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L_0041 | use and conservation of resources | T_0405 | Renewable resources can be renewed as they are used. An example is timber, which comes from trees. New trees can be planted to replace those that are cut down. Sunlight is a renewable resource. It seems we will never run out of that! Just because a resource is renewable, it doesnt mean we should use it carelessly. If we arent careful, we can pollute resources. Then they may no longer be fit for use. Water is one example. If we pollute a water source it may not be usable for drinking, bathing or any other type of use. We can also overuse resources that should be renewable. In this case the resources may not be able to recover. For example, fish are renewable resources. Thats because they can reproduce and make more fish. But water pollution and overfishing can cause them to die out if their population becomes too low. Figure 20.1 shows another example. | text | null |
L_0041 | use and conservation of resources | T_0406 | Some resources cant be renewed. At least, they cant be renewed fast enough to keep up with use. Fossil fuels are examples. It takes millions of years for them to form. We are using them up much more quickly. Elements that are used to produce nuclear power are other examples. They include uranium. This element is already rare. Sooner or later, it will run out. Supplies of non-renewable resources are shrinking. This makes them harder to get. Oil is a good example. Oil reserves beneath land are running out. So oil companies have started to drill for oil far out in the ocean. This costs more money. Its also more dangerous. Figure 20.2 shows an oil rig that exploded in 2010. The explosion killed 11 people. Millions of barrels of oil spilled into the water. It took months to plug the leak. | text | null |
L_0041 | use and conservation of resources | T_0407 | Rich nations use more natural resources than poor nations. In fact, the richest 20 percent of people use 85 percent of the worlds resources. What about the poorest 20 percent of people? They use only 1 percent of the worlds resources. You can see this unequal distribution of oil resources in Figure 20.3. Imagine a world in which everybody had equal access to resources. Some people would have fewer resources than they do now. But many people would have more. In the real world, the difference between rich and poor just keeps growing. | text | null |
L_0041 | use and conservation of resources | T_0408 | Every 20 minutes, the human population adds 3,500 more people. More people need more resources. For example, we now use five times more fossil fuels than we did in 1970. The human population is expected to increase for at least 40 years. What will happen to resource use? | text | null |
L_0041 | use and conservation of resources | T_0409 | How can we protect Earths natural resources? One answer is conservation. This means saving resources. We need to save resources so some will be left for the future. We also need to protect resources from pollution and overuse. When we conserve resources, we also cut down on the trash we produce. Americans throw out 340 million tons of trash each year. We throw out 2.5 million plastic bottles alone every hour! Most of what we throw out ends up in landfills. You can see a landfill in Figure 20.4. In a landfill, all those plastic bottles take hundreds of years to break down. What are the problems caused by producing so much trash? Natural resources must be used to produce the materials. Land must be given over to dump the materials. If the materials are toxic, they may cause pollution. | text | null |
L_0041 | use and conservation of resources | T_0410 | You probably already know about the three Rs. They stand for reduce, reuse, and recycle. The third R recycle has caught on in a big way. Thats because its easy. There are thousands of places to drop off items such as aluminum cans for recycling. Many cities allow you to just put your recycling in a special can and put it at the curb. We havent done as well with the first two Rs reducing and reusing. But they arent always as easy as recycling. Recycling is better than making things from brand new materials. But it still takes some resources to turn recycled items into new ones. It takes no resources at all to reuse items or not buy them in the first place. | text | null |
L_0041 | use and conservation of resources | T_0411 | Reducing resource use means just what it says using fewer resources. There are lots of ways to reduce our use of resources. Buy durable goods. Choose items that are well made so they will last longer. Youll buy fewer items in the long run, so youll save money as well as resources. Thats a win-win! Repair rather than replace. Fix your bike rather than buying a new one. Sew on a button instead of buying a new shirt. Youll use fewer resources and save money. Buy only what you need. Dont buy a gallon of milk if you can only drink half of it before it spoils. Instead, buy a half gallon and drink all of it. You wont be wasting resources (or money!). Buy local. For example, buy local produce at a farmers market, like the one in Figure 20.5. A lot of resources are saved by not shipping goods long distances. Products bought at farmers markets use less packaging, too! About a third of what we throw out is packaging. Try to buy items with the least amount of packaging. For example, buy bulk items instead of those that are individually wrapped. Also, try to select items with packaging that can be reused or recycled. This is called precycling. Pop cans and plastic water bottles, for example, are fairly easy to recycle. Some types of packaging are harder to recycle. You can see examples in Figure 20.6. If it cant be reused or recycled, its a waste of resources. Many plastics: The recycling symbol on the bottom of plastic containers shows the type of plastic they contain. Numbers 1 and 2 are easier to recycle than higher numbers. Mixed materials: Packaging that contains more than one material may be hard to recycle. This carton is made mostly of cardboard. But it has plastic around the opening. | text | null |
L_0041 | use and conservation of resources | T_0411 | Reducing resource use means just what it says using fewer resources. There are lots of ways to reduce our use of resources. Buy durable goods. Choose items that are well made so they will last longer. Youll buy fewer items in the long run, so youll save money as well as resources. Thats a win-win! Repair rather than replace. Fix your bike rather than buying a new one. Sew on a button instead of buying a new shirt. Youll use fewer resources and save money. Buy only what you need. Dont buy a gallon of milk if you can only drink half of it before it spoils. Instead, buy a half gallon and drink all of it. You wont be wasting resources (or money!). Buy local. For example, buy local produce at a farmers market, like the one in Figure 20.5. A lot of resources are saved by not shipping goods long distances. Products bought at farmers markets use less packaging, too! About a third of what we throw out is packaging. Try to buy items with the least amount of packaging. For example, buy bulk items instead of those that are individually wrapped. Also, try to select items with packaging that can be reused or recycled. This is called precycling. Pop cans and plastic water bottles, for example, are fairly easy to recycle. Some types of packaging are harder to recycle. You can see examples in Figure 20.6. If it cant be reused or recycled, its a waste of resources. Many plastics: The recycling symbol on the bottom of plastic containers shows the type of plastic they contain. Numbers 1 and 2 are easier to recycle than higher numbers. Mixed materials: Packaging that contains more than one material may be hard to recycle. This carton is made mostly of cardboard. But it has plastic around the opening. | text | null |
L_0041 | use and conservation of resources | T_0412 | Reusing resources means using items again instead of throwing them away. A reused item can be used in the same way by someone else. Or it can be used in a new way. For example, Shana has a pair of jeans she has outgrown. She might give them to her younger sister to wear. Or she might use them to make something different for herself, say, a denim shoulder bag. Some other ideas for reusing resources are shown in Figure 20.7. | text | null |
