The Celestial Sphere

Most modern mariners are unfamiliar with the night sky. The stars are strangers and we become lost amongst the spinning celestial maze.

Think of the earth at the centre of a great sphere, with the stars and planets stuck on the inside (see Figure 8.1). We can only see half of this sphere so imagine a flat world with the sky as a great dome above our heads. Where the dome meets the earth is our horizon and our zenith is directly above our heads, shown in Figure 8.2.

The earth's rotation makes it look like the stars, planets, sun, and moon rise in the east, move across the sky and set in the west.

The only exceptions are stars near the north and south poles. These remain above the horizon and circle the pole. Their number varies with latitude: the higher your latitude, the more circumpolar the stars.

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