The proposal for a Southern observatory in all likelihood originated among the same group of people who founded the
Royal Astronomical Society in the United Kingdom. The official establishment of the Royal Observatory, Cape of Good Hope occurred on 20 October 1820 Nevertheless, several telescopes remained in operation until the 1990s. These are rarely made use of today except for public outreach events.
Alan Cousins was the last serious observer to work from the Royal Observatory site. The Royal Observatory was responsible for a number of significant events in the history of astronomy. The second HM Astronomer,
Thomas Henderson, aided by his assistant, Lieutenant William Meadows, made the first observations that led to a believable stellar parallax, namely of
Alpha Centauri. However, he lost priority as the discoverer of
stellar parallax to
Friedrich Wilhelm Bessel, who published his own (later) observations of 61 Cygni before Henderson got around to his. Around 1840,
Thomas Maclear re-measured the controversial meridian of
Nicolas-Louis de La Caille, showing that the latter's geodetic measurements had been correct but that nearby mountains had affected his latitude determinations. In 1882,
David Gill obtained long-exposure photographs of the
great comet of that year showing the presence of stars in the background. This led him to undertake in collaboration with
J.C. Kapteyn of Groningen the Cape Photographic
Durchmusterung, the first stellar catalogue prepared by photographic means. In 1886, he proposed to
Admiral A.E.B. Mouchez of Paris Observatory the holding of an international congress to promote a photographic catalogue of the whole sky. In 1887 this congress took place in Paris and resulted in the
Carte du Ciel project. The Cape Observatory was assigned the zone between declinations −40° and −52°. The Carte du Ciel is regarded as the precursor of the
International Astronomical Union. In 1897 Frank McClean, a close friend of Gill's and the donor of the McClean telescope, discovered the presence of oxygen in a number of stars using an objective prism attached to the Astrographic Telescope. In 1911, J.K.E. Halm, then the Chief Assistant, put forward a pioneering paper on
stellar dynamics in which he hypothesized that the star streams discovered by Kapteyn arose from a
Maxwellian distribution of stellar velocities. This paper also contains the first suggestion that stars obey a mass-luminosity relationship. A later 20th-century HM Astronomer, H. Spencer Jones, was active in an international project for determining the solar parallax through observations of the minor planet
Eros. In the second half of the twentieth century Alan Cousins set up very precise southern standards for
UBV and introduced a widely used system of
VRI photometry that enjoyed international recognition for precision. In 1977 the occultation of the star SAO 158687 was observed by Joseph Churms from the former Royal Observatory, and these observations provided needed confirmation of the
Uranian rings discovered from the
Kuiper aeroplane by Elliot et al. During the 19th century the Observatory was regarded as the main advisor to the colonial government on scientific matters. it served as the repository for standard weights and measures of the Colony and was responsible for timekeeping and geodetic surveying. A magnetic observatory was constructed in 1841 but burned down during the following decade. The Observatory also possesses a long series of meteorological records. The history of the Royal Observatory has been the subject of several works. == Astronomers at the Cape ==