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Garai (astronomia).
Garaia, astronomian, koordenatuak emateko eta kalkulu zehatza emateko erabiltzen den denbora une zehatza da. Lurraren mugimendu batzuk nabarmenak dira (adibidez eguna edo urtea zehazten dituzten biraketak) baina beste batzuk ez hain nabarmenak, adibidez prezesioa eta nutazioa. Horregatik izarren koordenatuak aldatzen dira denboran zehar, nahiz eta oso nabarmena ez izan. Arrazoi hau dela eta behaketa eta neurketaren garaia zein den esatea komenigarria da.
Gaur egun egiten diren atlas gehienetan eta efemerideak ematen dituzten liburuetan J2000.0 da, 2000ko urtarrilak 1eko 12:00 UTCetan emana. J aurrizkiak garai juliarra dela esan nahi du. Lehenago erabiltzen zen estandarra B1950.0 zen, B horrek besseliar garaia zela adieraziz. 1984a baino lehen Besseliar garaiak erabiltzen ziren. Henry Draper katalogoak B1900.0 erabiltzen du eta konstelazioen mugak 1930an zehaztu zirenean B1875.0 erabili zuten.
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