Orbit (original) (raw)

An is a regular, repeating path that one object takes around another object or center of . Orbiting objects, which are called , include , , , and artificial devices.

Objects orbit each other because of gravity. Gravity is the force that exists between any two objects with . Every object, from the smallest to the largest , has mass. The more massive the object, the larger its . Gravitational pull is the amount of force one object on another object.

The is the most massive object in our . All other objects in the solar system are subject to the gravitational pull of the sun.

Many satellites orbit on . An orbital plane is a flat, disk-shaped space that connects the center of the object being orbited with the center of orbiting objects. Because all planets in our solar system share a similar orbital plane, planets don't collide.

All the planets in our solar system line up with each other on the same general orbital plane. However, sometimes orbital paths of other objects in the solar system , and the objects can collide. , for instance, passes through orbit. The from the of this passes through Earth's as , or falling stars, at a specific time every year. The debris from the comet's orbit is called the .

The time it takes for an object to orbit around another object is called its . Earth's orbital period around the sun is complete in slighly over 365 days. The farther away a planet is from the sun, the longer its orbital period. The planet , for example, takes almost 165 years to orbit the sun.

Each orbit has its own . Eccentricity is the amount an orbit's path differs from a perfect circle. A perfect circle has an eccentricity of zero. Earth's eccentricity is 0.017. Mercury has the largest eccentricity of all the planets in the solar system, at 0.206.

Types of Orbits
orbit planets, while planets orbit the sun. Our entire solar system orbits the at the center of our , the . There are three major types of orbits: , , and geocentric orbits.

Galactocentric orbits circle the center of a galaxy. Our solar system orbits the Milky Way.

Heliocentric orbits go around stars. All the planets in our solar system, along with all the asteroids in the and all comets, follow this kind of orbit. Each planet's orbit is regular: They follow certain paths and take a certain amount of time to make one complete orbit. The planet Mercury completes its short heliocentric orbit every 88 days. may take 100,000 years to complete its heliocentric orbit.

A geocentric orbit is one that goes around Earth. Our moon follows a geocentric orbit, and so do most artificial satellites. The moon is Earth's only natural satellite. It takes about 27 days for the moon to complete its orbital period around Earth. There are three major types of geocentric orbits: (LEO), (MEO), and .

Low-Earth orbit exists between 160 kilometers (100 miles) and 2,000 kilometers (1,240 miles) above Earth's surface. Most artificial satellites with human crews are in low-Earth orbit. The orbital period for objects in LEO is about 90 minutes.

Medium-Earth orbit exists between 2,000 kilometers (1,243 miles) and 36,000 kilometers (23,000 miles) above the Earth's surface. Satellites in MEO are at greater risk for damage, because they are exposed to powerful from the sun. Satellites in MEO include and . MEO satellites can orbit Earth in about two hours.

Satellites in geostationary orbit circle Earth directly above the . These satellites have , or move at the same of Earth. Therefore, the orbital period of geosynchronous satellites is 24 hours.

Geostationary satellites are useful because they appear as a fixed point in the sky. pointed toward the geostationary satellite will have a clear signal unless objects in the atmosphere (such as storm clouds) between Earth and the satellite interfere. Most are geostationary and provide images of Earth's atmosphere.

Satellite Orbits
Artificial satellites are sent to orbit Earth to collect information we can only assemble from above the atmosphere. The first artificial satellite, , was launched by the in 1957. Today, thousands of satellites orbit Earth. Weather satellites provide images of weather patterns for to study. Communication satellites connect cellphone users and . track movement of weapons and from different countries.

Sometimes, artificial satellites have people on them. The most famous artificial satellite is the . from all over the world stay on the ISS for months at a time as it orbits Earth. and stargazers can see the ISS and other satellites as they orbit through and even powerful binoculars.

Not all artificial satellites orbit Earth. Some orbit other planets. The mission, for instance, is studying the planet . The project has a , Cassini, which orbited Saturn.

Putting satellites into orbit is and costly. Few can afford large space programs. Artificial satellites from the United States are sent into orbit by the National Aeronautics and Space Administration, or . The European Space Agency (ESA) launches satellites from countries in the . The Russian Federal Space Agency (Roscosmos), the Japanese Space Agency (JSA), and the Iranian Space Agency (ISA) are some of the governments that have successfully put satellites into orbit.

Satellites are put into orbit from , which are carefully for that purpose. The Baikonur Cosmodrome in Kazakhstan and the Kennedy Space Center in the U.S. state of Florida are both well-known spaceports.

Fast Fact

Clarke Orbit
The idea for geostationary orbit was outlined in a 1945 paper by the scientist and science-fiction author Arthur C. Clarke. For this reason, geostationary orbit is sometimes called "Clarke orbit."

Fast Fact

Edge of Orbit
Voyager II is a spacecraft launched by the United States in 1977. Voyager II passed through the heliosheath, the edge of the sun's gravitational pull, in 2007. Voyager II is outside the sun's orbit.

Fast Fact

Pluto
Pluto, a dwarf planet on the edge of our solar system, takes a strange orbit around the sun. Pluto's eccentricity is also much higher than any planet in the solar system, at 0.249. This is partly why Pluto, an official planet until 2006, was downgraded to a dwarf planet.

Fast Fact

Space Junk
There are more pieces of space junk orbiting Earth than useful satellites. Space junk is material from satellites, rockets, or other spacecraft that no longer works.