# Union Observatory

Union Observatory, also known as Transvaal Observatory, Republic Observatory and Johannesburg Observatory (078), is a defunct astronomical observatory in Johannesburg, South Africa that operated from 1903 to 1971. It is located on Observatory Ridge, the city's highest point at 1,808 metres altitude in the suburb Observatory.
The observatory and its former annex, the § Leiden Southern Station, are known for the discovery of 6,000 double stars and for Proxima Centauri, made by astronomer Robert Innes. At the observatory, 578 identifications of minor planet were made, a record number at the time. The Minor Planet Center credits the observatory as the site where 147 minor planets were discovered by astronomers Harry Wood, Cyril Jackson, Hendrik van Gent, Ernest Johnson, Ejnar Hertzsprung, Jacobus Bruwer and Joseph Churms (see § List of discovered minor planets).

## History

The origins of the observatory began when Theodore Reunert of the South African Association for the Advancement of Science petitioned Alfred Milner Governor of the Transvaal Colony on 29 October 1902 for the establishment of a meteorological and astronomical observatory in Johannesburg.$^{:17}$ Assistant Colonial Secretary W.H. Moor agreed to the project on 17 December 1902 with the budget increased from £1,350 to £5,629 due to equipment changes.$^{:17}$
On 1 April 1903, a new Meteorological Department was temporarily established in Johannesburg.$^{:17}$ A location was sought for the new observatory and the Johannesburg Town Council made a decision on 12 May 1903, located within the municipal boundaries.$^{:17}$ The land of eight acres, on a ridge west of the Indian War Memorial, was on the northern boundary of the farm Doornfontein, presently part of the suburb Observatory and was given as a gift by the Bezuidenhout family, with a further two acres sold for £500.$^{:18}$ The land was given only for the use of science and a road, later called Observatory Avenue, was also to be built close to the site.$^{:18}$ The observatory building was built and the formal opening took place on 17 January 1905 by Governor Milner, but had no astronomical equipment.$^{:19}$
In 1906 it was lent a Hamberg universal instrument (2 5/8-inch object glass) by Dr Oskar Backlund.$^{:19}$ In September 1907 a 9-inch Grubb refractor was now used but repolished in 1908.$^{:19}$ Mr J. Franklin-Adams gifted the observatory a 10-inch triple O.G. Cooke Star-Camera in 1909.$^{:19}$ J.B. Rissik, Minister for Lands, permitted the purchase of a 26-inch refracting telescope from the Grubb Telescope Company in 1909.$^{:19}$
With the formation of the Union of South Africa in 1910, South Africa's two colonial observatories came under the control of the Minister of the Interior.$^{:19}$ With the removal of the meteorological functions, the observatory was renamed Observatory of the Union of South Africa (Union Observatory) on 1 April 1912.$^{:19}$ It became the Republic Observatory in 1961.
Well remembered for the quality of its Directors, work done on minor planets and the discovery of Proxima Centauri, growing light pollution problems in Johannesburg led to its closure in 1971–1972. The Observatory's buildings at 18a Gill Street, Observatory, Johannesburg, still exist.
At that time the South African government decided to amalgamate all astronomical research into one body, which later became known as the South African Astronomical Observatory (SAAO); it has its headquarters in Cape Town and has Sutherland as its outstation. The main Cape telescopes were moved to Sutherland, and the Radcliffe Observatory at Pretoria was also dismantled.
The main-belt asteroid 1585 Union, discovered by Ernest Johnson in 1947, was named for the Union observatory.

## Leiden Southern Station

The Leiden Southern Station (081) was a collaboration between the Dutch Leiden Observatory and Union Observatory. From 1938 to 1954 it was an annex to the Union Observatory, and was moved to Hartbeespoort in 1954 due to light pollution. It operated until 1978.

