day2l | R Documentation |
Converts calendar day into true solar longitude for a given astronomical configuration and vice-versa
day2l(orbit, day)
l2day(orbit, l)
date_of_perihelion(orbit)
orbit |
Output from a solution, such as |
day |
calendar day, in a 360-d year |
l |
true solar longitude, in radians |
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).
day of year (360-d cal.) or true solar longitude (in radians).
l2day()
: Converts true solar longitude into calendar day
date_of_perihelion()
: Returns date of perihelion
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
## 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.)
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