L_0041 | use and conservation of resources | T_0413 | Many things can be recycled. The materials in them can be reused in new products. For example, plastic water bottles can be recycled. The recycled material can be made into t-shirts! Old phone books can also be recycled and made into textbooks. When you shop for new products, look for those that are made of recycled materials (see Figure 20.8). Even food scraps and lawn waste can be recycled. They can be composted and turned into humus for the garden. At most recycling centers, you can drop off metal cans, cardboard and paper products, glass containers, and plastic bottles. Recycling stations like the one in Figure 20.9 are common. Curbside recycling usually takes these items too. Do you know how to recycle in your community? Contact your local solid waste authority to find out. If you dont already recycle, start today. Its a big way you can help the planet! | text | null |
L_0042 | use and conservation of energy | T_0414 | Think about your typical day. How do you use energy? Do you take a shower when you first get out of bed? What about taking a shower uses energy? It takes energy to heat the water and to pump the water to your home. Do you eat a hot breakfast? Energy is used to cook your food. Do you ride a bus or have someone drive you to school? Motor vehicles need energy from fossil fuels to run. | text | null |
L_0042 | use and conservation of energy | T_0415 | Figure 20.10 shows the major ways energy is used in the U.S. A lot of energy is used in homes. In fact, more energy is used in homes than in stores and businesses. Even more energy is used for transportation. A lot of fuel is necessary to move people and goods around the country. Industry uses the most energy. Industrial uses account for one-third of all the energy used in the U.S. | text | null |
L_0042 | use and conservation of energy | T_0416 | Figure 20.11 shows the energy resources used in the U.S. The U.S. depends mainly on fossil fuels. Petroleum is used more than any other resource. Renewable energy resources, such as solar and wind energy, could provide all the energy we need, but they are not yet widely used in the U.S. | text | null |
L_0042 | use and conservation of energy | T_0417 | We must use energy to get energy resources. This is true of non-renewable and renewable energy. Getting fossil fuels so that they can be used takes many steps. All of these steps use energy. 1. 2. 3. 4. 5. Fossil fuels must be found. The resources must be removed from the ground. These resources need to be refined, some more than others. Fossil fuels may need to be changed to a different form of energy. Energy resources must be transported from where they are produced to where they are sold or used. Consider petroleum as an example. Oil companies explore for petroleum in areas where they think it might be. When they find it, they must determine how much is there. They must also know how hard it will be to get. If theres enough to make it worthwhile, they will decide to go for it. To extract petroleum, companies they must build huge rigs, like the one in Figure 20.12. An oil rig drills deep into the ground and pumps the oil to the surface. The oil is then transported to a refinery. At the refinery, the oil is heated. It will then separate into different products, such as gasoline and motor oil. Finally, the oil products are transported to gas stations, stores, and industries. At every step, energy is used. For every five barrels of oil we use, it takes at least one barrel to get the oil. Less energy is needed to get renewable energy sources. Solar energy is a good example. Sunlight is everywhere, so no one needs to go out and find it. We dont have to drill for it or pump it to the surface. We just need to install solar panels like the ones in Figure 20.13 and let sunlight strike them. The energy from the sunlight is changed to electricity. The electricity is used to power lights and appliances in the house. So solar energy doesnt have to be transported. | text | null |
L_0042 | use and conservation of energy | T_0418 | Nonrenewable energy resources will run out before long. Using these energy resources also produces pollution and increases global warming. For all these reasons, we need to use less of these energy sources. We also need to use them more efficiently. | text | null |
L_0042 | use and conservation of energy | T_0418 | Nonrenewable energy resources will run out before long. Using these energy resources also produces pollution and increases global warming. For all these reasons, we need to use less of these energy sources. We also need to use them more efficiently. | text | null |
L_0042 | use and conservation of energy | T_0418 | Nonrenewable energy resources will run out before long. Using these energy resources also produces pollution and increases global warming. For all these reasons, we need to use less of these energy sources. We also need to use them more efficiently. | text | null |
L_0042 | use and conservation of energy | T_0419 | There are many ways to use less energy. Table 20.2 lists some of them. Can you think of other ways to use less energy? For example, how might schools use less energy? Use of Energy Transportation How to Use Less Plan ahead to reduce the number of trips you make. Take a bus or train instead of driving. Walk or bike rather than ride. Home Unplug appliances when not in use. Turn off lights when you leave a room. Put on a sweater instead of turning up the heat. Run the dishwasher and washing machine only when full. | text | null |
L_0042 | use and conservation of energy | T_0420 | We can get more work out of the energy we use. Table 20.3 show some ways to use energy more efficiently. By getting more bang for the buck, we wont need to use as much energy overall. Does your family use energy efficiently? How could you find out? Use of Energy More Efficient Use Another way to use energy more efficiently is with Energy Star appliances. They carry the Energy Star logo, shown in Figure 20.14. To be certified as Energy Star, the appliance must use less energy. Energy Star appliances save a lot of energy over their lifetime. What if millions of households used Energy Star appliances? How much energy would it save? | text | null |
L_0043 | humans and the water supply | T_0421 | Figure 21.1 shows how people use water worldwide. The greatest use is for agriculture and then industry. Municipal use is last, but is also important. Municipal use refers to water used by homes and businesses in communities. | text | null |
L_0043 | humans and the water supply | T_0422 | Many crops are grown where there isnt enough rainfall for plants to thrive. For example, crops are grown in deserts of the American southwest. How is this possible? The answer is irrigation. Irrigation is any way of providing extra water to plants. Most of the water used in agriculture is used for irrigation. Livestock also use water, but they use much less. Irrigation can waste a lot of water. The type of irrigation shown in Figure 21.2 is the most wasteful. The water is sprayed into the air and then falls to the ground. But much of the water never reaches the crops. Instead, it evaporates in the air or runs off the fields. Irrigation water may cause other problems. The water may dissolve agricultural chemicals such as pesticides. When the water soaks into the ground, the dissolved chemicals do, too. They may enter groundwater or run off into rivers or lakes. Salts in irrigation water can also collect in the soil. The soil may get too salty for plants to grow. | text | null |
