Geodesy is a science that uses mathematics, physics, astronomy, observation, and technology to measure the size and shape of the Earth, its gravitational field, and the movement of its crust. It provides accurate coordinates, distances, angles, and heights between points and helps in navigation, military operations, and scientific research. The study of geodesy dates back to ancient Greece, and it has evolved with technological advancements. Geodesists use a reference ellipsoid to measure the Earth efficiently.
Geodesy, sometimes called geodesics, is a science that applies mathematics to measure the size and shape of the Earth, the locations of points and regions on the Earth, and the differences in its gravitational field. This science uses principles of physics, mathematics and astronomy together with observation and modern technology to develop a spatial reference system. Geodesy also studies the movement of the earth’s crust, polar movement and tides. The work of geodesists includes giving points on Earth exact coordinates, accurately measuring distances, angles and heights between points, and observing how and why the Earth’s surface has changed over different periods of time.
Many major work camps depend on geodesy to function properly. Ships and planes use global positioning systems (GPS), maps and other navigation systems based on geodetic data to make sure they land in the correct place, avoid dangerous travel lanes and take the fastest and most fuel-efficient routes. Scientists in other fields, such as oceanographers or paleontologists, use geodetic data to examine the forces that cause changes in land surface features or topography. The military has long used geodesy to determine exact points to locate positions, control artillery, navigate and, later, track satellites and direct missiles.
Some historians argue that the study of geodesy began with the ancient Greeks’ first attempts to measure the size of the Earth. The first serious attempt to make accurate measurements, so far as we know, was pursued by the Greek scholar Eratosthenes in the 3rd century BC By measuring the angles of the shadows at two points on the Earth at a particular time of year, measuring the distance between the points and assuming that the two points lie in an exact north-south plane, Eratosthenes was able to make a surprisingly accurate approximation of the earth’s circumference. Despite some erroneous data, the scholar estimated the Earth to be 25,000 miles (40,233 km). Today, geodesists agree that Earth is approximately 24,901 miles (40,074 km) from the equator.
Several other ancient Greeks used similar methods, measuring the angles of stars with respect to two points on Earth, to make their own estimates and maps. The field of geodesy continued to evolve over the centuries, meeting rapid progress in the 17th century AD. During this period the telescope was developed, which allowed for greater precision in measuring the angles of objects in space; logarithms were invented, which allowed greater computational efficiency; and triangulation was discovered as a method of determining the position of a point. Using this new technology, French-Italian scholar Giovanni Domenico Cassini discovered that the Earth was not spherical, as previously thought, but elliptical, or egg-shaped.
Several techniques can be used to examine the three-dimensional shape and range of the Earth, as well as the positioning of the gravitational field. Most can be brought under the umbrella of land surveying, satellite imaging, and applied mathematics based on the data gleaned from the first two methods of observation. Because the Earth is highly irregular in shape, geodesists use a mathematical model of the Earth known as a reference ellipsoid to efficiently measure the Earth. The ellipsoid can be completely smooth, unlike the geoid, another model that represents the irregularity of the shape of the Earth and the variations in gravitational attraction. While the ellipsoid maintains the planet’s general shape, which is flatter at the poles and wider at the equator, the lack of topographical complexity makes calculations much simpler.
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