def solar_position(moment, latitude, longitude, Z=0.0, T=298.15, P=101325.0, 
                           atmos_refract=0.5667):
    r'''Calculate the position of the sun in the sky. It is defined in terms of
    two angles - the zenith and the azimith. The azimuth tells where a sundial
    would see the sun as coming from; the zenith tells how high in the sky it
    is. The solar elevation angle is returned for convinience; it is the 
    complimentary angle of the zenith.
    
    The sun's refraction changes how high it appears as though the sun is;
    so values are returned with an optional conversion to the aparent angle.
    This impacts only the zenith/elevation.
    
    Uses the Reda and Andreas (2004) model described in [1]_, 
    originally incorporated into the excellent 
    `pvlib library <https://github.com/pvlib/pvlib-python>`_    
    
    Parameters
    ----------
    moment : datetime
        Time and date for the calculation, in local UTC time (not daylight 
        savings time), [-]
    latitude : float
        Latitude, between -90 and 90 [degrees]
    longitude : float
        Longitude, between -180 and 180, [degrees]
    Z : float, optional
        Elevation above sea level for the solar position calculation, [m]
    T : float, optional
        Temperature of atmosphere at ground level, [K]
    P : float, optional
        Pressure of atmosphere at ground level, [Pa]
    atmos_refract : float, optional
        Atmospheric refractivity, [degrees]

    Returns
    -------
    apparent_zenith : float
        Zenith of the sun as observed from the ground based after accounting
        for atmospheric refraction, [degrees]
    zenith : float
        Actual zenith of the sun (ignores atmospheric refraction), [degrees]
    apparent_altitude : float
        Altitude of the sun as observed from the ground based after accounting
        for atmospheric refraction, [degrees]
    altitude : float
        Actual altitude of the sun (ignores atmospheric refraction), [degrees]
    azimuth : float
        The azimuth of the sun, [degrees]
    equation_of_time : float
        Equation of time - the number of seconds to be added to the day's
        mean solar time to obtain the apparent solar noon time, [seconds]

    Examples
    --------
    >>> solar_position(datetime(2003, 10, 17, 13, 30, 30), 45, 45)
    [140.8367913391112, 140.8367913391112, -50.83679133911118, -50.83679133911118, 329.9096671679604, 878.4902950980904]

    Sunrise occurs when the zenith is 90 degrees (Calgary, AB):
    
    >>> solar_position(datetime(2018, 4, 15, 6, 43, 5), 51.0486, -114.07)[0]
    90.00054676987014
    
    Sunrise also occurs when the zenith is 90 degrees (13.5 hours later):
        
    >>> solar_position(datetime(2018, 4, 15, 20, 30, 28), 51.0486, -114.07)
    [89.9995695661236, 90.54103812161853, 0.00043043387640950836, -0.5410381216185247, 286.8313781904518, 6.631429525878048]
    
    Notes
    -----    
    If you were standing at the same longitude of the sun such that it was no
    further east or west than you were, the amount of angle it was south or 
    north of you is the *zenith*. If it were directly overhead it would be 0°;
    a little north or south and it would be a little positive;
    near sunset or sunrise, near 90°; and at night, between 90° and 180°.
    
    The *solar altitude angle* is defined as 90° -`zenith`.
    Note the *elevation* angle is just another name for the *altitude* angle.
    
    The *azimuth* the angle in degrees that the sun is East of the North angle.
    It is positive North eastwards 0° to 360°. Other conventions may be used.
    
    Note that due to differences in atmospheric refractivity, estimation of
    sunset and sunrise are accuract to no more than one minute. Refraction
    conditions truly vary across the atmosphere; so characterizing it by an
    average value is limiting as well.

    References
    ----------
    .. [1] Reda, Ibrahim, and Afshin Andreas. "Solar Position Algorithm for 
       Solar Radiation Applications." Solar Energy 76, no. 5 (January 1, 2004):
       577-89. https://doi.org/10.1016/j.solener.2003.12.003.
    .. [2] "Navigation - What Azimuth Description Systems Are in Use? - 
       Astronomy Stack Exchange." 
       https://astronomy.stackexchange.com/questions/237/what-azimuth-description-systems-are-in-use?rq=1.
    '''
    from fluids.optional import spa
    delta_t = spa.calculate_deltat(moment.year, moment.month)
    unixtime = time.mktime(moment.timetuple())    
    # Input pressure in milibar; input temperature in deg C
    result = spa.solar_position_numpy(unixtime, lat=latitude, lon=longitude, elev=Z, 
                          pressure=P*1E-2, temp=T-273.15, delta_t=delta_t,
                          atmos_refract=atmos_refract, sst=False, esd=False)
    # confirmed equation of time https://www.minasi.com/figeot.asp
    # Convert minutes to seconds; sometimes negative, sometimes positive

