Astronomical Navigation - Tesina

English:

Astronomical navigation

Fire systems

Istituto Tecnico Nautico Luigi Rizzo – Materia: Inglese

Sergio Calabrò – Classe: V ATM – a.s. 2012/2013

Astronomical navigation

Until the compilation of new astronomical tables to assist the air navigator in obtaining a quick position by celestial observations, the solution of a Sun, Moon, or star sight, by which a position line on a chart could be obtained, required a knowledge of spherical trigonometry and the solving of what is known as the PZX triangle, where P is the position of the celestial pole, Z is the observer’s zenith (i.e., the point in the sky directly overhead), and X is the celestial body. The triangle is solved by calculations on the lines of the Cosine Theory and involves extensive use of mathematical tables.

But the new air navigation tables, now in wide use by many navigators at sea, have made the solutions very much simpler, and with these and Nautical Almanac, a navigator can obtain his true position without the long calculations previously necessary. From his observed altitude of the celestial body, a navigator obtains from the tables the true zenith distance of the body and from the Nautical Almanac the zenith distance from his dead reckoning or assumed position. The difference between these two distances is known as the intercept, and shows the navigator how far his real position is from his assumed position in one direction. He finds this direction from the exact time at which he took his sight which, from the tables, gives him the Greenwich Hour Angle.

His assumed longitude then gives him the Local Hour Angle and, using the body’s declination from the Nautical Almanac, the azimuth, or bearing, is obtained. By drawing this bearing on the chart from his assumed (DR) position and measuring off the intercept, a line drawn through that point at right angles to the azimuth provides a position line. A similar sight taken at the same time of a second celestial body on a different bearing will provide a second position line and the observer’s true position is at the point of intersection of these two position lines. An alternative method for use during daylight hours when the Sun is normally the only celestial body in sight is to take a second observation of the Sun some 3 or 4 hours later when its azimuth has altered sufficiently to provide a satisfactory angle of cut, which should never be less than 30 degrees.

Fire systems

Fire protection

The basic fire-fighting medium is seawater, supported by steam smothering CO₂, foam, and portable extinguisher systems in particular areas.