Saturday, February 12, 2011

The Story of the Australian Sun Part 1

The Story of Australia is also a story about our sunshine... especially in summer when we can suffer under days of scorching hot glare from our nearest star. Yet, without the sun, life on Earth (at least as we know it) would not be possible. However, the story of sunshine is almost told with the fear of one who names the demons in our dreams. Sunshine is the killer within... or at least that's how we see it through the lens of our society.

And even now that there's a cold change sweeping through South Australia (as in much of Australia in this very strange summer season this year), it's perhaps a good time to revisit the story of the Australian Sun.

The Sun
The Sun is a star...a pretty ordinary star as far as they go... it's name comes from Old English - but has connections to the Goddess Sunna (Germanic) and Sól (Norse)... and more distantly to the Sanskrit Surya. The light from the Sun is generated via a process of nuclear fusion where hydrogen atoms are fused to form Helium, which also releases a huge amount of energy as electromagnetic radiation (i.e. sunlight). This sunlight takes only about 8 minutes and 19 seconds to reach Earth. Once it gets here, it has the equivalent energy of about 1,368 Watts per square metre... although by the time it gets through the atmosphere it's closer to 1,000 Watts. Still, that's a good reason to get solar panels, even if they have at best only a 20% energy conversion efficiency.

Ultraviolet Light
Ultraviolet Light is just normal light that has a very low wavelength (which means it's beyond the violet end of the rainbow, in the part you cannot see with your eyes). This light has more energy than normal light, but less than X-rays. It is the UV rays (especially the UVB part) that are responsible for sunburns - not the visible part of the spectrum. It causes skin damage by breaking down collagen (which gives skin elasticity) and Vitamin A. It also generates nasty chemicals known "free radicals" which cause damage to your skin cells DNA.
Care of Wikipedia.

Most UV light from the sun never reaches the Earth's surface, as it gets adsorbed in the Ozone Layer...

The Ozone Layer
In fact, ever since the discovery of the Ozone Hole above the Antarctica in 1985, there has been a growing concern about the impact of ultraviolet (UV) radiation on Australia... and we often cited the ozone hole has being the cause of apparent increases in skin cancer and the almost universal opinion that the sun is hotter now than it used to be.

Now ozone is a form of oxygen (normally oxygen forms as O2, i.e. two oxygen atoms combined, whereas ozone is a form that combines three oxygen atoms, i.e. O3). Ozone is actually poisonous to people at ground level, but in the stratosphere around 15-40 km above us, it forms an important component in a chemical cycle that results in the absorption of harmful UV rays. This cycle sees normal O2 oxygen adsorbing light and splitting then recombining to form O3, which then adsorbs more UV light to break back into single Oxygen atoms before reforming with O2 to more O3. That seems pretty complicated... but what does all this mean?Well it means that the presence of ozone is important in the adsorption of UV light... and if that O3 is broken before it adsorbs UV then less UV is adsorbed... and the more that hits the Earth (that's you and me).

The global push to ban CFC (chlorofluorocarbons, a particular type of chemical structure that was often used in propellants and refrigerants, and which is one of those chemical types that breaks the ozone up) seems to have lead to a recovery in the ozone layer. However, the reality is that your latitude is the most important aspect of your UV exposure. The closer to the equator, the more you'll generally get, as shown below.
Care of The UN Environemtal Program and GRID-Arendal

UV Index
The current picture over Australia looks like the map where the numbers represent the UV index (Extreme  >11+ and you should avoid going out in the midday sun, Very High = 8 -10, High and you should wear protection and avoid any extended period in the sun, High = 6 -7 you should still wear protection and reduce time in the midday sun, Moderate 3-5 means you have a low risk but should still wear sunscreen if out in the sun for any length of time, whilst <3 represents no real danger to most people). Despite what a commonly held belief here in South Australia, it's generally much worse in the north for UV than down here in Adelaide. Yet, even here we'll start to develop a sun-tan after even 15mins in the sun during summer. Note - last year I spent a long time walking around in the sun in Japan, and hardly got tanned at all... and I have to admit that I loved it.... but the reality was that I was most probably still getting reasonable doses of UV.

The latest UV rating across Australia (care of BOM).

UV - The Untold Health Story
Something that is often overlooked with UV however is that it is critical in the production of Vitamin D (or D3 to be more precise) in people which is important in a range of biological factors. Vitamin D is important in the prevention of rickets which leads to the deformities of bones in young bodies. The related Vitamin D2 can however be obtained through food, although there is still no definitive determination whether these have the same physiological effects. In recent years there has been a push to increase people's awareness of the positive aspects of UV radiation, and it's recommended that people get at least 5-8 minutes (in Australia at least) exposure to the sun every day in summer, and up to 40 minutes per day in winter (obtained from a helpful articles here and here). The bottom line is that some sunlight is actually healthy - and therefore you shouldn't avoid it completely.

Care of the SunSmart organisation

Still - the message about UV has not been a happy one over recent times... and in today's world it begins and ends with skin cancer.... and that's a different story that's coming up next.

No comments:

Post a Comment