Celestial pole

“ Owing to the special form of the earth the north celestial pole is visible to us in the northern hemisphere, and marked very nearly by the pole-star, its height above the horizon being equal to the latitude of the place where the observer stands. Owing to the daily rotation of the earth the whole celestial sphere seems to revolve daily on the axis of the north and south celestial poles, carrying the sun, moon and stars with it. ”

“ For, the reeling motion of our earth has changed the place of the celestial pole in such a way as only to depress these constellations southwards without much changing their position; they are nearly upright when due south now as they were 4000 years ago, only lower down. ”

“ Afterward, wait twelve hours until that star returns to a position along the celestial meridian, this time north of the celestial pole [as all stars in the sky rotate around the celestial pole once in twenty four hours] . Then measure its height over the celestial horizon. When the second height measurement is subtracted from the first, and the remainder is divided in half and either added to the second measurement or subtracted from the first, and the result is the height of the celestial pole over the celestial horizon. ”

“ In the measurement of equatorial co-ordinates, the polar distance is determined in an analogous way. We determine the apparent position of an object near the pole on the celestial sphere at any moment, and again at another moment, twelve hours later, when, by the diurnal motion, it has made half a revolution. The angle through the celestial pole, between these two positions, is double the polar distance. ”

“ The adoption of the shaft or pole, as a symbol of the Celestial Centre, may easily be explained by the fact that, stuck into the ground and watched from a certain position, its upper end would seem to touch Polaris and it thus supplied wandering star-observers with a point of fixity in space which, being transportable, facilitated the registration of circumpolar rotation. ”

“ The gores of each are twelve in number, those of the terrestrial globe having an equatorial mounting while those of the celestial globe have an ecliptic mounting, that is, the meridian lines pass from pole to pole of the ecliptic instead of from pole to pole of the equator. In each, the gores have been truncated twenty degrees from the poles, the polar space being covered by circular discs. The engraving of both the terrestrial and the celestial map is exquisitely done, and much of the color originally applied by hand yet remains. ”

“ The twelve gores of the map have been mounted so as to join at the north and south poles of the ecliptic, there however being a small covering disc at each pole, so frequently employed since Mercator’s day, the globe itself being made to revolve on its equatorial axes. ”

“ Thus, after long intervals of time we find the pole of the earth no longer pointing towards the same spot in the apparent sphere of the heavens, or in other words, our pole-star is not, as at present, α Ursæ Minoris, but some other celestial body ”

“ The pole-star describes so small a circle that its motion can only with difficulty be detected with the naked eye, stars a little farther off the pole describe larger circles, and so on, until we come to stars half-way between the two poles, which describe the largest circle which can be drawn on the celestial sphere. The circle on which these stars lie and which is described by any one of them daily is called the equator. ”

“ Hence the celestial poles seem to continue in the same points of the Heavens throughout the year; which by no means disproves the Earth’s annual motion, but plainly proves the distance of the Stars to be exceeding great. ”

“ At the Poles, one half of the Ecliptic never sets, and the other half never rises: and therefore, as the Sun is always half a year in describing one half of the Ecliptic, and as long in going through the other half, ’tis natural to imagine that the Sun continues half a year together above the Horizon of each Pole in it’s turn, and as long below it; rising to one Pole when he sets to the other. ”

“ For a short time it remains stationary, then suddenly springs to life. The waves of light drive violently from east to west; the edges assume a deep red and green colour and dance up and down. The rays shoot up more rapidly; they become shorter; all rise together and approach nearer and nearer to the magnetic Pole. It looks as if there were a race among the rays, and that each aspired to reach the Pole first. And now the point is reached, and they shoot out on every side, to the north and the south, to the east and the west. ”