def earthsun_distance(moment):
r'''Calculates the distance between the earth and the sun as a function
of date and time. 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 UTC time (or GMT, which is
almost the same thing); not local time, [-]
Returns
-------
distance : float
Distance between the center of the earth and the center of the sun,
[m]
Examples
--------
>>> earthsun_distance(datetime(2003, 10, 17, 13, 30, 30))
149090925951.18338
The distance at perihelion, which occurs at 4:21 according to this
algorithm. The real value is 04:38 (January 2nd).
>>> earthsun_distance(datetime(2013, 1, 2, 4, 21, 50))
147098089490.67123
The distance at aphelion, which occurs at 14:44 according to this
algorithm. The real value is dead on - 14:44 (July 5).
>>> earthsun_distance(datetime(2013, 7, 5, 14, 44, 51, 0))
152097354414.36044
Notes
-----
This function is quite accurate. The difference comes from the impact of
the moon.
Note this function is not continuous; the sun-earth distance is not
sufficiently accurately modeled for the change to be continuous throughout
each day.
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.
'''
from fluids.optional import spa
delta_t = spa.calculate_deltat(moment.year, moment.month)
import calendar
unixtime = calendar.timegm(moment.timetuple())
# Convert datetime object to unixtime
return float(spa.earthsun_distance(unixtime, delta_t=delta_t)) * au
def earthsun_distance(moment):
r'''Calculates the distance between the earth and the sun as a function
of date and time. 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 UTC time (or GMT, which is
almost the same thing); not local time, [-]
Returns
-------
distance : float
Distance between the center of the earth and the center of the sun,
[m]
Examples
--------
>>> earthsun_distance(datetime(2003, 10, 17, 13, 30, 30))
149090925951.18338
The distance at perihelion, which occurs at 4:21 according to this
algorithm. The real value is 04:38 (January 2nd).
>>> earthsun_distance(datetime(2013, 1, 2, 4, 21, 50))
147098089490.67123
The distance at aphelion, which occurs at 14:44 according to this
algorithm. The real value is dead on - 14:44 (July 5).
>>> earthsun_distance(datetime(2013, 7, 5, 14, 44, 51, 0))
152097354414.36044
Notes
-----
This function is quite accurate. The difference comes from the impact of
the moon.
Note this function is not continuous; the sun-earth distance is not
sufficiently accurately modeled for the change to be continuous throughout
each day.
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.
'''
from fluids.optional import spa
delta_t = spa.calculate_deltat(moment.year, moment.month)
import calendar
unixtime = calendar.timegm(moment.timetuple())
# Convert datetime object to unixtime
return float(spa.earthsun_distance(unixtime, delta_t=delta_t))*au