Is a star; is the centre of the solar system, as it is in consequence called, is a globe consisting of a mass of vapour at white heat, and of such enormous size that it is 500 times larger than all the planets of the system put together, or of a bulk one million and a half times greater than the earth, from which it is ninety-two and a half million miles distant; the bright surface of it is called the photosphere , and this brightness is diversified with brighter spots called faculæ , and dark ones called sun-spots , and by watching which latter as they move over the sun's disk we find it takes 25 days to revolve on its axis, and by means of spectrum analysis (q. v .) find it is composed of hydrogen and a number of vaporised metals.