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An armillary sphere is a model of objects in the sky (in the celestial sphere), consisting of a spherical framework of rings, centred on Earth, that represent lines of celestial longitude and latitude and other astronomically important features such as the ecliptic.
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Palau issued an exceptional pair of coins, celebrating the 400 years of telescopes in 2008.
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The meridians are important parts of the terrestrial navigation. Before the era of GPS satellites the only method to determine the longitude of a place on the Earth was the measure of longitude (and lattitude) by astronomical methods. For these measurement the so called transit equipments, the passage instruments were used. Both meridians and the instruments used to measured them can be found on medals and coins.