    result[-1] = result[-1]*60.0 
    return result
r'''Calculate the position of the sun in the sky. It is defined in terms of
    two angles - the zenith and the azimith. The azimuth tells where a sundial
    would see the sun as coming from; the zenith tells how high in the sky it
    is. The solar elevation angle is returned for convinience; it is the 
    complimentary angle of the zenith.
    
    The sun's refraction changes how high it appears as though the sun is;
    so values are returned with an optional conversion to the aparent angle.
    This impacts only the zenith/elevation.
    
    Uses the Reda and Andreas (2004) model described in [1]_, 
    originally incorporated into the excellent 
    `pvlib library <https://github.com/pvlib/pvlib-python>`_    
    
    Parameters
    ----------
    moment : datetime
        Time and date for the calculation, in local UTC time (not daylight 
        savings time), [-]
    latitude : float
        Latitude, between -90 and 90 [degrees]
    longitude : float
        Longitude, between -180 and 180, [degrees]
    Z : float, optional
        Elevation above sea level for the solar position calculation, [m]
    T : float, optional
        Temperature of atmosphere at ground level, [K]
    P : float, optional
        Pressure of atmosphere at ground level, [Pa]
    atmos_refract : float, optional
        Atmospheric refractivity, [degrees]

    Returns
    -------
    apparent_zenith : float
        Zenith of the sun as observed from the ground based after accounting
        for atmospheric refraction, [degrees]
    zenith : float
        Actual zenith of the sun (ignores atmospheric refraction), [degrees]
    apparent_altitude : float
        Altitude of the sun as observed from the ground based after accounting
        for atmospheric refraction, [degrees]
    altitude : float
        Actual altitude of the sun (ignores atmospheric refraction), [degrees]
    azimuth : float
        The azimuth of the sun, [degrees]
    equation_of_time : float
        Equation of time - the number of seconds to be added to the day's
        mean solar time to obtain the apparent solar noon time, [seconds]

    Examples
    --------
    >>> solar_position(datetime(2003, 10, 17, 13, 30, 30), 45, 45)
    [140.8367913391112, 140.8367913391112, -50.83679133911118, -50.83679133911118, 329.9096671679604, 878.4902950980904]

    Sunrise occurs when the zenith is 90 degrees (Calgary, AB):
    
    >>> solar_position(datetime(2018, 4, 15, 6, 43, 5), 51.0486, -114.07)[0]
    90.00054676987014
    
    Sunrise also occurs when the zenith is 90 degrees (13.5 hours later):
        
    >>> solar_position(datetime(2018, 4, 15, 20, 30, 28), 51.0486, -114.07)
    [89.9995695661236, 90.54103812161853, 0.00043043387640950836, -0.5410381216185247, 286.8313781904518, 6.631429525878048]
    
    Notes
    -----    
    If you were standing at the same longitude of the sun such that it was no
    further east or west than you were, the amount of angle it was south or 
    north of you is the *zenith*. If it were directly overhead it would be 0°;
    a little north or south and it would be a little positive;
    near sunset or sunrise, near 90°; and at night, between 90° and 180°.
    
    The *solar altitude angle* is defined as 90° -`zenith`.
    Note the *elevation* angle is just another name for the *altitude* angle.
    
    The *azimuth* the angle in degrees that the sun is East of the North angle.
    It is positive North eastwards 0° to 360°. Other conventions may be used.
    
    Note that due to differences in atmospheric refractivity, estimation of
    sunset and sunrise are accuract to no more than one minute. Refraction
    conditions truly vary across the atmosphere; so characterizing it by an
    average value is limiting as well.

    References
    ----------
    .. [1] Reda, Ibrahim, and Afshin Andreas. "Solar Position Algorithm for 
       Solar Radiation Applications." Solar Energy 76, no. 5 (January 1, 2004):
       577-89. https://doi.org/10.1016/j.solener.2003.12.003.
    .. [2] "Navigation - What Azimuth Description Systems Are in Use? - 
       Astronomy Stack Exchange." 
       https://astronomy.stackexchange.com/questions/237/what-azimuth-description-systems-are-in-use?rq=1.