## Discoveries
### List of discovered minor planets

The Minor Planet Center credits Union Observatory ("Johannesburg"), as the site of 147 minor planet discoveries, made by the following list of astronomers:
* $^A$ Harry Edwin Wood
* $^B$ Cyril Jackson
* $^C$ Hendrik van Gent
* $^D$ Ernest Leonard Johnson
* $^E$ Ejnar Hertzsprung
* $^F$ Jacobus Albertus Bruwer
* $^G$ Joseph Churms
| important; height: 675px; |
| 715 Transvaalia | 22 April 1911 | list |
| 758 Mancunia | 18 May 1912 | list |
| 790 Pretoria | 16 January 1912 | list |
| 982 Franklina | 21 May 1922 | list |
| 1032 Pafuri | 30 May 1924 | list |
| 1096 Reunerta | 21 July 1928 | list |
| 1116 Catriona | 5 April 1929 | list |
| 1132 Hollandia | 13 September 1929 | list |
| 1133 Lugduna | 13 September 1929 | list |
| 1165 Imprinetta | 24 April 1930 | list |
| 1186 Turnera | 1 August 1929 | list |
| 1193 Africa | 24 April 1931 | list |
| 1194 Aletta | 13 May 1931 | list |
| 1195 Orangia | 24 May 1931 | list |
| 1196 Sheba | 21 May 1931 | list |
| 1197 Rhodesia | 9 June 1931 | list |
| 1225 Ariane | 23 April 1930 | list |
| 1226 Golia | 22 April 1930 | list |
| 1241 Dysona | 4 March 1932 | list |
| 1242 Zambesia | 28 April 1932 | list |
| 1243 Pamela | 7 May 1932 | list |
| 1244 Deira | 25 May 1932 | list |
| 1245 Calvinia | 26 May 1932 | list |
| 1246 Chaka | 23 July 1932 | list |
| 1248 Jugurtha | 1 September 1932 | list |
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| 1264 Letaba | 21 April 1933 | list |
| 1267 Geertruida | 23 April 1930 | list |
| 1268 Libya | 29 April 1930 | list |
| 1278 Kenya | 15 June 1933 | list |
| 1279 Uganda | 15 June 1933 | list |
| 1282 Utopia | 17 August 1933 | list |
| 1305 Pongola | 19 July 1928 | list |
| 1318 Nerina | 24 March 1934 | list |
| 1319 Disa | 19 March 1934 | list |
| 1320 Impala | 13 May 1934 | list |
| 1321 Majuba | 7 May 1934 | list |
| 1323 Tugela | 19 May 1934 | list |
| 1324 Knysna | 15 June 1934 | list |
| 1325 Inanda | 14 July 1934 | list |
| 1326 Losaka | 14 July 1934 | list |
| 1327 Namaqua | 7 September 1934 | list |
| 1336 Zeelandia | 9 September 1934 | list |
| 1337 Gerarda | 9 September 1934 | list |
| 1342 Brabantia | 13 February 1935 | list |
| 1349 Bechuana | 13 June 1934 | list |
| 1353 Maartje | 13 February 1935 | list |
| 1354 Botha | 3 April 1935 | list |
| 1355 Magoeba | 30 April 1935 | list |
| 1356 Nyanza | 3 May 1935 | list |
| 1357 Khama | 2 July 1935 | list |
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| 1358 Gaika | 21 July 1935 | list |
| 1359 Prieska | 22 July 1935 | list |
| 1360 Tarka | 22 July 1935 | list |
| 1362 Griqua | 31 July 1935 | list |
| 1367 Nongoma | 3 July 1934 | list |
| 1368 Numidia | 30 April 1935 | list |
| 1383 Limburgia | 9 September 1934 | list |
| 1384 Kniertje | 9 September 1934 | list |
| 1385 Gelria | 24 May 1935 | list |
| 1389 Onnie | 28 September 1935 | list |
| 1393 Sofala | 25 May 1936 | list |
| 1394 Algoa | 12 June 1936 | list |
| 1396 Outeniqua | 9 August 1936 | list |
| 1397 Umtata | 9 August 1936 | list |
| 1427 Ruvuma | 16 May 1937 | list |
| 1428 Mombasa | 5 July 1937 | list |
| 1429 Pemba | 2 July 1937 | list |
| 1430 Somalia | 5 July 1937 | list |
| 1431 Luanda | 29 July 1937 | list |
| 1432 Ethiopia | 1 August 1937 | list |
