A globe is a three-dimensional scale model of Earth (terrestrial globe) or other spheroid celestial body such as a planet, star, or moon. It may also refer to a spherical representation of the celestial sphere, showing the apparent positions of the stars and constellations in the sky (celestial globe). The word "globe" comes from the Latin word globus, meaning round mass or sphere.
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A globe is the only representation of the earth that does not distort either the shape or the size of large features; flat maps are created using a map projection that inevitably introduces an increasing amount of distortion the larger the area that the map shows. A typical scale for a terrestrial globe is roughly 1:40 million.
Sometimes a globe has surface texture showing topography; in these, elevations are exaggerated, otherwise they would be hardly visible. Most modern globes are also imprinted with parallels and meridians, so that one can tell the approximate coordinates of a specific place. Globes provide the best view of Earth today.
Celestial globes show the apparent positions of the stars in the sky. They omit the Sun, Moon and planets because the positions of these bodies vary relative to those of the stars, but the ecliptic, along which the Sun moves, is indicated.
A potential issue arises regarding the "handedness" of celestial globes. If the globe is constructed so that the stars are in the positions they actually occupy on the imaginary celestial sphere, then the star field will appear back-to-front on the surface of the globe (all the constellations will appear as their mirror images). This is because the view from Earth, positioned at the centre of the celestial sphere, is of the inside of the celestial sphere, whereas the celestial globe is viewed from the outside. For this reason, celestial globes may be produced in mirror image, so that at least the constellations appear the "right way round". Some modern celestial globes address this problem by making the surface of the globe transparent. The stars can then be placed in their proper positions and viewed through the globe, so that the view is of the inside of the celestial sphere, as it is from Earth.
The sphericity of the Earth was established by Hellenistic astronomy in the 3rd century BC, and the earliest terrestrial globe appeared from that period. The earliest known example is the one constructed by Crates of Mallus in Cilicia (now Çukurova in modern-day Turkey), in the mid-2nd century BC.[1]
No terrestrial globes from Antiquity or the Middle Ages have survived. An example of a surviving celestial globe is part of a Hellenistic sculpture, called the Farnese Atlas, surviving in a 2nd century AD Roman copy in the Naples Museum, Italy.[2]
Early terrestrial globes depicting the entirety of the Old World were constructed in the Islamic Golden Age. One such example was constructed in the 9th century by Muslim geographers and cartographers working under the Abbasid caliph, Al-Ma'mun.[3][4] Another example was the terrestrial globe introduced to Beijing by the Persian astronomer, Jamal ad-Din, in 1267.[5]
The oldest surviving terrestrial globe is the Erdapfel, created by Martin Behaim in Nuremberg, Germany, in 1492.[2] A facsimile globe showing America was made by Martin Waldseemueller in 1507. Another early globe, the Hunt-Lenox Globe, ca. 1507, is thought to be the source of the phrase "Here be dragons". Another "remarkably modern-looking" terrestrial globe of the Earth was constructed by Taqi al-Din at the Istanbul observatory of Taqi al-Din during the 1570s.[6]
An unusually high proportion of vintage 20th century world globes feature the Australian town of Birdum, which no longer exists but once held an important position at the end of the Northern Australian Railway.
Globus IMP electro-mechanical devices including five-inch globes have been used in Soviet and Russian spacecraft from 1961 to 2002 as navigation instruments. In 2001, the TMA version of the Soyuz spacecraft replaced this instrument with a virtual globe.[7]
Traditionally, globes were manufactured by gluing a printed paper map onto a sphere, often made from wood.
The most common type has long, thin gores (strips) of paper that narrow to a point at the poles,[8] small disks cover over the inevitable irregularities at these points. The more gores there are, the less stretching and crumpling is required to make the paper map fit the sphere. From a geometric point of view, all points on a sphere are equivalent – one could select any arbitrary point on the Earth, and create a paper map that covers the Earth with strips that come together at that point and the antipodal point.
Modern globes are often made from thermoplastic. Flat, plastic disks are printed with a distorted map of one of the Earth's Hemispheres. This is placed in machine which molds the disk into a hemispherical shape. The hemisphere is united with it's opposite counterpart to form a complete globe.
A globe is usually mounted at a 23.5° angle on bearings. In addition to making it easy to use this mounting also represents the angle of the planet in relation to its sun and the spin of the planet. This makes it easy to visualize how days and seasons change.
