Find the domain of the function

f(x,y) = arcsin(x^2+y^2-2)

From what I've seen in an example problem arcsin(x^2+y^2-2) must be greater than 0 (not sure why this is) but I don't know for what values arcsin > 0 since it's a trig function that has positive and negative values...if someone could help, it would be greatly appreciated.