I used to think that a flower blooms once the petals open up, but since a sunflower is a composite flower, the process is a bit different.
To refresh your memory: composite flowers are made up of the ray and disc flowers. The ray flower is made up of the outer petals – what we ordinarily consider regular petals – and the disc flowers are the cluster of flowers in the middle of the flower – generally speaking, of course.
And, yes, to my great enlightenment, there are disc flowers on sunflowers! I’d never thought about it, nor really looked up the nitty-gritty about sunflowers. As you should know, my normal modus operandi is to get seeds, plant them and have my happy surprises along the way. So I did indeed enjoy watching the sunflowers bloom.