suncalc

R implementation for calculating sun position, sunlight phases (times for sunrise, sunset, dusk, etc.), moon position and lunar phase for the given location and time. Most calculations are based on the formulas given in Astronomy Answers articles about position of the sun and the planets : https://www.aa.quae.nl/en/reken/zonpositie.html

News

0.5.0 dev version

• fully recode in R rather than call suncalc.js, so up to 500x faster...!

Installation

# from cran
install.packages("suncalc")
devtools::install_github("datastorm-open/suncalc") for developpement version

Use

require(suncalc)
?getSunlightTimes
getSunlightTimes(date = Sys.Date(), lat = 50.1, lon = 1.83, tz = "CET")

About suncalc

Most calculations are based on the formulas given in the excellent Astronomy Answers articles about position of the sun and the planets. You can read about different twilight phases calculated by SunCalc in the Twilight article on Wikipedia.

Reference

Sunlight times

Returns an object with the following properties (each is a Date object):

Sun position

Returns an object with the following properties:

• altitude: sun altitude above the horizon in radians, e.g. 0 at the horizon and PI/2 at the zenith (straight over your head)
• azimuth: sun azimuth in radians (direction along the horizon, measured from south to west), e.g. 0 is south and Math.PI * 3/4 is northwest

Moon position

Returns an object with the following properties:

• altitude: moon altitude above the horizon in radians
• azimuth: moon azimuth in radians
• distance: distance to moon in kilometers
• parallacticAngle: parallactic angle of the moon in radians

Moon illumination

Returns an object with the following properties:

• fraction: illuminated fraction of the moon; varies from 0.0 (new moon) to 1.0 (full moon)
• phase: moon phase; varies from 0.0 to 1.0, described below
• angle: midpoint angle in radians of the illuminated limb of the moon reckoned eastward from the north point of the disk; the moon is waxing if the angle is negative, and waning if positive

Moon phase value should be interpreted like this:

By subtracting the parallacticAngle from the angle one can get the zenith angle of the moons bright limb (anticlockwise). The zenith angle can be used do draw the moon shape from the observers perspective (e.g. moon lying on its back).

Moon rise and set times

Returns an object with the following properties:

• rise: moonrise time as Date
• set: moonset time as Date
• alwaysUp: true if the moon never rises/sets and is always above the horizon during the day
• alwaysDown: true if the moon is always below the horizon

By default, it will search for moon rise and set during local user's day (frou 0 to 24 hours). If inUTC is set to true, it will instead search the specified date from 0 to 24 UTC hours.