Main-belt asteroid (6478) Gault unexpectedly sprouted two tails in late 2018 and early 2019, identifying it as a new active asteroid. Here we present observations obtained by the 1.2 m Zwicky Transient Facility survey telescope that provide detailed time-series coverage of the onset and evolution of Gault's activity. Gault exhibited two brightening events, with the first one starting on 2018 October 18 ±5 days and a second one starting on 2018 December 24 ±1 days. The amounts of mass released are 2 ×10 7 kg and 1 ×10 6 kg, respectively. Based on photometric measurements, each event persisted for about a month.
- comets: individual ((6478) Gault)
- minor planets, asteroids: individual ((6478) Gault)