One of the best ways to form an idea of the whole size of the sun is to imagine it to be hollow, like an air-ball, and then see how many earths it would take to fill it.  You would hardly believe that it would take one million, three hundred and thirty-one thousand globes the size of our world squeezed together.  Just think, if a huge giant could travel all over the universe and gather worlds, all as big as ours, and were to make first a heap of merely ten such worlds, how huge it would be!  Then he must have a hundred such heaps of ten to make a thousand world; and then he must collect again a thousand times that thousand to make a million, and when he had stuffed them all into the sun-ball he would still have only filled three-quarters of it!

After hearing this you will not be astonished that such a monster should give out an enormous quantity of light and heat; so enormous that it is almost impossible to form any idea of it.  Sir John Herschel has, indeed, tried to picture it for us.  He found that a ball of lime with a flame of oxygen and hydrogen playing round it (such as we use in magic lanterns and call oxy-hydrogen light) becomes so violently hot that it gives the most brilliant artificial light we can get — such that you cannot put your eye near it without injury.  Yet if you wanted to have a light as strong as that of our sun, it would not be enough to make such a lime-ball as big as the sun is.  No, you must make it as big as 146 suns, or more than 146,000,000 times as big as our earth, in order to get the right amount of light.  Then you would have a tolerably good artificial sun; for we know that the body of the sun gives out an intense white light, just as the lime-ball does, and that , like it, it has an atmosphere of glowing gases round it.

But perhaps we get the best idea of the mighty heat and light of the sun by remembering how few of the rays which dart out on all sides from this fiery ball can reach our tiny globe, and yet how powerful they are.  Look at the globe of a lamp in the middle of the room, and see how its light pours out on all sides and into every corner; then take a grain of mustard-seed, which will very well represent the comparative size of our earth, and hold it up at a distance from the lamp.  How very few of all those rays which are filling the room fall on the little mustard-seed, and just so few does our earth catch of the rays which dart out from the sun.  And yet this small quantity (1/2000-millionth part of the whole) does nearly all the work of our world. (These and the preceding numerical statements will be found worked out in Sir J. Herschel’s ‘Familiar Lectures on Scientific Subjects,’ 1868, from which many of the facts in the first part of the lecture are taken.)