Due to a scheduling change, which tennis Grand Slam was held twice in 1977?

The Australian Open is a major tennis tournament held annually over the last fortnight of January in Melbourne, Australia. First held in 1905, the tournament is chronologically the first of the four Grand Slam tennis events of the year – the other three being the French Open, Wimbledon and the US Open.

Before the Melbourne Park stadium era, tournament dates fluctuated as well, in particular in the early years because of the climate of each site or exceptional events. For example, the 1919 tournament was held in January 1920 (the 1920 tournament was played in March) and the 1923 tournament in Brisbane took place in August when the weather was not too hot and wet.

The 1977 Australian Open (January) was a tennis tournament played on outdoor grass courts at the Kooyong Stadium in Melbourne, Australia. The tournament was held from 3 to 9 January 1977. Due to a scheduling change two Australian Opens took place in 1977 with the second taking place from 19 to 31 December 1977.