To understand what satellites can do, lets look at an example. One of the deadliest hurricanes in United States history hit Galveston, Texas in 1900. The storm was first spotted at sea on Monday, August 27th , 1900. It was a tropical storm when it hit Cuba on September 3rd . By September 8th , it had intensified to a hurricane over the Gulf of Mexico. It came ashore at Galveston (Figure 2.34). Because there was not advanced warning, more than 8000 people lost their lives. Today, we have satellites with many different types of instruments that orbit the Earth. With these satellites, satellites can see hurricanes form at sea. They can follow hurricanes as they move from far out in the oceans to shore. Weather forecasters can warn people who live along the coasts. These advanced warning give people time to prepare for the storm. They can find a safe place or even evacuate the area, which helps save lives. Satellites orbit high above the Earth in several ways. Different orbits are important for viewing different things about the planet. A satellite in a geostationary orbit flies above the planet at a distance of 36,000 km. It takes 24 hours to complete one orbit. The satellite and the Earth both complete one rotation in 24 hours. This means that the satellite stays over the same spot. Weather satellites use this type of orbit to observe changing weather conditions over a region. Communications satellites, like satellite TV, use this type of orbit to keep communications going full time. Another useful orbit is the polar orbit (Figure 2.35). The satellite orbits at a distance of several hundred kilometers. It makes one complete orbit around the Earth from the North Pole to the South Pole about every 90 minutes. In this same amount of time, the Earth rotates only slightly underneath the satellite. So in less than a day, the satellite can see the entire surface of the Earth. Some weather satellites use a polar orbit to see how the weather is changing globally. Also, some satellites that observe the land and oceans use a polar orbit. The National Aeronautics and Space Administration (NASA) has launched a fleet of satellites to study the Earth (Figure 2.36). The satellites are operated by several government agencies, including NASA, the National Oceano- graphic and Atmospheric Administration (NOAA), and the United States Geological Survey (USGS). By using different types of scientific instruments, satellites make many kinds of measurements of the Earth. Some satellites measure the temperatures of the land and oceans. Some record amounts of gases in the atmosphere, such as water vapor and carbon dioxide. Some measure their height above the oceans very precisely. From this information, they can measure sea level. Some measure the ability of the surface to reflect various colors of light. This information tells us about plant life. Some examples of the images from these types of satellites are shown in Figure 2.37. In order to locate your position on a map, you must know your latitude and your longitude. But you need several instruments to measure latitude and longitude. What if you could do the same thing with only one instrument? Satellites can also help you locate your position on the Earths surface. By 1993, the United States military had launched 24 satellites to help soldiers locate their positions on battlefields. This system of satellites was called the Global Positioning System (GPS). Later, the United States government allowed the public to use this system. Heres how it works. You must have a GPS receiver to use the system (Figure 2.38). You can buy many types of these in stores. The Prior to the late 20th and early 21st centuries, mapmakers sent people out in the field to determine the boundaries and locations for various features for maps. State or county borders were used to mark geological features. Today, people in the field use GPS receivers to mark the locations of features. Map-makers also use various satellite images and computers to draw maps. Computers are able to break apart the fine details of a satellite image, store the pieces of information, and put them back together to make a map.
Output: type of orbit that allows a satellite to stay over the same location on Earths surface