27. SUN

Before leaving our solar system we should first start discussing the most nearest star in our galaxy: the SUN.
Nearest, but that is relatively: a sun with the size of 1 meter should show the earth as a marble at 100 meter distance! The sun is as star a quite common star, a dull mediocrity in all aspects, in size, in mass, in spectrum, in brightness, in temperature, etc.etc. Lucky for us, we would not be there, were all these aspects a little bit different.
Its energy is delivered by nuclear fusion processes in the core, where hydrogen is converted into helium under tremendous pressure and at very high temperatures. Its radiation stretches to outside the planetsystem, in particular the fatal very strong gammaradiation, X - ray radiation and ultraviolet radiation and, don't forget, the SOLAR WIND, consisting of particles of helium, hydrogen, protons, electrons, ions, etc. fired with very high speed (500 km/sec) and in large numbers into space. A non-protected man on the moon would disappear completely in a second! We, on earth, are protected by the VAN ALLEN BELTS, magnetic fields created by the core of the earth and bending the wind to the earthpoles ( Polarlight!).
The sun is still under investigation in particular by the SOHO-sonde, fixed at a location at ~1% (!) of the distance to the sun, the so-called "Lagrange point" where the gravitational attraction of earth and sun are equal. So we really don't need a solar-eclipse, no more endless waiting for such a show, we can do it now 24 hours per day!
What is the future of the sun? Well, say after a billion years the sun will become considerable brighter than today, he will become "a red giant", causing fast increasing temperatures, evaporating oceans on earth. It is for sure that then life on earth will become quickly impossible. Looking another 5-6 billion years further, the sunlight will be hundred times stronger than today and the sun start to shrink into a compact, white-hot core, a "white dwarf", the beginning of the end, dying, but that will take another trillion of years.