Astronomer Royal is a senior post in the Royal Households of the United Kingdom. There are two officers, the senior being the Astronomer Royal dating from 22 June 1675; the junior is the Astronomer Royal for Scotland dating from 1834.

The Astronomer Royal works to make observations to improve navigation, cartography, instrument design, and applications of geomagnetism. The position was created with the overall goal of discovering a way to determine longitude at sea when out of sight of land. The incumbent Astronomer Royal is Professor Michele Dougherty.

The post was created by Charles II in 1675, at the same time as he founded the Royal Observatory, Greenwich. He appointed John Flamsteed, instructing him "forthwith to apply himself with the most exact care and diligence to the rectifying the tables of the motions of the heavens, and the places of the fixed stars, so as to find out the so-much desired longitude of places, for the perfecting the art of navigation." The first six Astronomers Royal dedicated themselves primarily to this task and focused on astronomical observations that would benefit navigation.

The astronomer royal was director of the Royal Observatory, Greenwich from the establishment of the post in 1675 until 1972. The astronomer royal became an honorary title in 1972 without executive responsibilities, and a separate post of director of the Royal Greenwich Observatory was created to manage the institution.

The origin of the title Astronomer Royal is unknown. Although Flamsteed is widely considered the first Astronomer Royal, he was never appointed with the title and only referred to in the Warrant to Ordinance as "Our Astronomical Observer". Similar language was used to appoint all the Astronomers Royal until 1881 with William Christie's appointment. The term Astronomer Royal did not become commonly used until the late 18th Century while the Royal Warrants still used "Our Astronomical Observer". Other titles such as Royal Professor at Greenwich were also used in less formal documents during this time.

In 1703, Isaac Newton was elected President of the Royal Society, and was upset with the lack of publications coming from the Greenwich Observatory under Flamsteed. This eventually led to Queen Anne's Warrant of 1710 where members of the Royal Society were appointed as the Board of Visitors to the Royal Observatory to oversee Flamsteed. The original Board of Visitors consisted entirely of associates and allies of Newton, which enraged Flamsteed.

In 1765, the Board of Longitude decided that the Astronomer Royal's observations were the property of the Crown and must be printed and published each year. John Pond and subsequent Astronomers Royal elected to publish their findings quarterly instead.

Sir George Airy transformed the position from its original purpose of improving navigation to conducting more general astronomical and scientific research. With approval from the Board of Visitors in 1836, Airy created a Magnetic and Meteorological Department in the Royal Observatory Greenwich. Following this, in 1873 he created the Solar Photography Department.