L_0043 | humans and the water supply | T_0422 | Many crops are grown where there isnt enough rainfall for plants to thrive. For example, crops are grown in deserts of the American southwest. How is this possible? The answer is irrigation. Irrigation is any way of providing extra water to plants. Most of the water used in agriculture is used for irrigation. Livestock also use water, but they use much less. Irrigation can waste a lot of water. The type of irrigation shown in Figure 21.2 is the most wasteful. The water is sprayed into the air and then falls to the ground. But much of the water never reaches the crops. Instead, it evaporates in the air or runs off the fields. Irrigation water may cause other problems. The water may dissolve agricultural chemicals such as pesticides. When the water soaks into the ground, the dissolved chemicals do, too. They may enter groundwater or run off into rivers or lakes. Salts in irrigation water can also collect in the soil. The soil may get too salty for plants to grow. | text | null |
L_0043 | humans and the water supply | T_0423 | Almost a quarter of the water used worldwide is used in industry. Industries use water for many purposes. Chemical processes need a lot of water. Water is used to generate electricity. An important way that industries use water is to cool machines and power plants. | text | null |
L_0043 | humans and the water supply | T_0424 | Think about all the ways people use water at home. Besides drinking it, they use it for cooking, bathing, washing dishes, doing laundry, and flushing toilets. The water used inside homes goes down the drain. From there it usually ends up in a sewer system. At the sewage treatment plant, water can be is treated and prepared for reuse. Households may also use water outdoors. If your family has a lawn or garden, you may water them with a hose or sprinkler. You probably use water to wash the car, like the teen in Figure 21.3. Much of the water used outdoors evaporates or runs off into the gutter. The runoff water may end up in storm sewers that flow into a body of water, such as the ocean. | text | null |
L_0043 | humans and the water supply | T_0425 | There are many ways to use water for fun, from white water rafting to snorkeling. When you do these activities you dont actually use water. You are doing the activity on or in the water. What do you think is the single biggest use of water for fun? Believe it or not, its golf! Keeping golf courses green uses an incredible amount of water. Since many golf courses are in sunny areas, much of the water is irrigation water. Many golf courses, like the one in Figure 21.4, have sprinkler systems. Like any similar sprinkler system, much of this water is wasted. It evaporates or runs off the ground. | text | null |
L_0043 | humans and the water supply | T_0426 | Most Americans have plenty of fresh, clean water. But many people around the world do not. In fact, water scarcity is the worlds most serious resource problem. How can that be? Water is almost everywhere. More than 70 percent of Earths surface is covered by water. | text | null |
L_0043 | humans and the water supply | T_0427 | One problem is that only a tiny fraction of Earths water is fresh, liquid water that people can use. More than 97 percent of Earths water is salt water in the oceans. Just 3 percent is freshwater. Most of the freshwater is frozen in ice sheets, icebergs, and glaciers (see Figure 21.5). | text | null |
L_0043 | humans and the water supply | T_0428 | Rainfall varies around the globe. About 40 percent of the land gets very little rain. About the same percentage of the worlds people dont have enough water. You can compare global rainfall with the worldwide freshwater supply at the two URLs below. Drier climates generally have less water for people to use. In some places, people may have less water available to them for an entire year than many Americans use in a single day! How much water is there where you live? Global rainfall: http://commons.wikimedia.org/wiki/File:World_precip_annual.png Freshwater supply: http://commons.wikimedia.org/wiki/File:2006_Global_Water_Availability.svg | text | null |
L_0043 | humans and the water supply | T_0429 | Richer nations can drill deep wells, build large dams or supply people with water in other ways. In these countries, just about everyone has access to clean running water in their homes. Its no surprise that people in these countries also use the most water. In poorer nations, there is little money to develop water supplies. Look at the people in Figure 21.6. These people must carry water home in a bucket from a distant pump. | text | null |
L_0043 | humans and the water supply | T_0430 | Water shortages are common in much of the world. People are most likely to run short of water during droughts. A drought is a period of unusually low rainfall. Human actions have increased how often droughts occur. One way people can help to bring on drought is by cutting down trees. Trees add a lot of water vapor to the air. With fewer trees, the air is drier and droughts are more common. We already use six times as much water today as we did a hundred years ago. As the number of people rises, our need for water will grow. By the year 2025, only half the worlds people will have enough clean water. Water is such a vital resource that serious water shortages may cause other problems. Crops and livestock may die, so people will have less food available. Other uses of water, such as industry, may have to stop. This reduces the jobs people can get and the products they can buy. People and nations may fight over water resources. In extreme cases, people may die from lack of water. The Figure 21.7 shows the global water situation in the 2030s with water stress and water scarcity on the map. | text | null |
L_0043 | humans and the water supply | T_0431 | The water Americans get from their faucets is generally safe. This water has been treated and purified. But at least 20 percent of the worlds people do not have clean drinking water. Their only choice may be to drink water straight from a river (see Figure 21.8). If the river is polluted with wastes, it will contain bacteria and other organisms that cause disease. Almost 9 out of 10 cases of disease worldwide are caused by unsafe drinking water. Diseases from unsafe drinking water are the leading cause of death in young children. | text | null |
L_0044 | water pollution | T_0432 | Pollution that enters water at just one point is called point source pollution. For example, chemicals from a factory might empty into a stream through a pipe or set of pipes (see Figure 21.9). Pollution that enters in many places is called non-point source pollution. This means that the pollution is from multiple sources. With non-point source pollution, runoff may carry the pollution into a body of water. Which type of pollution do you think is harder to control? | text | null |
L_0044 | water pollution | T_0433 | There are three main sources of water pollution: 1. Agriculture. 2. Industry. 3. Municipal, or community, sources. | text | null |
L_0044 | water pollution | T_0434 | Huge amounts of chemicals, such as fertilizers and pesticides, are applied to farm fields (see Figure 21.10). Some of the chemicals are picked up by rainwater. Runoff then carries the chemicals to nearby rivers or lakes. Dissolved fertilizer causes too much growth of water plants and algae. This can lead to dead zones where nothing can live in lakes and at the mouths of rivers. Some of the chemicals can infiltrate into groundwater. The contaminated water comes up in water wells. If people drink the polluted water, they may get sick. Waste from livestock can also pollute water. The waste contains bacteria and other organisms that cause disease. In fact, more than 40 human diseases can be caused by water polluted with animal waste. Many farms in the U.S. have thousands of animals. These farms produce millions of gallons of waste. The waste is stored in huge lagoons, like the one in Figure 21.11. Unfortunately, many leaks from these lagoons have occurred. Two examples are described below. In North Carolina, 25 million gallons of hog manure spilled into a nearby river. The contaminated water killed | text | null |
