Messages from Space

Messages from Space

Satellites circling the Earth send us pictures of the weather and relay telephone calls and television programs around the world. They also study vast areas of the Earth and its oceans, taking photographs and measurements with their cameras and instruments and beaming them down to Earth by radio. Some satellites circle the planet from pole to pole; others circle around the equator. Most satellites orbit the Earth at a height of between 124 miles and 496 miles and have to travel at a speed of 5 miles per second to stay in orbit.

Communications and weather satellites are boosted to a height of 22,320 miles (36,000 km) – much higher that other satellites. At this height above the equator, a satellite circles the Earth once every 24 hours, the same time the Earth takes the spin once on its axis. This kind of orbit is called  “geostationary” because the satellite seems to hover over the same spot on Earth. It takes three satellites in geostationary orbit to relay telephone calls between any two points on Earth.

Communications Satellites

A communications satellite or comsat, works a little like a mirror on the sky, it receives radio signals beamed up to it from Earth, amplifies them and sends them back to a different place on Earth.

A Live Broadcast

Satellites enable events such as the Olympic Games to be watched anywhere in the world seconds after the happen.

In the Sky

A low-flying satellite orbits at a height of about 155-186 miles just outside most of the Earth's atmosphere. It can dip down to as low as 74 miles to take close-up photographs of interesting places. Its advanced camera systems can see details as small as 2 inches across.

Messages from Space. Photograph by Elena.

Gas Tanks

The satellite uses jets of gas from its gas tanks to stop it from drifting out of position.

Communications Circuits

The satellite's communications circuits can relay tens of thousands of telephone calls at the same time.

Picturing the Weather

Satellite pictures can help a weather forecaster see how weather systems, such as cyclones, grow and move across the oceans. Views from the space would be impossible to obtain from the ground.

Weather Satellite's

The world's weather constantly changes, and the temperature of the sea, the land and the clouds vary all the time. A weather satellite carries heat-sensitive cameras that continually monitor the weather.

Staying on Orbit

If could throw a ball hard enough, it would fly all the way around the Earth, because the curve of its fall would exactly match the curve of the Earth's surface. To see this in action, make two plastic balls – one 2 in across to represent gravity, and one ¾ in across to to represent a satellite. Thread 20 in of string through a thread spool (Earth), and tie each end to a key. Push each key into one of the balls. Hold the thread spool and the large ball and start the small ball spinning. Let the large ball go. The satellite tries to fly away from Earth but gravity pulls it back. When the two forces are balanced, the satellite orbits Earth.

Messages from Space. Illustration by Elena.