An orbiting satellite is any object encircling a planetary body in an orbit based on the gravitational force on that object. When hearing the word satellite, the TV signal relay equipment flying around Earth are what come to mind, but natural examples include moons around a planet, rings of cosmic debris around the large gas planets, and even the planets around the sun. In contrast, the manmade satellites orbiting Earth consist of items put into orbit on purpose and debris put there unintentionally, or at least without much thought.
Debris and Space Junk
The U.S. Air Force plans on spending more than $850 million to track nearly half a million pieces of orbiting space junk in a project called Space-based Space Surveillance (SBSS). All but approximately 21,000 pieces of debris from previous space missions are smaller than 4 inches in diameter (Space.com). The larger pieces are of concern because they could stop being satellites and become meteors if the orbit is pulled close enough to Earth.
Types of Satellite Orbits
There are generally three types of described orbit patterns for satellites circling Earth: geostationary, polar, and inclined.
Geostationary orbit means geosynchronous. These satellites are in sync with the Earth’s rotation in a way that leaves the satellite in the same position relative to the planet. The satellites provide poor views of the polar regions because they are in the equatorial plane (i.e. equatorial orbit). These types of satellites can monitor weather and are found at 35,790 km above Earth.
Polar orbits are at 700-800 km above Earth’s surface and inclined 90 degrees. These satellites are in sync with the sun, passing each latitude at the same time each day. Long-term comparisons are possible with images taken by satellites in this orbit. To keep pace with Earth’s rotation, the satellites rotate about one degree per day.
Inclined orbits range between 0 and 90 degrees. They are usually a few hundred kilometers above Earth and have an orbital time of a few hours. The exact specifications depend on their use and the area of interest on Earth. More information on types of orbits is available from NASA. NASA also offers a 3D method of tracking roughly 900 satellites currently in orbit around Earth at J-Track.
Satellites in the Night Sky
Some satellites can be seen from Earth with the naked eye because they reflect the sun (Space.com). NASA recommends this site to track when a satellite might pass overhead. The International Space Station may also be seen among the satellites in the sky, which can outshine stars as they move across the field of view. Approximately 10,000 satellites orbit Earth – put there to provide GPS (global positioning system) coordinates, television programs, radio broadcasts, communication, atmospheric monitoring, scientific measurements, and to take images, of both Earth and Space – and even to spy on others. For a list of examples see iO9.