L_0044 | water pollution | T_0434 | Huge amounts of chemicals, such as fertilizers and pesticides, are applied to farm fields (see Figure 21.10). Some of the chemicals are picked up by rainwater. Runoff then carries the chemicals to nearby rivers or lakes. Dissolved fertilizer causes too much growth of water plants and algae. This can lead to dead zones where nothing can live in lakes and at the mouths of rivers. Some of the chemicals can infiltrate into groundwater. The contaminated water comes up in water wells. If people drink the polluted water, they may get sick. Waste from livestock can also pollute water. The waste contains bacteria and other organisms that cause disease. In fact, more than 40 human diseases can be caused by water polluted with animal waste. Many farms in the U.S. have thousands of animals. These farms produce millions of gallons of waste. The waste is stored in huge lagoons, like the one in Figure 21.11. Unfortunately, many leaks from these lagoons have occurred. Two examples are described below. In North Carolina, 25 million gallons of hog manure spilled into a nearby river. The contaminated water killed | text | null |
L_0044 | water pollution | T_0435 | Factories and power plants may pollute water with harmful substances. Many industries produce toxic chemicals. Some of the worst are arsenic, lead, and mercury. Nuclear power plants produce radioactive chemicals. They cause cancer and other serious health problems. Oil tanks and pipelines can leak. Leaks may not be noticed until a lot of oil has soaked into the ground. The oil may pollute groundwater so it is no longer fit to drink. | text | null |
L_0044 | water pollution | T_0436 | Municipal refers to the community. Households and businesses in a community are also responsible for polluting the water supply. For example: People apply chemicals to their lawns. The chemicals may be picked up by rainwater. The contaminated runoff enters storm sewers and ends up in nearby rivers or lakes. Underground septic tanks can develop leaks. This lets household sewage seep into groundwater. Municipal sewage treatment plants dump treated wastewater into rivers or lakes. Sometimes the wastewater is not treated enough and contains bacteria or toxic chemicals. | text | null |
L_0044 | water pollution | T_0437 | The oceans are vast. You might think they are too big to be harmed by pollution. But thats not the case. Ocean water is becoming seriously polluted. | text | null |
L_0044 | water pollution | T_0438 | The oceans are most polluted along coasts. Why do you think thats the case? Of course, its because most pollution enters the oceans from the land. Runoff and rivers carry the majority of pollution into the ocean. Many cities dump their wastewater directly into coastal waters. In some parts of the world, raw sewage and trash may be thrown into the water (see Figure 21.12). Coastal water may become so polluted that people get sick if they swim in it or eat seafood from it. The polluted water may also kill fish and other ocean life. | text | null |
L_0044 | water pollution | T_0439 | Oil spills are another source of ocean pollution. To get at oil buried beneath the seafloor, oil rigs are built in the oceans. These rigs pump oil from beneath the ocean floor. Huge ocean tankers carry oil around the world. If something goes wrong with a rig on a tanker, millions of barrels of oil may end up in the water. The oil may coat and kill ocean animals. Some of the oil will wash ashore. This oil may destroy coastal wetlands and ruin beaches. Figure 21.13 shows an oil spill on a beach. The oil washed ashore after a deadly oil rig explosion in the Gulf of Mexico in 2010. | text | null |
L_0044 | water pollution | T_0440 | Thermal pollution is pollution that raises the temperature of water. This is caused by power plants and factories that use the water to cool their machines. The plants pump cold water from a lake or coastal area through giant cooling towers, like those in Figure 21.14. As it flows through the towers, the cold water absorbs heat. This warmed water is returned to the lake or sea. Thermal pollution can kill fish and other water life. Its not just the warm temperature that kills them. Warm water cant hold as much oxygen as cool water. If the water gets too warm, there may not be enough oxygen for living things. | text | null |
L_0045 | protecting the water supply | T_0441 | In the mid 1900s, people were startled to see the Cuyahoga River in Cleveland, Ohio, burst into flames! The river was so polluted with oil and other industrial wastes that it was flammable. Nothing could live in it. You can see the Cuyahoga River in Figure 21.16 | text | null |
L_0045 | protecting the water supply | T_0442 | Disasters such as rivers burning led to new U.S. laws to protect the water. For example, the Environmental Protection Agency (EPA) was established, and the Clean Water Act was passed. Now, water is routinely tested. Pollution is tracked to its source, and polluters are forced to fix the problem and clean up the pollution. They are also fined. These consequences have led industries, agriculture, and communities to pollute the water much less than before. | text | null |
L_0045 | protecting the water supply | T_0443 | Most water pollution comes from industry, agriculture, and municipal sources. Homes are part of the municipal source and the individuals and families that live in them can pollute the water supply. What can you do to reduce water pollution? Read the tips below. Properly dispose of motor oil and household chemicals. Never pour them down the drain. Also, dont let them spill on the ground. This keeps them out of storm sewers and bodies of water. Use fewer lawn and garden chemicals. Use natural products instead. For example, use compost instead of fertilizer. Or grow plants that can thrive on their own without any extra help. Repair engine oil leaks right away. A steady drip of oil from an engine can quickly add up to gallons. When the oil washes off driveways and streets it can end up in storm drains and pollute the water supply. Dont let pet litter or pet wastes get into the water supply (see Figure 21.17). The nitrogen they contain can cause overgrowth of algae. The wastes may also contain bacteria and other causes of disease. | text | null |
L_0045 | protecting the water supply | T_0444 | Water treatment is a series of processes that remove unwanted substances from water. The goal of water treatment is to make the water safe to return to the natural environment or to the human water supply. Treating water for other purposes may not include all the same steps. Thats because water used in agriculture or industry may not have to be as clean as drinking water. You can see how water for drinking is treated in Figure 21.18. Treating drinking water requires at least four processes: 1. Chemicals are added to untreated water. They cause solids in the water to clump together. This is called coagulation. 2. The water is moved to tanks. The clumped solids sink to the bottom of the water. This is called sedimentation. 3. The water is passed through filters that remove smaller particles from the water. This is called filtration. 4. Chlorine is added to the water to kill bacteria and other microbes. This is called disinfection. Finally, the water is pure enough to drink. | text | null |
L_0045 | protecting the water supply | T_0445 | Conserving water means using less of it. Of course, this mostly applies to people in the wealthy nations that have the most water and also waste the most. | text | null |
L_0045 | protecting the water supply | T_0446 | Irrigation is the single biggest use of water. Overhead irrigation wastes a lot of water. Drip irrigation wastes a lot less. Figure 21.19 shows a drip irrigation system. Water pipes run over the surface of the ground. Tiny holes in the pipes are placed close to each plant. Water slowly drips out of the holes and soaks into the soil around the plants. Very little of the water evaporates or runs off the ground. | text | null |
L_0045 | protecting the water supply | T_0447 | Some communities save water with rationing. Much rationing takes place only during times of drought. During rationing, water may not be used for certain things. For example, communities may ban lawn watering and car washing. People may be fined if they use water in these ways. You can do your part. Follow any bans where you live. | text | null |
