No measurable UVC from solar radiation reaches the Earth's surface, because ozone, molecular oxygen and water vapor in the upper atmosphere completely absorb the shortest UV wavelengths.
A suntan is a reaction to exposure to harmful UVB rays. Essentially, a suntan results from the body's natural defense mechanism kicking in. This consists of a pigment called melanin, which is produced by cells in the skin called melanocytes. Melanin absorbs UV light and dissipates it as heat. When the body senses sun damage, it sends melanin into surrounding cells and tries to protect them from sustaining more damage.
The pigment causes the skin to darken. However, continued exposure to UV radiation can overwhelm the body's defenses. When this happens, a toxic reaction occurs, resulting in sunburn. UV rays can damage the DNA in the body's cells. The body senses this destruction and floods the area with blood to help with the healing process. Painful inflammation occurs as well. Usually within half a day of overindulging in the sun, the characteristic red-lobster look of a sunburn begins to make itself known, and felt.
Sometimes the cells with DNA mutated by the sun's rays turn into problem cells that don't die but keep proliferating as cancers. The result is skin cancer, the most common form of cancer in the United States.
The UV Index and the sun protection times The sun protection times are issued when UV levels are forecast to be 3 or higher. You can find the sun protection times for your location: on our free SunSmart app on the SunSmart widget at the Bureau of Meteorology website.
Is temperature related to UV? The temperature can peak in the afternoon when UV levels are less intense. Why is the UV so high in Australia? Australia experiences some of the highest levels of UV in the world. Different factors affect our UV levels including: location: UV levels are highest along the equator. Australia is near the equator so we experience high UV levels time of year: our elliptical orbit around the sun and our axial tilt combine to ensure that we are closer to the sun in our summer than the northern hemisphere e.
How does UV add up? Health effects of too much UV radiation Too much UV radiation can cause skin and eye damage, sunburn, tanning and skin cancer. Sunburn Sunburn is a UV radiation burn to the skin.
Studies suggest that phototherapy can help treat unresponsive and severe cases of several diseases, including:. Phototherapy involves exposing a patient to a carefully monitored dose of UV radiation on a regular schedule. While this type of therapy does not eliminate the negative side-effects of UV exposure, treatment is carefully supervised by a doctor to ensure that the benefits outweigh the risks.
UV rays are strongest in areas close to the equator. Because the sun is directly over the equator, UV rays only travel a short distance through the atmosphere to reach these areas. UV radiation is also the strongest near the equator because ozone in these areas is naturally thinner, so there is less to absorb the UV radiation. UV exposure is lower in areas further from the equator because the sun is farther away. UV exposure is also greater in areas of snow, sand, pavement, and water due to the reflective properties of these surfaces.
Altitude is another contributing factor to the amount of UV. Higher altitudes have greater UV exposure because there is less atmosphere to absorb UV rays.
During the summer months the sun is in a more direct angle, resulting in a greater amount of UV radiation. UV is most intense at noon when the sun is at its highest point in the sky, and UV rays have the least distance to travel through the atmosphere. Especially in the hot summer months, it is a good idea to remain indoors during the peak sun hours of 10am and 4pm. Many people believe that you cannot get sunburned on a cloudy day; this is simply not the case.
Even under cloud cover it is possible to damage your skin and eyes, and cause long-term damage. It is important that you protect yourself with sunscreen, even in cloudy weather. Some surfaces, such as snow, sand, grass, or water can reflect much of the UV radiation that reaches them. The daily UVI forecasts the amount of UV reaching your area at noon when the sun typically reaches its highest point in the sky. Ultraviolet wavelengths of sunlight are made up of UVB, which has shorter wavelengths of to nanometres and higher energy, and UVA, which has longer wavelengths to nm and lower energy.
Both types of UV damage skin cells and both are thought to contribute to skin cancer. So the "alert" applies to the block of time the UVI is 3 or above though the course of any day. To some extent, the moderate to very high labels tell us little except that UV intensity is increasing.
The most simple advice is that when the index is at 3 or higher, protect your skin. Hence the "alert". To illustrate, today in Cairns the period when sun protection was needed was 8. In Hobart , the alert ran from 8. The Bureau of Meteorology has live UV meters for more accurate, on-the-spot local readings around the country.
There the UVI rarely gets into the extreme range. In Australia, we spend most of the summer with "extreme" UV conditions in the middle of the day.
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