artificial light - frees people from the natural cycle of day and night created by the sun. Most artificial lights work by passing an electric current through a wire or a gas to make it glow.

electricity - is used to light and heat homes and to power motors in cars, trains and factories. It is a form of energy.

light - is a form of energy that travels freely in space. Most of the light we see comes originally from very hot objects (like the sun). Light has the highest speed of anything known - 300,00km per second through empty space.

shadows - Objects lit by a bright source of light cast shadows.

silhouette - is a dark shadow or outline seen against a light background or a profile portrait in solid black.

sun - is a globe of gas, mostly hydrogen, measuring 1392km across, over 100 times the diameter of the earth (compare a large pumpkin with a pea!). It is the centre of the solar system and gives the earth and other planets their light and heat. The temperature on the surface is about 6000 degrees Centigrade.