The sun makes life on Earth possible. While the warmth and light provided are beneficial for many reasons, the dark side of the sun is the potential damage that can be caused by ultraviolet radiation. These facts about sunlight and UV rays, courtesy of the U.S. Environmental Protection Agency, the FactFile and NASA, can help people make more informed choices about spending time in the sun.

There are three types of UV rays. UVA reaches Earth’s surface because the atmosphere does little to shield these rays. UVA rays contribute to ailments like wrinkling and can penetrate through windows and clouds. UVB rays largely are thwarted by the atmosphere. However, latitude, altitude and time of year may increase the likelihood of UVB ray exposure, which is often the culprit behind skin cancer. UVC rays are completely absorbed by the Earth’s atmosphere and don’t pose a significant threat, even though they have the highest energy levels of all three types of UV rays.

The sun’s UV rays are strongest between 10 a.m. and 4 p.m., when the sun is at its highest in the sky. The ultraviolet radiation will be less severe early in the morning and later in the day.

Snow, water and sand reflect the damaging rays from the sun and can increase a person’s risk for sunburn.

The higher up in altitude a person goes, the stronger the sun’s rays become. Therefore, sun exposure in the mountains can be more dangerous than exposure at sea level.

Areas closest to the equator will get the longest hours of sunlight. The sun’s rays are much stronger near the equator.

Australia ranks near the top of the skin cancer risk list along with New Zealand. These countries are located close to the ozone layer hole over the Antarctic. In addition, during summer, the Earth’s orbit places Australia closer to the sun compared to other countries. That results in an additional solar UV intensity, according to Specialist Clinics of Australia.

UVA rays penetrate more deeply into the skin and can cause it to prematurely age.

UVB rays damage the outermost layers of the skin and contribute to the most skin cancers. Overexposure to UVB rays causes delayed sunburns.

While the sun is more intense during spring and summer, sun glare may be a bigger problem in the fall and winter. The sun during the colder months takes a lower angled route when rising, rather than seemingly going straight up, which it does in the summer. That keeps the sun in a blinding position for a longer period of time in the fall and winter.

The sun’s energy is produced by the fusion of hydrogen into helium. Nuclear reactions occur in the core of the sun due to temperature and pressure. The sun also emits infrared radiation, visible light and ultraviolet light.