L_0045 | protecting the water supply | T_0448 | Its easy to save water at home. If you save even a few gallons a day you can make a big difference over the long run. The best place to start saving water is in the bathroom. Toilet flushing is the single biggest use of water in the home. Showers and baths are the next biggest use. Follow the tips below to save water at home. Install water-saving toilets. They use only about half as much water per flush. A single household can save up to 20,000 gallons a year with this change alone! Take shorter showers. You can get just as clean in 5 minutes as you can in 10. And youll save up to 50 gallons of water each time you shower. Thats thousands of gallons each year. Use low-flow shower heads. They use about half as much water as regular shower heads. They save thousands of gallons of water. Fix leaky shower heads and faucets. All those drips really add up. At one drip per second, more than 6,000 gallons go down the drain in a year per faucet! Dont leave the water running while you brush your teeth. You could save as much as 10 gallons each time you brush. That could add up to 10,000 gallons in a year. Landscape your home with plants that need little water. This could result in a huge savings in water use. Look at the garden in Figure 21.20. It shows that you dont have to sacrifice beauty to save water. | text | null |
L_0047 | air pollution | T_0452 | Air quality is a measure of the pollutants in the air. More pollutants mean poorer air quality. Air quality, in turn, depends on many factors. Some natural processes add pollutants to the air. For example, forest fires and volcanoes add carbon dioxide and soot. In dry areas, the air often contains dust. However, human actions cause the most air pollution. The single biggest cause is fossil fuel burning. | text | null |
L_0047 | air pollution | T_0453 | Poor air quality started to become a serious problem after the Industrial Revolution. The machines in factories burned coal. This released a lot of pollutants into the air. After 1900, motor vehicles became common. Cars and trucks burn gasoline, which adds greatly to air pollution. | text | null |
L_0047 | air pollution | T_0454 | By the mid-1900s, air quality in many big cities was very bad. The worst incident came in December 1952. A temperature inversion over London, England, kept cold air and pollutants near the ground. The air became so polluted that thousands of people died in just a few days. This event was called the Big Smoke. | text | null |
L_0047 | air pollution | T_0455 | At the same time, many U.S. cities had air pollution problems. Some of the worst were in California. Cars were becoming more popular. Oil refineries and power plants also polluted the air. Mountain ranges trapped polluted air over cities. The California sunshine caused chemical reactions among the pollutants. These reactions produced many more harmful compounds. | text | null |
L_0047 | air pollution | T_0456 | By 1970, it was clear that something needed to be done to protect air quality. In the U.S., the Clean Air Act was passed. It limits what can be released into the air. As a result, the air in the U.S. is much cleaner now than it was 50 years ago. But air pollution has not gone away. Vehicles, factories, and power plants still release more than 150 million tons of pollutants into the air each year. | text | null |
L_0047 | air pollution | T_0457 | There are two basic types of pollutants in air. They are known as primary pollutants and secondary pollutants. | text | null |
L_0047 | air pollution | T_0458 | Primary pollutants enter the air directly. Some are released by natural processes, like ash from volcanoes. Most are released by human activities. They pour into the air from vehicles and smokestacks. Several of these pollutants are described below. Carbon oxides include carbon monoxide (CO) and carbon dioxide (CO2 ). Carbon oxides are released when fossil fuels burn. Nitrogen oxides include nitric oxide (NO) and nitrogen dioxide (NO2 ). Nitrogen oxides form when nitrogen and oxygen combine at high temperatures. This occurs in hot exhausts from vehicles, factories, and power plants. Sulfur oxides include sulfur dioxide (SO2 ) and sulfur trioxide (SO3 ). Sulfur oxides are produced when sulfur and oxygen combine. This happens when coal burns. Coal can contain up to 10 percent sulfur. Toxic heavy metals include mercury and lead. Mercury is used in some industrial processes. It is also found in fluorescent light bulbs. Lead was once widely used in gasoline, paint, and pipes. It is still found in some products. Volatile organic compounds (VOCs) are carbon compounds such as methane. VOCs are released in many human activities, such as raising livestock. Livestock wastes produce a lot of methane. Particulates are solid particles. These particles may be ash, dust, or even animal wastes. Many are released when fossil fuels burn (see Figure 22.1). | text | null |
L_0047 | air pollution | T_0459 | Secondary pollutants form when primary pollutants undergo chemical reactions after they are released. Many occur as part of photochemical smog. This type of smog is seen as a brown haze in the air. Photochemical smog forms when certain pollutants react together in the presence of sunlight. You can see smog hanging in the air over San Francisco in Figure 22.2. Photochemical smog consists mainly of ozone (O3 ). The ozone in smog is the same compound as the ozone in the ozone layer,(O3 ). But ozone in smog is found near the ground. Figure 22.3 shows how it forms. When nitrogen oxides and VOCs are heated by the Sun, they lose oxygen atoms. The oxygen atoms combine with molecules of oxygen to form ozone. Smog ozone is harmful to humans and other living things. | text | null |
L_0047 | air pollution | T_0460 | Most pollutants enter the air when fossil fuels burn. Some are released when forests burn. Others evaporate into the air. | text | null |
L_0047 | air pollution | T_0461 | Burning fossil fuels releases many pollutants into the air. These pollutants include carbon monoxide, carbon dioxide, nitrogen dioxide, and sulfur dioxide. Motor vehicles account for almost half of fossil fuel use. Most vehicles run on gasoline, which comes from petroleum. Power plants and factories account for more than a quarter of fossil fuel use. Power plants burn fossil fuels to generate electricity. Factories burn fossil fuels to power machines. Homes and other buildings also burn fossil fuels. The energy they release is used for heating, cooking, and other purposes. | text | null |
L_0047 | air pollution | T_0462 | Millions of acres of forest have been cut and burned to make way for farming. Figure 22.4 shows an example. Burning trees produces most of the same pollutants as burning fossil fuels. | text | null |
L_0047 | air pollution | T_0463 | VOCs enter the air by evaporation. VOCs are found in many products, like paints and petroleum products. Methane is a VOC that evaporates from livestock waste and landfills. | text | null |
L_0048 | effects of air pollution | T_0464 | All air pollutants are harmful. Thats why theyre called pollutants. Some air pollutants damage the environment as well as the health of living things. The type of damage depends on the pollutant. | text | null |
L_0048 | effects of air pollution | T_0465 | Particulates cause lung diseases. They can also increase the risk of heart disease and the number of asthma attacks. Particulates block sunlight from reaching Earths surface. This means there is less energy for photosynthesis. Less photosynthesis means that plants and phytoplankton produce less food. This affects whole ecosystems. | text | null |
L_0048 | effects of air pollution | T_0466 | The ozone in smog may damage plants. The effects of ozone add up over time. Plants such as trees, which normally live a long time, are most affected. Entire forests may die out if ozone levels are very high. Other plants, including crop plants, may also be damaged by ozone. You can see evidence of ozone damage in Figure 22.5. The ozone in smog is also harmful to human health. Figure 22.6 shows the levels of ozone to watch out for. Some people are especially sensitive to ozone. They can be harmed by levels of ozone that would not affect most other people. These people include those with lung or heart problems. | text | null |
