Earth and Space

The Solar System consists of the Sun with planets in orbit around it. Most planets have at least one satellite in orbit around them.

 Gravity provides the centripetal force needed to keep objects in orbit.

We can explore space using manned or unmanned spacecraft.

The Solar System

Solar systems consist of:
    • a star (the Sun)
    • planets and dwarf planets in orbit around the Sun
    • satellites (moons) in orbit around most of the planets
    • comets and asteroids in orbit around the Sun.

There are eight planets in our solar system, including the Earth, and smaller dwarf planets such as Pluto.

A satellite:

is an object that orbits a larger object in space. 

The Moon is the Earth’s natural satellite. Other planets also have natural satellites. 

For example, Mars has two small natural satellites called Phobos and Deimos.

The Earth has many artificial satellites in orbit around it.

 These have been built by people and 

launched into orbit using rockets. Some very large artificial satellites were put into orbit by

 the American Space Shuttle.

„  Artificial satellites in orbit around the Earth have different orbits.

    Satellites in lower orbits travel faster than those in higher orbits. The higher the orbit of a satellite,
     the longer its
(time to make one orbit).

1- Satellite in a polar orbit:

Satellites in low orbit pass over the poles.
„They orbit between 100 km and 200 km above the Earth’s surface.
Taking around 90 minutes to make each orbit.
„The Earth spins beneath the satellite as it moves, so the satellite can scan the whole 
surface of the Earth.

Low orbit polar satellites have uses such as:
„monitoring the weather
„Observing the Earth’s surface
„military uses including spying.
 Google maps use a polar orbit satellite called ‘SPOT’

2- Satellite in a geostationary orbit:

„Geostationary satellites have a different trajectory to polar satellites they are in orbit above
 the equator (higher orbit).  
„ The height of their orbit - 36,000 km
„ It takes them one day (24 hours) to make each orbit.
„This means that they stay in a fixed position over the Earth’s surface.

Geostationary satellites have uses such as:

„Communications - including satellite TV
„Global positioning or GPS - which is used for sat navs (satellite navigation systems)
„Geostationary satellites always appear in the same position when seen from the ground. 
This is why satellite television dishes can be bolted into one position and do not need to move.