import math


def calc_ssp_dist(lon, lat):
    """
    Eq. 4.5
    Calculates the geostationary satellite's Satellite Sub Point (SSP) distance
    ange (ups) for a given longitude & latitude

    Parameters
    ------------
    lon : float
        Longitude coordinate, in decimal degrees

    lat : float
        Latitude coordinate, in decimal degrees

    Returns
    ------------
    ups: float
        The SSP distance angle for the given longitude & latitude coordinates,
        in degrees
    """
    cos_ups = math.cos(math.radians(lon)) + math.cos(math.radians(lat))
    ups = math.acos(math.radians(cos_ups))
    return math.degrees(ups)