sight reduction tables for air navigation pdf

An observer located anywhere on the circumference of this circle on Earth, measuring the angle of the same celestial body above the horizon at that instant of time, would observe that body to be at the same angle above the horizon.) Sights on two celestial bodies give two such lines on the chart, intersecting at the observer's position (actually, the two circles would result in two points of intersection arising from sights on two stars described above, but one can be discarded since it will be far from the estimated position-see the figure at example below). (The LOP is actually a short segment of a very large circle on Earth that surrounds the GP of the observed celestial body. After some computations, referred to as sight reduction, this measurement is used to plot a line of position (LOP) on a navigational chart or plotting worksheet, the observer's position being somewhere on that line. The measured angle between the celestial body and the visible horizon is directly related to the distance between the celestial body's GP and the observer's position. The latitude and longitude of that point is known as the celestial body's geographic position (GP), the location of which can be determined from tables in the nautical or air almanac for that year. Equally celestial navigation may be used whilst on other planetary bodies to determine position on their surface, using their local horizon and suitable celestial bodies with matching reduction tables and knowledge of local time.įor navigation by celestial means when on the surface of the earth for any given instant in time a celestial body is located directly over a single point on the Earth's surface. In addition, observations between stars and other celestial bodies accomplished the same results whilst in space - and was use extensively in the Apollo space program as well as currently on many contemporary satellites. The Moon, a planet, Polaris, or one of the 57 other navigational stars whose coordinates are tabulated in any of the published nautical almanac or air almanacs can also accomplish this same goal.Ĭelestial navigation accomplishes its purpose by use of angular measurements (sights) between celestial bodies and the visible horizon to locate one's position on the world, whether on land, in the air or at sea.

This angular observation combined with knowing its simultaneous precise time referred to the time at the prime meridian directly renders a latitude and longitude fix at the time and place of the observation by simple mathematical reduction. Celestial navigation can also take advantage of measurements between celestial bodies without reference to the earth horizon, such as when the moon and other selected bodies are utilized in the practice called 'Lunars' or lunar distance method, used for determining precise time when time is unknown.Ĭelestial navigation by taking sights of the Sun and the horizon whilst on the surface of the earth is commonly used, providing various methods of determining position, one of which is the popular and simple method called 'noon sight navigation'-being a single observation of the exact altitude of the sun and the exact time of that altitude (known as 'local noon')-the highest point of the sun above the horizon from the position of the observer in any single day. the Sun, the Moon, a planet, or a star) and the visible horizon. A diagram of a typical nautical sextant, a tool used in celestial navigation to measure the angle between two objects viewed by means of its optical sight.Ĭelestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space (or on the surface of the earth) without having to rely solely on estimated positional calculations, commonly known as ' dead reckoning', made in the absence of satellite navigation or other similar modern electronic or digital positioning means.Ĭelestial navigation uses 'sights', or timed angular measurements, taken typically between a celestial body (e.g.

Sight reduction tables for air navigation pdf