Sun

Without the sun there would be no life on Earth.

The sun is an important source of vitamin D. Vitamin D helps the body metabolize calcium which is essential for the development and maintenance of healthy bones and therefore necessary for maintaining good physical health.

The sun is also a source of warmth and light and provides a general sense of well being.

Sunlight arrives on earth in many forms. Different types of light have different characteristics. Infrared light (heat), visible light and ultraviolet light. Ultraviolet light is classified into three categories.

UVA has a wavelength of 400-320 nm. It causes tanning but also speeds up the ageing of your skin. 99% of the sun's UV radiation at sea level is UVA.

UVB has a wavelength of 320-280 nm. It causes damage to the skin in the form of sunburn. Much of the UVB light is filtered out by the ozone layer, clouds and window glass but even small quantities can easily burn the skin if it is not protected.

UVC has a wavelength of 280-100 nm and is filtered out by the ozone layer in the atmosphere and never reaches us.