John Herschel discovers the open cluster NGC 3603

Background. Sir John Frederick William Herschel, an English polymath and astronomer, departed Portsmouth on 13 November 1833 with his wife, their three children and his 20 inch telescope. He arrived in Cape Town on 15 January 1834 and set up a private 21 ft (6.4 m) telescope at Feldhausen, an old estate on the south-eastern side of Table Mountain in Claremont, a suburb of Cape Town, where the family made their home during their stay.

Observation. On 14 March 1834, Herschel observed NGC 3603 during his visit to South Africa. He remarked that it was "a very remarkable object...perhaps a globular cluster." This observation was part of his broader telescopic survey of the visible heavens, which he conducted from the Cape of Good Hope between 1834 and 1838.

Classification. While Herschel initially suspected NGC 3603 was a globular cluster, modern analysis identifies it as a massive H II region. It contains a very compact open cluster, likely a super star cluster designated HD 97950. This distinction highlights the evolution of astronomical classification from Herschel's initial visual assessment.