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THE CELESTIAL SPHERE VIEWED FROM A MIDDLE LATITUDE.

AN OBLIQUE SPHERE.

At O we imagine an observer to be in latitude 45° (that is, half-way between the equator in latitude 0°, and the North Pole in latitude 90°), hence the North Celestial Pole will be half-way between the zenith and the horizon; and close to the pole he will see the stars describing circles, inclined, however, and not retaining the same distance from the horizon. As the eye leaves the pole, the stars rise and set obliquely, describe larger circles, gradually dipping more and more under the horizon, until, when the celestial equator is reached, half their journey is performed below it. Still going south, we find the stars rising less and less above the horizon, until, as there were northern stars that never dip below the horizon, so there are southern stars which never appear above it. D D′ shows the apparent path of a circumpolar star; B B′ B″ the path and rising and setting points of an equatorial star; C C′ C″ and A A′ A″ those of stars of mid-declination, one north and the other south.