The flag of Goiás is formed of bars: the green bars symbolize spring and the yellow bars gold, just as in the national flag. The blue rectangle represents the sky and the stars are the constellation of the Southern Cross, chosen as the one which most typifies the sky of Goiás. The flag was created during the government of João Alves do Castro, governor of the state, through a law dated 30 July 1919, and was based on a design of Joaquim Bonifácio of Siqueira.
According to "Goiaz - Coração do Brasil" [Goiás: Heart of Brazil], by Ofélia Sócrates do Nascimento Monteiro, the flag was adopted by law no. 650 of 30 July 1919. The Southern Cross is identified with the original names given to Brazil by the first Portuguese explorers, Vera Cruz [True Cross] and Santa Cruz [Holy Cross]. Its appearance in the Goiás flag is also said to symbolize the beauty of the state's sky. Like other Brazilian state symbols, this flag would have been banned under the Vargas regime from 1937 to 1946. I do not have the citation of the legal act reinstating the flag, but a comparison with the one shown in Clovis Ribeiro's 1933 book of Brazilian flags shows it has not changed.
The green stripes represent the woods and forests of the state, while the yellow stripes symbolize the gold. The blue canton symbolizes the sky and the five stars represent the Southern Cross.