Space

Planet - Any of the nine large heavenly bodies revolving around the sun and shining by reflected light in the order of proximity to the sun.

Star -  Any of the planets, except the moon, appearing as fixed points in the night sky.

Gravity - The force of attraction between masses.

Galaxy - Large system of stars held together by gravitation and isolated from similar systems by vast regions at space.

Milky Way Galaxy - Galaxy that contains the solar system.

Universe - The whole world.

Mass - A body of coherent matter.

Weight - The amount of quanitity of heaviness or mass.

Natural satellite - is already made by nature e.g. moon.

Artificial satellite - is a man-made satellite.

Geostationary orbit - stays above same point on earth.

Polar orbit -  a orbit that passes over the poles of the earth.

Comet - Streams away from the sun leaving a trail of dust behind and gas.  It moves about the sun.

• Gravity is an attractive force that acts between all objects that has mass.  The size of the force depends on the mass of the object.

• The force of gravity between two objects depends on the mass of the objects and also the distance between them.

• The greater the distance between the masses, the weaker the pull would be.

• A satellite is any object that orbits another object.  There are 2 different types of satellites; natural and artificial.
• Natural satellite would be a moon or a comet.  Artificial satellite would be a communication satellite of weathering satellite.
• The moon is kept in orbit by the attraction of the Earth's gravity.  An artificial satellite is made by and put into orbit by humans.
• There aer two different types of satellite orbit.  They are; geostationary orbit and polar orbit.
• A geostationary orbit stays above the same point on the Earth.  Speed of orbit matches the Earth's rotation, so orbit time is 24hrs.
• Used for communication, satelite TV, weather forecasting, intelligence and global positioning (GPS)
• Polar orbit satellites are used for large-scale mapping and global weather monitoring.  Earth rotates underneath them as they orbit.  Low orbit around the Earth passing over North and South poles.
• Astronomical satellites are large telescopes.e.g. HST

The time taken for a satellite to go once round the orbit is called the time period.

speed = distance/time

v = (2   r)/T

If the radius of the satellite's circular orbit is r then the distance the satellite gas in one period is = 2   r.

v = speed of the satellite    metres/seconds (m/s)

r = radius of the orbit metres (m)

T = time for 1 orbit   seconds (s)

Comets are balls of dust and frozen gas. They have elliptical orbit.  The orbit arounfd the sun.  Gravity (from the sun) keeps them in order.

As the comet approaches the sun gases evaporate from it, forming a 'tail'.  This tail always faces away from the sun.

When it is flying toward the sun it is faster because the sun's gravitational pull is pulling it forwards.  When it is flying away from the sun it is slower because the sun's gravitational pull is trying to pull it back.