Union Observatory

thumb|Photo of comet Mellish obtained with the Franklin Adams star camera of the Union Observatory on June 6, 1915, with an exposure of ninety minutes. The position of the comet was then [[Right ascension|R.A. 22h. 35m., declination 70° 18′ south.]]

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. 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.

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