| 1456 Saldanha | 2 July 1937 | list |
| 1467 Mashona | 30 July 1938 | list |
| 1468 Zomba | 23 July 1938 | list |
| 1474 Beira | 20 August 1935 | list |
| 1490 Limpopo | 14 June 1936 | list |
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| 1505 Koranna | 21 April 1939 | list |
| 1506 Xosa | 15 May 1939 | list |
| 1568 Aisleen | 21 August 1946 | list |
| 1580 Betulia | 22 May 1950 | list |
| 1585 Union | 7 September 1947 | list |
| 1595 Tanga | 19 June 1930 | list |
| 1607 Mavis | 3 September 1950 | list |
| 1609 Brenda | 10 July 1951 | list |
| 1618 Dawn | 5 July 1948 | list |
| 1623 Vivian | 9 August 1948 | list |
| 1627 Ivar | 25 September 1929 | list |
| 1634 Ndola | 19 August 1935 | list |
| 1638 Ruanda | 3 May 1935 | list |
| 1641 Tana | 25 July 1935 | list |
| 1658 Innes | 13 July 1953 | list |
| 1660 Wood | 7 April 1953 | list |
| 1663 van den Bos | 4 August 1926 | list |
| 1666 van Gent | 22 July 1930 | list |
| 1667 Pels | 16 September 1930 | list |
| 1670 Minnaert | 9 September 1934 | list |
| 1676 Kariba | 15 June 1939 | list |
| 1686 De Sitter | 28 September 1935 | list |
| 1689 Floris-Jan | 16 September 1930 | list |
| 1693 Hertzsprung | 5 May 1935 | list |
| 1694 Kaiser | 29 September 1934 | list |
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| 1701 Okavango | 6 July 1953 | list |
| 1702 Kalahari | 7 July 1924 | list |
| 1712 Angola | 28 May 1935 | list |
| 1731 Smuts | 9 August 1948 | list |
| 1738 Oosterhoff | 16 September 1930 | list |
| 1752 van Herk | 22 July 1930 | list |
| 1753 Mieke | 10 May 1934 | list |
| 1760 Sandra | 10 April 1950 | list |
| 1784 Benguella | 30 June 1935 | list |
| 1816 Liberia | 29 January 1936 | list |
| 1817 Katanga | 20 June 1939 | list |
| 1819 Laputa | 9 August 1948 | list |
| 1879 Broederstroom | 16 October 1935 | list |
| 1885 Herero | 9 August 1948 | list |
| 1914 Hartbeespoortdam | 28 September 1930 | list |
| 1922 Zulu | 25 April 1949 | list |
| 1925 Franklin-Adams | 9 September 1934 | list |
| 1945 Wesselink | 22 July 1930 | list |
| 1946 Walraven | 8 August 1931 | list |
| 1948 Kampala | 3 April 1935 | list |
| 1949 Messina | 8 July 1936 | list |
| 1986 Plaut | 28 September 1935 | list |
| 2019 van Albada | 28 September 1935 | list |
| 2025 Nortia | 6 June 1953 | list |
| 2066 Palala | 4 June 1934 | list |
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| 2193 Jackson | 18 May 1926 | list |
| 2203 van Rhijn | 28 September 1935 | list |
| 2378 Pannekoek | 13 February 1935 | list |
| 2546 Libitina | 23 March 1950 | list |
| 2651 Karen | 28 August 1949 | list |
| 2718 Handley | 30 July 1951 | list |
| 2801 Huygens | 28 September 1935 | list |
| 2825 Crosby | 19 September 1938 | list |
| 2829 Bobhope | 9 August 1948 | list |
| 2831 Stevin | 17 September 1930 | list |
| 2865 Laurel | 31 July 1935 | list |
| 2945 Zanstra | 28 September 1935 | list |
| 3184 Raab | 22 August 1949 | list |
| 3284 Niebuhr | 13 July 1953 | list |
| 3300 McGlasson | 10 July 1928 | list |
| 3768 Monroe | 5 September 1937 | list |
| 4296 van Woerkom | 28 September 1935 | list |
| 4359 Berlage | 28 September 1935 | list |
| 4511 Rembrandt | 28 September 1935 | list |
| 5038 Overbeek | 31 May 1948 | list |
| (5452) 1937 NN | 5 July 1937 | list |
| 7102 Neilbone | 12 July 1936 | list |