def calc_sky_temperature(horiz_ir, source_emissivity=<NUM_LIT:1>):
sigma = <NUM_LIT>  <EOL>return ((horiz_ir / (source_emissivity * sigma)) ** <NUM_LIT>) - <NUM_LIT><EOL>
Calculate sky temperature in Celcius.

    See EnergyPlus Enrineering Reference for more information:
    https://bigladdersoftware.com/epx/docs/8-9/engineering-reference/
    climate-calculations.html#energyplus-sky-temperature-calculation

    Args:
        horiz_ir: A float value that represents horizontal infrared radiation
            intensity in W/m2.
        source_emissivity: A float value between 0 and 1 indicating the emissivity
             of the heat source that is radiating to the sky. Default is 1 for
             most outdoor surfaces.

    Returns:
        sky_temp: A sky temperature value in C.