rubin_sim.skybrightness.twilight_func(xdata, *args, amCut=1.0)

xdata: numpy array with columns ‘alt’, ‘az’, ‘sunAlt’ all in radians. az should be relative to the sun (i.e., sun is at az zero.

based on what I’ve seen, here’s my guess for how to fit the twilight: args[0] = ratio of (zenith twilight flux at sun_alt = -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 args[5:] = zenith dark sky times constant (optionall)

amCutfloat (1.0)

The airmass cut to apply to use only the away from sun fit. Was set to 1.1 previously for not very clear reasons.