Altazimuth telescope at the Royal Observatory, Greenwich, London, England. This altazimuth telescope was constructed at Greenwich in the nineteenth century by the British astronomer George Biddell Airy (1801-1892). An altazimuth is used to measure the altitude (from the horizon) and azimuth (angle from north) of a star. These measurements can then be used to calculate the precise position of the star. Unlike a transit circle telescope, an altazimuth telescope can be pointed at any region of the sky, using a complicated mechanism to move the telescope. Artwork published in the autobiography of the British astronomer Edwin Dunkin, who worked at Greenwich.