second Grade Teacher, Hollis Grade School, Peoria, IL Web Site: http://www.eduzone.com/tips/science/showtip3.htm Web Site: http://www.pbs.org/wgbn/novulehim/resources/glossary.html Web Site: http://www.pmel.noaa.gov/toga-tao/el-nino-report.html#part 2 World Book Encyclopedia, Vol. 16, pp. 126-127, 1996.

Does the amount of moisture in the atmosphere vary from place to place?

Measuring Cloud Cover

During the day the sun is always shining, so the amount of sunshine reaching the ground depends on the amount and duration of any cloud cover. The amount of cloud cover is usually given in units called oktas.

Each okta represents one eighth of the sky covered by cloud. Clear sky /1 okta / 2 oktas / 3 oktas / 4 oktas / 5 oktas / 6 oktas / 7 oktas / Overcast

Using a Cloud Mirror

You can use a cloud mirror to simply measure oktas. Divide a large mirror into a grid with 16 equal squares using a dark crayon. Lay the mirror on the ground somewhere you can see the whole sky.

Count the number of grid squares, or fractions of squares with cloud in them. Divide that number by two to convert sixteenths into oktas.

http://www.bbc.co.uk/weather/weatherwise/activities/weatherstation/cloud_measuring.shtml

Measuring Humidity

There is water vapour in the air at all times. Humidity is the amount of water vapour present in the air and we can measure this using a hygrometer.

Relative humidity is the ratio of the actual amount of moisture in the atmosphere to the amount of moisture the atmosphere can hold. Therefore, a relative humidity of 100% means the air can hold no more water (rain or dew is likely), and a relative humidity of 0% indicates there is no moisture in the atmosphere. Relative humidity is used by meteorologists to help predict the weather, by pathologists to predict disease development on plants, and by agricultural scientists to estimate evapotranspiration

Relative humidity, combined with air temperature, can be used to estimate the actual amount of moisture in the atmosphere, sometimes referred to as precipitable water. Water vapour acts as a green house gas by trapping infrared radiation reflected from the earth. This explains why desert temperatures can become much lower at night, as there is little moisture in the air to trap the heat.

Hygrometer

The best hygrometer is one which has two thermometers - one of which has its bulb wetted continuously by a wet cloth. This is called a Mason's or a 'wet-and dry-bulb' hygrometer. Air passing over this wet bulb evaporates some water and lowers the wet bulb temperature by an amount that depends on the humidity of the air. To demonstrate this cooling, wet your finger and blow in it. The humidity can be found by noting the difference in temperature between the wet and dry bulb and looking up the RH value in a set of tables. (see attached). The relative humidity (RH value) is the amount as a percentage of that required to saturate the air completely.

http://www.uswcl.ars.ag.gov/exper/relhum.htm

Measuring Pressure

Barometers are used for measuring pressure. You can make a simple barometer but a proper one is needed to make correct observations.

The simplest and cheapest is a basic aneroid barometer which has a partial vacuum in a special metal box. This expands and contracts as air pressure changes, moving a pointer around a dial. Measurements are given in millibars (mb) or in hectopascals (hPa), identical in value. You must adjust your barometer to sea-level and it is best to put it inside a screen.

Measuring Rainfall

Rain gauges are required to measure rainfall and should be located in an open area, away from anything that might cause a shadow effect. It is possible to make a simple gauge out of a 2 litre plastics drinks bottle. The instructions are given very clearly at the website

http://weblife.bangor.ac.uk/cyfrif/eng/activities/spring/rain/pupilnotes.htm

Temperature: max and min

Special Max/Min Thermometers

A special maximum and minimum thermometer actually records the highest and lowest temperatures during a particular time period, usually one day. There are two types - the liquid in glass type (known as 'Six's thermometer') has little tiny metal markers inside the tube which are pushed around by the liquid and read against a scale. The bimetallic dial type has pointers which are very easy to read. Both need to be reset after every reading.

Describe how fog forms

"Fog in a Bottle"

Fog is a cloud that forms just above the ground. It's spooky and neat. Really thick fog can reduce you to seeing only a few feet in front of you. It can be a real hazard to cars, planes and boats.

There are two kinds of fog, advection fog and radiation, or ground fog.

Advection fog is common along the pacific coast of the United States. Warm, moist air over the Pacific Ocean are blown inward. When that air moves over colder coastal waters, it cools quickly and fog forms. The fog is moved inland by the same westerly winds.

Advection fog plays an important role in the life of California Redwood trees. The Redwood trees have very shallow roots. They depend on water from sources other than water deep underground. What the trees do not get from rain, they get from the fog. Advection fog deposits moisture on the pine needles which then drips to the ground and is absorbed by the roots.

The other kind of fog is radiation, or ground fog. This fog is common lots of places. It forms when a layer of warm, moist air forms low to the ground. A layer of cooler, dry air forms overtop. As the ground cools, the warm, moist air is cooled quickly. As the air temperature lowers, small droplets of water condense, which we see as fog.

Radiation fog forms most often on cool, clear nights with a very slight breeze. It forms first in low valleys and spreads outward so long as conditions remain the same.

Make Your own Fog in a Bottle!

It's easy to simulate the formation of radiation fog. All you need are two bottles with a narrow enough neck that you can stick an ice cube into the mouth. Fill one bottle about half way with very hot water (it doesn't need to be boiling.) Fill the other bottle with about 1 inch of cold water.

After several minutes, pour out all the hot water but 1 inch. Now place an ice cube in the mouth of each bottle. Observe what happens in both bottles.

So What's Going on Here?

Why does fog form most often on autumn and winter nights?

How would a stronger breeze affect fog formation?