Compass has a half-life of only about 12 years, so a compass that contains 120 mCi of tritium when new will contain only 60 when it is 12 years old, 30 when it is 24 years old, and so on. Consequently, the illumination of the display will fade. Mariners' compasses can have two or more magnets permanently attached to a compass card, which moves freely on a pivot. A "lubber line", which can be a marking on the compass bowl or a small fixed needle, indicates the ship's heading on the compass card. Traditionally the card is divided into thirty-two points
Sun compass in animals Sun compass in animals Many animals are able to navigate using the Sun as a compass. Orientation cues from the position of the Sun in the sky are combined with an indication of time from the animal's internal clock. There is evidence that some animals can navigate using celestial cues, such as the position of the Sun. Since the Sun apparently moves in the sky, navigation by this means also requires an internal clock. Many animals depend on such a clock to maintain their circadian rhythm. Animals that use sun compass orientation are fish, birds, sea turtles, butterflies, bees, sandhoppers,