- Industry: Earth science
- Number of terms: 93452
- Number of blossaries: 0
- Company Profile:
Founded in 1941, the American Congress on Surveying and Mapping (ACSM) is an international association representing the interests of professionals in surveying, mapping and communicating spatial data relating to the Earth's surface. Today, ACSM's members include more than 7,000 surveyors, ...
A device consisting of a flat, reflecting surface adjustable to coincide with the plane of the horizon. The first practical form for use at sea was invented by A. Becher in 1838. It consisted of a small pendulum with its bob suspended in a cistern of oil. A form used on land consists of a dish or trough filled with mercury (or an amalgam of tin and mercury), the upper surface of which is free and horizontal. This form, modified by overlaying the mercury with a transparent, viscous fluid, has been used in making precise astronomical observations at sea and a similar form has been incorporated in some self leveling leveling instruments. Another form is a plane mirror of glass or other material fitted with spirit levels and leveling screws so that the mirror's surface can be adjusted into the plane of the horizon. The artificial horizon used for aerial navigation is usually kept parallel to the plane of the horizon by a gyroscopic pendulum. In observing a celestial object such as a star or the Sun, the angle is measured between the body as seen directly (with transit or theodolite) or by reflection (in the horizon glass of a sextant) and its image as seen reflected in the artificial horizon. This is a vertical angle and is double the angular elevation of the body.
Industry:Earth science
The arc of the celestial equator between the lower branch of the Greenwich celestial meridian and the hour circle of the Moon, measured westward from the lower branch of the Greenwich celestial meridian through 24 hours. Greenwich lunar time is equivalent to local lunar time at the Greenwich meridian and to the Greenwich hour angle of the Moon, expressed in units of time, plus 12 hours.
Industry:Earth science
The series of measurements, in a clockwise sequence from the farthest, known, visible object, of angles or directions to objects such as tanks, spires or signals, for identification of the objects and subsequent use of their angles or directions. Similar to a round of observations.
Industry:Earth science
A block of crust, formed by faulting and generally elongate, raised relative to the blocks on either side without much tilting or faulting.
Industry:Earth science
The science of measuring the humidity (relative water content) of air and other gases.
Industry:Earth science
An arbitrary, rectangular grid placed on an aerial photograph.
Industry:Earth science
A height (i.e., distance), as distinguished from quantities which are not distances but which are, by convention, called heights (e.g., dynamic height or thermal height)
Industry:Earth science
A grid system in a plane tangent to the ellipsoid and having its origin at the point of tangency. The origin is usually given the coordinates 10 000 E and 10 000 N, or some similar values, to keep all coordinates positive. This system never extends for any great distance.
Industry:Earth science
One of the six quantities r*, G, H, r, u, Ω used in the theory of orbits: r is length of the radius vector (the line from the origin to the satellite), u the angle from the equatorial plane to the radius vector and Ù the angle from a reference line in the equatorial plane to the projection of the radius vector onto that plane. R* is the rate of change of r, G is r²(du/dt) and H is G cos i, i being the inclination of the orbital plane to the equatorial plane.
Industry:Earth science
