But orbits can change over time, and with more satellites, the chance of a crash increases. In , an American satellite and a Russian satellite accidentally collided in space. Watch NASA scientists avert a close call between two satellites. When it comes to satellites, it's all about the orbit. Space scientists decide on the orbit for a satellite depending on its job. Some satellites orbit at a low altitude, just a few hundred miles above the Earth.
Others orbit the Earth thousands of miles out in space. Some orbit around the Earth's equator and others go over Earth's north and south poles. Low Earth orbit LEO satellites orbit in a region between miles to miles km above Earth. These satellites may orbit the earth many times a day and are often used for observing the earth. Many of these are polar-orbiting satellites that orbit Earth in a north-south direction from pole to pole.
As the earth spins below them, these satellites can scan the entire glove. Medium-Earth orbits MEO satellites orbit at an altitude between 1, miles and 22, miles 2,, km above the earth.
Navigation satellites work well at this altitude. Geostationary satellites, often used for communication, orbit Earth at an altitude greater than 22, miles 36, km. These satellites orbit Earth from west to east over the equator. Their orbital period is the same as Earth's rotation period : 24 hours.
Because they move in the same direction and speed as Earth is spinning, they are always above the same location, so from the ground they don't appear to be moving. In the picture below, the yellow areas show what part of Earth each kind of satellite sees during its orbit. Satellites are used for many purposes. Even though they are hundreds or thousands of miles out in space, satellites are part of our everyday life on Earth. They make us safer, broadcast entertainment, and make life more convenient.
Without satellites, some of us couldn't watch television, or figure out how to travel from one place to another. Some of us might be endangered by bad weather that we didn't know was coming, or we might be unable to make a long-distance phone call. Satellites often affect our lives without our even realizing it. Let's take a look at some of the jobs satellites do. Communication satellites allow television, radio, internet and telephone signals to be sent live anywhere in the world.
Before satellites, long-distance transmissions were difficult and had many barriers. But with satellites, signals can be beamed from one location upward to a satellite and almost instantly be redirected down to many locations anywhere on the earth. Today, much of what you see on TV is transmitted by satellite signal.
Communication satellites allow video conferencing for businesses and classrooms. Where people live far from cities, communication satellites provide access to education and medical help that would otherwise not reach them.
Satellites even allow your parents to use a bank card to make purchases at stores or gas stations. Learn more about communication satellites. In the past, people used the positions of the sun and the stars, maps, and compasses to find their way.
Today, satellite navigation systems such as GPS Global Positioning System allow people to figure out exactly where they are and how to get to where they want to go, making it almost impossible to get lost.
A system of 30 satellites circling the earth make up the Global Positioning System. The satellites constantly send out signals, your GPS receiver picks up those signals, and the distance from those satellites is calculated to determine your exact location. Often GPS receivers are built into cars and cell phones.
Other uses of GPS systems include use by military submarines for navigating under the sea, use of GPS for the treasure-hunt game of geocaching , and use of a handheld navigator that helps guide blind people to their destination. Learn more about GPS navigation satellites. First responders rely on satellites as they help people in trouble. The gravitational attraction between two objects decreases with distance. This means that the closer the two objects are to each other, the stronger the force of gravity between them.
If the force between them is greater, a greater acceleration will occur. The greater the acceleration, the greater the change in velocity - this causes the object to move faster. This means that objects in small orbits travel faster than objects in large orbits. Some passes are superior to others. If the ISS is not predicted to get much higher than degrees above your local horizon, odds are that it will not get much brighter than second or third magnitude degrees is roughly equal to the width of your fist held at arm's length.
In addition, with such low passes, the ISS will likely be visible for only a minute or two. Conversely, those passes that are higher in the sky — especially those above degrees — will last longer and will be noticeably brighter. The very best viewing circumstances are those that take the ISS on a high arc across the sky about 45 to 60 minutes after sunset, or 45 to 60 minutes before sunrise. In such cases, you'll have it in your sky upwards to four or five minutes; it will likely get very bright and there will be little or no chance of it encountering the Earth's shadow.
While the ISS looks like a moving star to the unaided eye, those who have been able to train a telescope on it have actually been able to detect its T-shape as it has whizzed across their field of view. Some have actually been able to track the ISS with their scope by moving it along the projected path.
Those who have gotten a good glimpse describe the body of the Space Station as a brilliant white, while the solar panels appear a coppery red. For evening passes , the ISS will usually start out rather dim and then tend to grow in brightness as it moves across the sky.
In contrast, for the morning passes, the ISS will already be quite bright when it first appears and will tend to fade somewhat toward the end of its predicted pass.
This is due to the change in the angle of sunlight hitting the vehicle. Lastly, remember that in certain cases, the ISS will either quickly disappear when it slips into the Earth's shadow during evening passes or quite suddenly appear when it slips out of the Earth's shadow during morning passes.
Conventional clock pendulums are constrained to one plane, pushed angularly by the Earth as it rotates. To keep a satellite's non-equatorial orbit rotating with the Earth instead of the stars would entail extra propulsion for a correspondence that can easily be accounted for mathematically.
Knowing that the period is 11 hours and 28 minutes, one can determine the distance a satellite must be from the Earth, and therefore its lateral speed.
Paul Dohrman's academic background is in physics and economics. He has professional experience as an educator, mortgage consultant, and casualty actuary. His interests include development economics, technology-based charities, and angel investing.
Definition of Elliptical Orbits. Have the Planets Changed Positions?
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