General facts about the Sun

The Sun is a star at the center of the Solar System around which orbits the Earth. It s composed of hydrogen (about 74% of its mass, or 92% of its volume), helium (about 25% of mass, 7% of volume), and trace quantities of other elements.

Ultraviolet Radiation (UVR)

The sun produces ultraviolet radiation (UVR) that gives us light to see, warmth, and fuel for the growth of plants.

• UVR has 3 different bands - UVA, UVB and UVC. Very little UVC reaches the earth's atmosphere. UVB is the strongest type and causes most sunburns. UVA is weaker than UVB, but about 100 times more UVA than UVB rays reach the earth's surface, meaning UVA protection is still important.
• Skin cancers, cataracts and 90% of visible aging (wrinkles) are caused primarily by UVB and UVA rays. Sunburn is caused primarily by UVB rays.
• The risk of skin cancer is believed to double for people who receive just one or two severe sunburns during childhood. In fact, researchers believe that 80-90% of the skin damage that causes wrinkles and skin cancer is received before the age of 18.
• Sunburn shows damage to the skin caused by UVB rays. However, just because the skins shows no visible signs of a burn does not mean it is not being damaged by the sun.

SPF Ratings

The sun protection factor (or SPF) measures the amount of sun protection provided against UVB rays ONLY. SPF does NOT measure the amount of protection provided against UVA rays. The SPF rating indicates how much longer it takes to get a sunburn using a sunscreen than it would without using it. For example, an SPF rating of "4" means it takes four times as long to get a sunburn, a rating of 20 means it takes 20 times as long.

• A tan only provides about the same amount of sun protection as a sunscreen of 3 SPF.
• For sun protection purposes skin is divided into 6 types. The Skin Types are:
• Type 1: Always burns, never tans (fair skin, light-eyes, freckles)
• Type 2: Usually burns, tans with difficulty
• Type 3: Sometimes burns, sometimes tans
• Type 4: Burns minimally, always tans
• Type 5: Rarely burns, tans profusely
• Type 6: Never burns, deeply tans (dark skin, dark eyes)

The Ozone Layer

Ozone is the gas that filters UVB rays from the atmosphere (ozone does not filter UVA rays). The size of the ozone layer (and the protection it provides from UVB varies based on the time of day, location, season and altitude).

• The ozone layer is at its thinnest in the tropics (UVR levels are 1,000 times higher at the equator than at the North or South Poles).
• The ozone layer is also thinner during the summer and fall, and from 10 a.m. to 2 p.m.
• Sand increases the intensity of UVRs by reflecting back most of the UVRs that reach the earth's surface - intensity can be increased by as much as 80%.
• Surprisingly, water reflects very little UVR and cloud cover reduces UVR that reaches the earth's surface - but the amount of protection is determined by the density of the cloud cover.
• The ozone layer provides much less protection from UVR at high altitudes