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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. Celestial 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 ...
Sextant. A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation . The estimation of this angle, the altitude, is known as sighting or ...
Meridian altitude is the simplest calculation of celestial navigation, in which an observer determines his latitude by measuring the altitude of an astronomical object at the time of its meridian contact. A meridian contact is the moment when the object contacts the observer's meridian, i.e. the imaginary line running north–south and through ...
Sextant (astronomy) In astronomy, sextants are devices depicting a sixth of a circle, used primarily for measuring the position of stars. There are two types of astronomical sextants, mural instruments and frame-based instruments. They are of significant historical importance, but have been replaced over time by transit telescopes, other ...
Being B the latitude (+N/-S), L the longitude (+E/-W). LHA = GHA + L is the local hour angle (+W/-E), Dec and GHA are the declination and Greenwich hour angle of the star observed. And Ho is the true or observed altitude, that is, the altitude measured with a sextant corrected for dip, refraction and parallax.
A modern astrolabe made in Tabriz, Iran in 2013. An astrolabe ( Greek: ἀστρολάβος astrolábos, 'star-taker'; Arabic: ٱلأَسْطُرلاب al-Asṭurlāb; Persian: ستارهیاب Setāreyāb) is an astronomical instrument dating to ancient times. It serves as a star chart and physical model of visible heavenly bodies.
The history of longitude describes the centuries-long effort by astronomers, cartographers and navigators to discover a means of determining the longitude of any given place on Earth. The measurement of longitude is important to both cartography and navigation. In particular, for safe ocean navigation, knowledge of both latitude and longitude ...
Sight reduction. In astronavigation, sight reduction is the process of deriving from a sight (in celestial navigation usually obtained using a sextant) the information needed for establishing a line of position, generally by intercept method . Sight is defined as the observation of the altitude, and sometimes also the azimuth, of a celestial ...