Converts calendar day into true solar longitude for a given astronomical configuration and vice-versa
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Output from a solution, such as
true solar longitude, in radiants
calendar day, in a 360-d year
The 360-d calendar is a conventional calendar, for which day 80 is the day of NH spring equinoxe. The tropic year, which in reality is 365.24219876 * 86400 seconds was the practical reference to define the Gregorian Calendar since this is the time needed to go through all the seasons. More discussion of calendars and conversions in Berger et al. (2010) appendix D.
l2day is based on algoritms
given in Berger (1978), but which can be traced back to
expansions of the mean and true anomaly by Brouwer and Clemente (1961),
pp. 65 and 77 (see code for further details).
day of year (360-d cal.) or true solar longitude (in radiants).
Michel Crucifix, U. catholique de Louvain, Belgium.
Brouwer D. and G. M. Clemence, (1961), Methods of celestial mechanics, Academic Press, New York.
Berger, (1978) Long-term variations of daily insolation and Quaternary climatic changes, J. Atmos. Sci., 35, 2362-2367 1978, doi:10.1175/1520-0469(1978)035<2362:LTVODI>2.0.CO;2
Berger, A. Loutre, M.F. and Yin Q. (2010), Total irradiation during any time interval of the year using elliptic integrals, Quaternary Science Reviews, 29, 1968 - 1982, doi:10.1016/j.quascirev.2010.05.007
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