Since antiquity the arcminute and arcsecond have been used in astronomy. In the ecliptic coordinate system, latitude (β) and longitude (λ); in the horizon system, altitude (Alt) and azimuth (Az); and in the equatorial coordinate system, declination (δ), are all measured in degrees, arcminutes and arcseconds. The principal exception is Right ascension (RA) in equatorial coordinates, which is measured in time units of hours, minutes, and seconds.