Celestial navigation Celestial navigation Celestial navigation, also known as astronavigation, is the ancient and modern practice of position fixing that enables a navigator to transition through a space without having to rely on estimated calculations, or dead reckoning, to know their position. Celestial navigation uses "sights", or angular measurements taken between a celestial body (e.g. the Sun, the Moon, a planet, or a star) and the visible horizon. The Sun is most commonly used, but navigators can also use the Moon, a planet, Polaris, or one of 57 other navigational stars whose coordinates are tabulated in the nautical almanac and air almanacs.
Abnormal profit Abnormal profit persists in the long run in imperfectly competitive markets where firms successfully block the entry of new firms. Abnormal profit is usually generated by an oligopoly or a monopoly; however, firms often try to hide this fact, both from the market and government, in order to reduce the chance of competition, or government intervention in the form of an antitrust investigation. In principle, there are three kinds of abnormal profit: Business writer Michael Porter and Anita M. McGahan undertook an empirical study of the "emergence and sustainability of abnormal profits" in 2003, in which they concluded that both