L_0048 | effects of air pollution | T_0466 | The ozone in smog may damage plants. The effects of ozone add up over time. Plants such as trees, which normally live a long time, are most affected. Entire forests may die out if ozone levels are very high. Other plants, including crop plants, may also be damaged by ozone. You can see evidence of ozone damage in Figure 22.5. The ozone in smog is also harmful to human health. Figure 22.6 shows the levels of ozone to watch out for. Some people are especially sensitive to ozone. They can be harmed by levels of ozone that would not affect most other people. These people include those with lung or heart problems. | text | null |
L_0048 | effects of air pollution | T_0467 | Both nitrogen and sulfur oxides are toxic to humans. These compounds can cause lung diseases or make them worse. Nitrogen and sulfur oxides form acid rain, which is described below. | text | null |
L_0048 | effects of air pollution | T_0468 | Carbon monoxide (CO) is toxic to both plants and animals. CO is deadly to people in a confined space, such as a closed home. Carbon monoxide is odorless and colorless, so people cant tell when they are breathing it. Thats why homes should have carbon monoxide detectors. You can see one in Figure 22.7. | text | null |
L_0048 | effects of air pollution | T_0469 | Heavy metals, such as mercury and lead, are toxic to living things. They can enter food chains from the atmosphere. The metals build up in the tissues of organisms by bioaccumulation. Bioaccumulation is illustrated in Figure 22.8. As heavy metals are passed up a food chain they accumulate. Imagine a low-level consumer eating a producer. That consumer takes in all of the heavy metals from all of the producers that it eats. Then a higher-level consumer eats it and accumulates all the heavy metals from all of the lower-level consumers that it eats. In this way, heavy metals may accumulate. At high levels in the food chain, the heavy metals may be quite become quite concentrated. The higher up a food chain that humans eat, the greater the levels of toxic metals they take in. Thats why people should avoid eating too much of large fish such as tuna. Tuna are predators near the top of their food chains. They have been shown to contain high levels of mercury. In people, heavy metals can damage the brain and other organs. Unborn babies and young children are most affected. Thats because their organs are still developing. | text | null |
L_0048 | effects of air pollution | T_0469 | Heavy metals, such as mercury and lead, are toxic to living things. They can enter food chains from the atmosphere. The metals build up in the tissues of organisms by bioaccumulation. Bioaccumulation is illustrated in Figure 22.8. As heavy metals are passed up a food chain they accumulate. Imagine a low-level consumer eating a producer. That consumer takes in all of the heavy metals from all of the producers that it eats. Then a higher-level consumer eats it and accumulates all the heavy metals from all of the lower-level consumers that it eats. In this way, heavy metals may accumulate. At high levels in the food chain, the heavy metals may be quite become quite concentrated. The higher up a food chain that humans eat, the greater the levels of toxic metals they take in. Thats why people should avoid eating too much of large fish such as tuna. Tuna are predators near the top of their food chains. They have been shown to contain high levels of mercury. In people, heavy metals can damage the brain and other organs. Unborn babies and young children are most affected. Thats because their organs are still developing. | text | null |
L_0048 | effects of air pollution | T_0470 | VOCs are toxic to humans and other living things. In people, they can cause a wide range of problems, from eye and nose irritation to brain damage and cancer. Levels of VOCs are often higher indoors than out. Thats because they are released by products such as paints, cleaning solutions, and building materials. How might you reduce your exposure to VOCs? | text | null |
L_0048 | effects of air pollution | T_0471 | Acid rain is rain that has a pH less than 5 (see Figure 22.9). The pH of normal rain is 5.6. Its slightly acidic because carbon dioxide in the air dissolves in rain. This forms carbonic acid, a weak acid. | text | null |
L_0048 | effects of air pollution | T_0472 | Acid rain forms when nitrogen and sulfur oxides in air dissolve in rain (see Figure 22.10). This forms nitric and sulfuric acids. Both are strong acids. Acid rain with a pH as low as 4.0 is now common in many areas. Acid fog may be even more acidic than acid rain. Fog with a pH as low as 1.7 has been recorded. Thats the same pH as toilet bowl cleaner! | text | null |
L_0048 | effects of air pollution | T_0473 | Figure 22.11 shows some of the damage done by acid rain. Acid rain ends up in soil and bodies of water. This can make them very acidic. The acid strips soil of its nutrients. These changes can kill trees, fish, and other living things. Acid rain also dissolves limestone and marble. This can damage buildings, monuments, and statues. | text | null |
L_0048 | effects of air pollution | T_0474 | Ozone near the ground harms human health. But the ozone layer in the stratosphere protects us from solar rays. Thats why people were alarmed in the 1980s to learn that there was a hole in the ozone layer. | text | null |
L_0048 | effects of air pollution | T_0475 | Whats destroying the ozone layer? The chief cause is chlorofluorocarbons (CFCs). These are human-made chemicals that contain the element chlorine (Cl). In the past, CFCs were widely used in spray cans, refrigerators, and many other products. CFCs are stable compounds that can remain in the atmosphere for hundreds of years. Once CFCs are in the air, they float up into the stratosphere. What happens next is shown in Figure 22.12. Sunlight breaks apart the molecules. This releases their chlorine atoms (Cl). The free chlorine atoms may then combine with oxygen atoms in ozone. This breaks down the ozone molecules into an oxygen molecule and an oxygen atom. One CFC molecule can break down as many as 100,000 ozone molecules in this way! These forms of oxygen do not protect the planet from ultraviolet radiation. | text | null |
L_0048 | effects of air pollution | T_0476 | Most ozone loss it taking place over the South Pole and Antarctica. This is the location of the ozone hole. The ozone hole is also seasonal. The hole forms during the early part spring in the Southern Hemisphere and then grows northward. You can see the hole in Figure 22.13. Besides the ozone hole, the ozone layer is thinner over the Northern Hemisphere. | text | null |
L_0048 | effects of air pollution | T_0476 | Most ozone loss it taking place over the South Pole and Antarctica. This is the location of the ozone hole. The ozone hole is also seasonal. The hole forms during the early part spring in the Southern Hemisphere and then grows northward. You can see the hole in Figure 22.13. Besides the ozone hole, the ozone layer is thinner over the Northern Hemisphere. | text | null |
L_0048 | effects of air pollution | T_0477 | With less ozone in the stratosphere, more UV rays reach the ground. More UV rays increase skin cancer rates. Just a 1 percent loss of ozone causes a 5 percent increase in skin cancer. More UV rays also harm plants and phytoplankton. As a result, they produce less food. This may affect entire ecosystems. | text | null |
L_0049 | reducing air pollution | T_0478 | There are two basic types of strategies for reducing pollution from fossil fuels: 1. Use less fossil fuel to begin with. 2. When fossil fuels must be used, prevent the pollution from entering the air. | text | null |
