The guest speaker at the May meeting of Keighley astronomical society was Mr Rod Hine from our neighbours at Bradford Astronomical Society ‘Children of the Sun’, was the title of his presentation. Mr Hine explained that the energy provided by the Sun has to come in the right amount, shape and form to be useful to Life on Earth. Mr Hine had several table top experiments to prove his case.
Life cannot use X- rays or Radio waves as an energy source. Visible light from a G2 class star like our Sun is just right. The vegetation use it to make plant matter by photosynthesis, we and many other organisms use it to see by. Likewise, the amount of energy delivered by the Sun to our planet is just right for the hydrologic cycle to work, with water and water vapour changing back and forth, and some minor amount of ice (2 percent of the total water) collecting near the poles. Thus, the climate is between cold and warm, dry and wet, just about right.
The Sun sends light and heat rays (called infared, IR) and some ultraviolet light (UV). The UV is dangerous to living organisms; it damages eyes, human skin and tree leaves, among other things. Fortunately only a few percent of the energy arrives as UV, the rest is half visible light, half (invisible) IR. In addition, the atmosphere takes out most of the UV before it reaches the ground. The ozone layer in the lower stratosphere (just above the highest clouds) is especially important in protecting living things from UV exposure.
The amount and type of energy given off by the Sun corresponds closely to what is expected from its surface temperature (6000 degrees Kelvin). Stars hotter than the Sun are more bluish (and emit a relatively greater amount of UV radiation) and cooler stars are more reddish (with greater amounts of IR radiation). The visible light is made of many colours. We can see three of them (our brain constructs all sorts of colour hues from that information). Other organisms with eyes do not necessarily see the world the way we do; some cannot see colour, but some can see ultraviolet in addition to colour (many insects). Some have organs to sense infrared, for hunting warm prey (snakes).
The Sun is one of 100,000 million stars in the galaxy and about one quarter are much like it. Thus, there is no shortage of sun-like stars. We do not know, however, how many of these stars have a planetary system like ours. When taking questions from the audience, the type of exoplanets orbiting distant stars currently known was discussed. Mr Hine believes that there is little chance of life as we know it beyond our own small blue world.
Two thousand and five hundred years ago the Geek philosopher Anaxagoras claimed that the Sun is not a god (who adjusts energy output to human needs) but a huge ball of fire (which doesn’t particularly care about humans). This idea did not go over well, and resulted in exile for the philosopher, after a proper trial for impiety.