The dying sun “Part 1” : https://steemit.com/article/@afzaalsabir/the-dying-sun-part-1
The dying sun “Part 2” : https://steemit.com/science/@afzaalsabir/the-dying-sun-part-2
The dying sun “Part 3” : https://steemit.com/science/@afzaalsabir/the-dying-sun-part-3
Is this important to remember the rarity of the event which produced our planetary system. Calculation shows that there can be only very few such systems in space. Yet, so far as we can see, life of the kind we know on earth can exist only on planets like the earth. It needs suitable physical conditions for its appearance, the most important of which is a temperature at which substances can exist in a liquid state
The stars themselves are far too hot for this. We may think of them as a collection of fires scattered through space, providing warmth in surrounding where the temperature is at most some four degrees above absolute zero, that is, about 484 degrees of frost on the Fahrenheit. In the immense stretches of space beyond the Milky Way, it is colder still. Away from the fires there is this un-imaginable cold of hundreds of degrees of frost; close up to them there is a temperature of thousands of degrees at which all solids melt, all liquids boil.
Life can exist only in a narrow belt surrounding each of these fires at a certain distance where the temperature is neither too hot nor too cold. Outstand these belts life would be frozen; inside it would be burnt up. A rough calculation shows that all such temperature belts, within which life is possible, all added together, make up less than a thousand million millionth part of the whole of space. And even inside. And even inside them, life must be very rare, for it is extremely unusual for suns to throw off plants as our sun has done. Probably only one star in 100,000 has planet going round it at the right distance for life to be possible on it.