These factors vary with atmospheric composition, geographic location, and time (see position of the Sun).
ðiːz fˈæktɚz vˈɛɹi wɪð ˌætməsfˈɛɹɪk kˌɑːmpəzˈɪʃən, dʒˌɪəɡɹˈæfɪk loʊkˈeɪʃən, ænd tˈaɪm sˈiː pəzˈɪʃən ʌvðə sˈʌn.