L_0049 | reducing air pollution | T_0479 | We can reduce our use of fossil fuels in several ways: Conserve fossil fuels. For example, turning out lights when we arent using them saves electricity. Why does this help? A lot of the electricity we use comes from coal-burning power plants. Use fossil fuels more efficiently. For example, driving a fuel-efficient car lets you go farther on each gallon of gas. This can add up to a big savings in fossil fuel use. Change to alternative energy sources that produce little or no air pollution. For example, hybrid cars run on electricity that would be wasted during braking. These cars use gas only as a backup fuel. As a result, they produce just 10 percent of the air pollution produced by cars that run only on gas. Cars that run on hydrogen and produce no pollution at all have also been developed (see Figure 22.14). | text | null |
L_0049 | reducing air pollution | T_0480 | Some of the pollutants from fossil fuels can be filtered out of exhaust before it is released into the air. Other pollutants can be changed to harmless compounds before they are released. Two widely used technologies are scrubbers and catalytic converters. Scrubbers are used in factories and power plants. They remove particulates and waste gases from exhaust before it is released to the air. You can see how a scrubber works in Figure 22.15. Catalytic converters are used on motor vehicles. They break down pollutants in exhaust to non-toxic com- pounds. For example, they change nitrogen oxides to harmless nitrogen and oxygen gasses. | text | null |
L_0049 | reducing air pollution | T_0481 | The problems of ozone loss and global warming were unknown in 1970. When they were discovered, worldwide efforts were made to reduce CFCs and carbon dioxide emissions. | text | null |
L_0049 | reducing air pollution | T_0482 | The Montreal Protocol is a worldwide agreement on air pollution. It focuses on CFCs. It was signed by many countries in 1987. It controls almost 100 chemicals that can damage the ozone layer. Its aim is to return the ozone layer to its normal state. The Montreal Protocol has been effective in controlling CFCs. By 1995, few CFCs were still being used. But the ozone hole kept growing for several years after that because of the CFCs already in the atmosphere. It peaked in 2006. Since then, it has been somewhat smaller. | text | null |
L_0049 | reducing air pollution | T_0483 | The Kyoto Protocol is another worldwide agreement on air pollution. It was passed in 1997. The Protocol focuses on controlling greenhouse gas emissions. Its aim is to control global warming. Carbon dioxide is the main greenhouse gas causing global warming. There are several possible ways to reduce carbon dioxide emissions. They include cap-and-trade systems, carbon taxes, and carbon sequestration In a cap-and-trade system, each nation is given a cap, or upper limit, on carbon dioxide emissions. If a nation needs to go over its cap, it can trade with another nation that is below its cap. Figure 22.16 shows how this works. Carbon taxes are taxes placed on gasoline and other products that produce carbon dioxide. The taxes encourage people to use less fossil fuel, which reduces carbon dioxide emissions. Carbon sequestration is any way of removing carbon dioxide from the atmosphere and storing it in another form. Carbon is sequestered naturally by forests. Trees take in carbon dioxide for photosynthesis. Artificial methods of sequestering carbon underground are being researched. The Kyoto Protocol has not been as successful as the Montreal Protocol. One reason is that the worlds biggest producer of greenhouse gases, the U.S., did not sign the Kyoto Protocol. Of the nations that signed it, few are | text | null |
L_0050 | telescopes | T_0484 | Earth is just a tiny speck in the universe. Our planet is surrounded by lots of space. Light travels across empty space. Astronomers can study light from stars to learn about the universe. Light is the visible part of the electromagnetic spectrum. Astronomers use the light that comes to us to gather information about the universe. | text | null |
L_0050 | telescopes | T_0485 | In space, light travels at about 300,000,000 meters per second (670,000,000 miles per hour). How fast is that? A beam of light could travel from New York to Los Angeles and back again nearly 40 times in just one second. Even at that amazing rate, objects in space are so far away that it takes a lot of time for their light to reach us. Even light from the nearest star, our Sun, takes about 8 minutes to reach Earth. | text | null |
L_0050 | telescopes | T_0486 | We need a really big unit to measure distances out in space because distances between stars are so great. A light- year, 9.5 trillion kilometers (5.9 trillion miles), is the distance that light travels in one year. Thats a long way! Out in space, its actually a pretty short distance. Proxima Centauri is the closest star to us after the Sun. This near neighbor is 4.22 light-years away. That means the light from Proxima Centauri takes 4.22 years to reach us. Our galaxy, the Milky Way Galaxy, is about 100,000 light-years across. So it takes light 100,000 years to travel from one side of the galaxy to the other! It turns out that even 100,000 light years is a short distance. The most distant galaxies we have detected are more than 13 billion light-years away. Thats over a hundred-billion-trillion kilometers! | text | null |
L_0050 | telescopes | T_0487 | When we look at stars and galaxies, we are seeing over great distances. More importantly, we are also seeing back in time. When we see a distant galaxy, we are actually seeing how the galaxy used to look. For example, the Andromeda Galaxy, shown in Figure 23.1, is about 2.5 million light-years from Earth. When you see an image of the galaxy what are you seeing? You are seeing the galaxy as it was 2.5 million years ago! Since scientists can look back in time they can better understand the Universes history. Check out http://science.n | text | null |
L_0050 | telescopes | T_0488 | Light is one type of electromagnetic radiation. Light is energy that travels in the form of an electromagnetic wave. Figure 23.2 shows a diagram of an electromagnetic wave. An electromagnetic (EM) wave has two parts: an electric field and a magnetic field. The electric and magnetic fields vibrate up and down, which makes the wave. The wavelength is the horizontal distance between two of the same points on the wave, like wave crest to wave crest. A waves frequency measures the number of wavelengths that pass a given point every second. As wavelength increases, frequency decreases. This means that as wavelengths get shorter, more waves move past a particular spot in the same amount of time. | text | null |
L_0050 | telescopes | T_0488 | Light is one type of electromagnetic radiation. Light is energy that travels in the form of an electromagnetic wave. Figure 23.2 shows a diagram of an electromagnetic wave. An electromagnetic (EM) wave has two parts: an electric field and a magnetic field. The electric and magnetic fields vibrate up and down, which makes the wave. The wavelength is the horizontal distance between two of the same points on the wave, like wave crest to wave crest. A waves frequency measures the number of wavelengths that pass a given point every second. As wavelength increases, frequency decreases. This means that as wavelengths get shorter, more waves move past a particular spot in the same amount of time. | text | null |
L_0050 | telescopes | T_0489 | Visible light is the part of the electromagnetic spectrum (Figure 23.3) that humans can see. Visible light includes all the colors of the rainbow. Each color is determined by its wavelength. Visible light ranges from violet wavelengths of 400 nanometers (nm) through red at 700 nm. There are parts of the electromagnetic spectrum that humans cannot see. This radiation exists all around you. You just cant see it! Every star, including our Sun, emits radiation of many wavelengths. Astronomers can learn a lot from studying the details of the spectrum of radiation from a star. Many extremely interesting objects cant be seen with the unaided eye. Astronomers use telescopes to see objects at wavelengths all across the electromagnetic spectrum. Some very hot stars emit light primarily at ultraviolet wavelengths. There are extremely hot objects that emit X-rays and even gamma rays. Some very cool stars shine mostly in the infrared light wavelengths. Radio waves come from the faintest, most distant objects. To learn more about stars spectra, visit | text | null |
