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The spherical shape of the Earth was known and measured by astronomers, mathematicians, and navigators from a variety of literate ancient cultures, including the Hellenic World, and Ancient India. Greek ethnographer Megasthenes , c. 300 BC , has been interpreted as stating that the contemporary Brahmans of India believed in a spherical Earth as ...
With a spherical Earth, half the planet is in daylight at any given time and the other half experiences nighttime. When a given location on the spherical Earth is in sunlight, its antipode – the location exactly on the opposite side of Earth – is in darkness. The spherical shape of Earth causes the Sun to rise and set at different times in ...
The curvature of the Earth is evident in the horizon across the image, and the bases of the buildings on the far shore are below that horizon and hidden by the sea. The simplest model for the shape of the entire Earth is a sphere. The Earth's radius is the distance from Earth's center to its surface, about 6,371 km (3,959 mi). While "radius ...
Topography globe featuring physical features of the Earth. A globe is a spherical model of Earth, of some other celestial body, or of the celestial sphere. Globes serve purposes similar to maps, but, unlike maps, they do not distort the surface that they portray except to scale it down. A model globe of Earth is called a terrestrial globe.
For example, the first evidence of knowledge of the spherical shape of Earth in Scandinavia is a 12th-century Old Icelandic translation of Elucidarius. [78] A list of more than a hundred Latin and vernacular writers from Late Antiquity and the Middle Ages who were aware that Earth was spherical has been compiled by Reinhard Krüger, professor ...
Spherical harmonics are often used to approximate the shape of the geoid. The current best such set of spherical harmonic coefficients is EGM2020 (Earth Gravitational Model 2020), determined in an international collaborative project led by the National Imagery and Mapping Agency (now the National Geospatial-Intelligence Agency, or NGA).
The Earth is not exactly spherical, mainly because of its rotation around the polar axis that makes its shape slightly oblate. However, a spherical harmonics series expansion captures the actual field with increasing fidelity. If Earth's shape were perfectly known together with the exact mass density ρ = ρ(x, y, z), it could be integrated ...
The Earth's shape deviates from spherical by flattening, but by only about 0.3%. Measurement of Earth's circumference has been important to navigation since ancient times. In modern times, Earth's circumference has been used to define fundamental units of measurement of length: the nautical mile in the seventeenth century and the metre in the ...