daylength: Length of daylight
In insol: Solar Radiation

Description Usage Arguments Details Value Note Author(s) References See Also Examples

Compute duration of day light for a given latitude and Julian Day.

1	daylength(lat, long, jd, tmz)

`lat`	Latitude in degrees and decimal fraction.
`long`	Longitude in degrees and decimal fraction.
`jd`	Julian Day.
`tmz`	Timezone, west of Greenwich is negative.

It considers sunrise and sunset as the time when the center of the sun pass above or below the horizon, it does not take into account limb, summer time, atmospheric refraction or twilight.

`sunrise`	Time of sunrise.
`sunset`	Time of sunset.
`daylen`	Duration of daylight in hours and decimal fraction.

It returns NA for sunrise and sunset during the polar night.

You may like to double check at: https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html

Javier G. Corripio

Corripio, J. G.: 2003, Vectorial algebra algorithms for calculating terrain parameters from DEMs and the position of the sun for solar radiation modelling in mountainous terrain, International Journal of Geographical Information Science 17(1), 1-23.

declination, eqtime

daylength(47,11,JDymd(2019,1,1,12),1)
daylength(c(47,75),11,2456282,1)

# Daylength for the whole 2019 year
jd2019=JD(seq(ISOdate(2019,1,1),ISOdate(2019,12,31),by='day'))
plot(daylength(47,11,jd2019,1)[,3],xlab='Day of the year',ylab='day length [h]',ylim=c(0,24))