Resetting an objects center of rotation

Hello, Often when i modelling an objects center of rotation (well thats what i am calling it here as i dont know the proper name) appears way outside the object this is irratating if i am trying to rotate it or scale it

Thats an example the white dot is the problem i think

Is there anyway to make that white dot appear inside the object?

Thankyou in advance

Brillant Thankyou so much =D