On Sunday evening I would not have known that the summer solstice was upon us – thick wavy clouds created a ceiling over the day and midges marred the evening.
Darkness was nearly upon us before 10.30pm. Despite the usual disappointment of the purportedly longest day of the year it did turn my thoughts to the sun, radiating silently above the waves of clouds.
The sun's radiation is what creates the right
conditions for life on Earth, without it life could not be sustained here. Infra-red light reaches the Earth in significant amounts and is chiefly responsible for the warming effect of solar radiation. The warmth is created by the relative short waves of this abundant light vibrating the molecules of living and inanimate objects.
Cold-blooded creatures like lizards and butterflies require a few seconds of this boost to revive them for the start of the day.
Whether the reception of radiation is good or bad for a thing depends on three factors. The first is the amount of energy that the radiation carries. Short-wave radiation has more energy than long-wave and therefore is more likely to be more dangerous. X-rays and gamma rays are the shortest electromagnetic waves, with wavelengths less than 1,000 millionths of a centimetre, these can be very dangerous to living cells.
The second is the dose that is received. This depends on the amount that reaches the Earth's surface. The atmosphere filters out most of the gamma and x-radiation so that the amount reaching our surface from space is virtually zero.
The third consideration is whether the living material absorbs the particular radiation; its energy may be transferred to it; or it may be reflected by its surface there by absorbing only a small amount of energy, or it may simply pass through it with no interaction with the atoms of that living thing.
While the sun radiates over the white electromagnetic spectrum the Earth's atmosphere is only transparent to infra-red, visible, and some ultraviolet light. These three have by far the greatest effect on living things.
Ultraviolet light has both negative and positive aspects. Generally, its effect is bad because it not only vibrates the molecules of living tissues, but it interferes with the chemistry of organic molecules when it infiltrates them. One of its repercussions is to cause genetic mutations, while UV may have assisted in the process of evolution, in the short term these light-sourced mutations become cancerous. Some animals, like bees, can see the longer waves of UV light. Fungi and coral contain specific pigments to protect them from this potentially harmful light.
The visible light from the sun is used by creatures as a guide of when to breed, when to sleep, germinate, flower, fruit or drop leaves. In fact, the length of day is more likely than temperature to be used as a sign of which season it is.
Even earthworms have light-sensitive cells in their skin allowing them to mark the difference between day and night. When these cells are overlaid with lenses they focus the visible light, creating the beginnings of true vision.
I react to the sunlight in different ways depending on what mood I am in or what I have to do on a particular day. I hate when the sun shines on the day of a funeral because she seems to infiltrate the emotions – interferes with them.
Maybe she reminds us that we are still alive in the continual cycle of life with her radiation at the helm.
