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bit about hydrogen and helium but my excuse is that they make up the bulk of the visible matter in the Universe. Similarly wavelengths, which, like frequency, can be used to describe the behaviour of different kinds of solar energy from X-rays to radio waves. You do not have to be a geek to appreciate such matters, witness a useful mnemonic for the relationship between wavelength and frequency to be found in one of the tales of diplomatic life by Lawrence Durrell: " If there is anything worse than a soprano, " said Antrobus judicially, as we walked down the Mall towards his club, " it is a mezzo-soprano. One shriek lower in the scale, perhaps, b ut with higher candle-po wer . " Just bear in mind that he got it the wrong way round. There are many paradoxes in my account. The Sun drives the weather and keeps the Earth's temperature at tolerable levels, it is the basis of photosynthesis and thus the life of plants and the creatures they sustain, and its magnetic field shelters us from dangerous cosmic rays; yet at the same time the ultraviolet (UV) part of the solar spectrum may damage DNA and human tissue, solar flares can destroy spacecraft, power systems and computers, and there is every indication that the Sun precipitated a mini Ice Age less than two centuries ago. Sunshine allows us to generate vitamin D but too much of it can lead to skin cancer and cataracts. Etcetera etcetera.
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