L_0050 | telescopes | T_0490 | null | text | null |
L_0050 | telescopes | T_0491 | Humans have been making and using magnifying lenses for thousands of years. The first telescope was built by Galileo in 1608. His telescope used two lenses to make distant objects appear both nearer and larger. Telescopes that use lenses to bend light are called refracting telescopes, or refractors (Figure 23.4). The earliest telescopes were all refractors. Many amateur astronomers still use refractors today. Refractors are good for viewing details within our solar system. Craters on the surface of Earths Moon or the rings around Saturn are two such details. Around 1670, Sir Isaac Newton built a different kind of telescope. Newtons telescope used curved mirrors instead of lenses to focus light. This type of telescope is called a reflecting telescope, or reflector (see Figure 23.5). The mirrors in a reflecting telescope are much lighter than the heavy glass lenses in a refractor. This is important because a refracting telescope must be much stronger to support the heavy glass. Its much easier to precisely make mirrors than to precisely make glass lenses. For that reason, reflectors can be made larger than refractors. Larger telescopes can collect more light. This means that they can study dimmer or more distant objects. The largest optical telescopes in the world today are reflectors. Telescopes can also be made to use both lenses and mirrors. For more on how telescopes were developed, visit http://galileo.rice.edu/sci/instruments/telescope.html . | text | null |
L_0050 | telescopes | T_0492 | Radio telescopes collect radio waves. These telescopes are even larger telescopes than reflectors. Radio telescopes look a lot like satellite dishes. In fact, both are designed to collect and focus radio waves or microwaves from space. The largest single radio telescope in the world is at the Arecibo Observatory in Puerto Rico (see Figure 23.6). This telescope is located in a natural sinkhole. The sinkhole formed when water flowing underground dissolved the limestone. This telescope would collapse under its own weight if it were not supported by the ground. There is a big disadvantage to this design. The telescope can only observe the part of the sky that happens to be overhead at a given time. A group of radio telescopes can be linked together with a computer. The telescopes observe the same object. The computer then combines the data from each telescope. This makes the group function like one single telescope. An example is shown in Figure 23.7. To learn more about radio telescopes and radio astronomy in general, go to | text | null |
L_0050 | telescopes | T_0492 | Radio telescopes collect radio waves. These telescopes are even larger telescopes than reflectors. Radio telescopes look a lot like satellite dishes. In fact, both are designed to collect and focus radio waves or microwaves from space. The largest single radio telescope in the world is at the Arecibo Observatory in Puerto Rico (see Figure 23.6). This telescope is located in a natural sinkhole. The sinkhole formed when water flowing underground dissolved the limestone. This telescope would collapse under its own weight if it were not supported by the ground. There is a big disadvantage to this design. The telescope can only observe the part of the sky that happens to be overhead at a given time. A group of radio telescopes can be linked together with a computer. The telescopes observe the same object. The computer then combines the data from each telescope. This makes the group function like one single telescope. An example is shown in Figure 23.7. To learn more about radio telescopes and radio astronomy in general, go to | text | null |
L_0050 | telescopes | T_0492 | Radio telescopes collect radio waves. These telescopes are even larger telescopes than reflectors. Radio telescopes look a lot like satellite dishes. In fact, both are designed to collect and focus radio waves or microwaves from space. The largest single radio telescope in the world is at the Arecibo Observatory in Puerto Rico (see Figure 23.6). This telescope is located in a natural sinkhole. The sinkhole formed when water flowing underground dissolved the limestone. This telescope would collapse under its own weight if it were not supported by the ground. There is a big disadvantage to this design. The telescope can only observe the part of the sky that happens to be overhead at a given time. A group of radio telescopes can be linked together with a computer. The telescopes observe the same object. The computer then combines the data from each telescope. This makes the group function like one single telescope. An example is shown in Figure 23.7. To learn more about radio telescopes and radio astronomy in general, go to | text | null |
L_0050 | telescopes | T_0492 | Radio telescopes collect radio waves. These telescopes are even larger telescopes than reflectors. Radio telescopes look a lot like satellite dishes. In fact, both are designed to collect and focus radio waves or microwaves from space. The largest single radio telescope in the world is at the Arecibo Observatory in Puerto Rico (see Figure 23.6). This telescope is located in a natural sinkhole. The sinkhole formed when water flowing underground dissolved the limestone. This telescope would collapse under its own weight if it were not supported by the ground. There is a big disadvantage to this design. The telescope can only observe the part of the sky that happens to be overhead at a given time. A group of radio telescopes can be linked together with a computer. The telescopes observe the same object. The computer then combines the data from each telescope. This makes the group function like one single telescope. An example is shown in Figure 23.7. To learn more about radio telescopes and radio astronomy in general, go to | text | null |
L_0050 | telescopes | T_0493 | Telescopes on Earth all have one big problem: Incoming light must pass through the atmosphere. This blocks some wavelengths of radiation. Also, motion in the atmosphere distorts light. You see this when you see stars twinkling in the night sky. Many observatories are built on high mountains. There is less air above the telescope, so there is less interference from the atmosphere. Space telescopes avoid such problems completely since they orbit outside the atmosphere. The Hubble Space Telescope is the best known space telescope. Hubble is shown in Figure 23.8. Hubble began operations in 1994. Since then it has provided huge amounts of data. The telescope has helped astronomers answer many of the biggest questions in astronomy. The National Aeronautics and Space Administration (NASA) has placed three other major space telescopes in orbit. Each uses a different part of the electromagnetic spectrum. The James Webb Space Telescope will launch in 2014. The telescope will replace the aging Hubble. To learn more about NASAs great observatories, check out | text | null |
L_0050 | telescopes | T_0493 | Telescopes on Earth all have one big problem: Incoming light must pass through the atmosphere. This blocks some wavelengths of radiation. Also, motion in the atmosphere distorts light. You see this when you see stars twinkling in the night sky. Many observatories are built on high mountains. There is less air above the telescope, so there is less interference from the atmosphere. Space telescopes avoid such problems completely since they orbit outside the atmosphere. The Hubble Space Telescope is the best known space telescope. Hubble is shown in Figure 23.8. Hubble began operations in 1994. Since then it has provided huge amounts of data. The telescope has helped astronomers answer many of the biggest questions in astronomy. The National Aeronautics and Space Administration (NASA) has placed three other major space telescopes in orbit. Each uses a different part of the electromagnetic spectrum. The James Webb Space Telescope will launch in 2014. The telescope will replace the aging Hubble. To learn more about NASAs great observatories, check out | text | null |
L_0050 | telescopes | T_0494 | null | text | null |