rubin_sim.skybrightness.zenith_twilight(alpha, *args)

The flux at zenith as a linear combination of a twilight component and a constant: alpha = sun altitude (radians) args[0] = ratio of (zenith twilight flux at sunAlt = -12) and dark sky zenith flux args[1] = decay slope for all pixels (mags/radian) args[2] = airmass term for hemisphere away from the sun. (factor to multiply max brightness at zenith by) args[3] = az term for hemisphere towards sun args[4] = zenith dark sky flux