TLDR
The planets are all massive globes, more or less flattened at the Poles; but now we have to talk about a multitude of objects of the most irregular shapes, and of the most flimsy description. We call them comets, and they exist in such numbers that an old astronomer has said “there were more comets in the sky than fishes in the sea,” though I think we cannot quite believe him. There is also another wide difference between planets and comets: planets move round in nearly circular ellipses, and not only do we know where a planet is to-night, but we know where it was a month ago, or a hundred years ago, or where it will be in a hundred years or a thousand years to come. All such movements are conducted with conspicuous regularity and order; but now we are to speak of bodies which generally come in upon us in the most uncertain and irregular fashion. They visit us we hardly know whence, except that it is from outer space, and they are adorned in a glittering raiment, almost spiritual in its texture. They are always changing their appearance in a baffling, but still very fascinating manner. If an artist tries to draw a comet, he will have hardly finished his picture of it in one charming robe before he finds it arrayed in another. The astronomer has also his complaints to make against the comets. I have told you how thoroughly we can rely on the movements of the planets, but comets often play sad pranks with our calculations. They sometimes take the astronomers by surprise, and blaze out with their long tails just when we do not expect them. Then by way of compensation they frequently disappoint us by not appearing when they have been most anxiously looked for.via the TL;DR App
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Written by robertsball | I was an Irish astronomer who founded the screw theory.