Output from a solution, such as ber78, ber90 or la04
l
true solar longitude, in radiants
day
calendar day, in a 360-d year
Details
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.
The day2l and 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).
Value
day of year (360-d cal.) or true solar longitude (in radiants).
Author(s)
Michel Crucifix, U. catholique de Louvain, Belgium.
References
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
Examples
## date of perihelion throughout today
orbit=c(eps=0.409214, ecc=0.01672393, varpi=4.92251)
date_of_perihelion(orbit)
## date of winter solstice)
l2day(orbit, 270*pi/180.)