Module: SunCalc

Defined in:
lib/suncalc.rb,
lib/suncalc/version.rb

Constant Summary collapse

RAD =

Shortcuts for easier to read equations

Math::PI / 180
DAY_MS = 
1000 * 60 * 60 * 24
J1970 = 
2440588
J2000 = 
2451545
E = 
RAD * 23.4397
J0 = 
0.0009
SDIST = 
149598000
HC = 
0.133 * RAD
TIMES = 
[
    [-0.833, :sunrise, :sunset],
    [-0.3, :sunrise_end, :sunset_start],
    [-6, :dawn, :dusk],
    [-12, :nautical_dawn, :nautical_dusk],
    [-18, :night_end, :night],
    [6, :golden_hour_end, :golden_hour]
]
VERSION = 
"1.2.0"

Class Method Summary collapse

Class Method Details

.add_time(angle, rise_name, set_name) ⇒ Object

Sun times configuration (angle, morning name, evening name)



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# File 'lib/suncalc.rb', line 105

def self.add_time(angle, rise_name, set_name)
    TIMES << [angle, rise_name, set_name]
end

.altitude(h, phi, dec) ⇒ Object 



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# File 'lib/suncalc.rb', line 52

def self.altitude(h, phi, dec)
    Math::asin(Math::sin(phi) * Math::sin(dec) + Math::cos(phi) * Math::cos(dec) * Math::cos(h))
end

.approx_transit(ht, lw, n) ⇒ Object 



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# File 'lib/suncalc.rb', line 114

def self.approx_transit(ht, lw, n)
    J0 + (ht + lw) / (2 * Math::PI) + n
end

.astro_refraction(h) ⇒ Object

Atmospheric refraction correction (Meeus formula 16.4). Input/output in radians. Clamps h to >= 0 to avoid the div/0 singularity at h ≈ -0.0890.



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# File 'lib/suncalc.rb', line 62

def self.astro_refraction(h)
    h = 0 if h < 0
    0.0002967 / Math.tan(h + 0.00312536 / (h + 0.08901179))
end

.azimuth(h, phi, dec) ⇒ Object 



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# File 'lib/suncalc.rb', line 48

def self.azimuth(h, phi, dec)
    Math::atan2(Math::sin(h), Math::cos(h) * Math::sin(phi) - Math::tan(dec) * Math::cos(phi))
end

.declination(l, b) ⇒ Object 



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# File 'lib/suncalc.rb', line 44

def self.declination(l, b)
    Math::asin(Math::sin(b) * Math::cos(E) + Math::cos(b) * Math::sin(E) * Math::sin(l))
end

.ecliptic_longitude(m) ⇒ Object 



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# File 'lib/suncalc.rb', line 72

def self.ecliptic_longitude(m)
    c = RAD * (1.9148 * Math::sin(m) + 0.02 * Math::sin(2 * m) + 0.0003 * Math::sin(3 * m))
    p = RAD * 102.9372

    m + c + p + Math::PI
end

.from_julian(j) ⇒ Object 



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# File 'lib/suncalc.rb', line 29

def self.from_julian(j)
    Time.at(((j + 0.5 - J1970) * DAY_MS)/1000).utc
end

.get_moon_illumination(date = Time.now) ⇒ Object

Calculations for illumination parameters of the moon



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# File 'lib/suncalc.rb', line 231

def self.get_moon_illumination(date = Time.now)
    d = to_days(date)
    s = sun_coords(d)
    m = moon_coords(d)

    phi = Math::acos(Math::sin(s[:dec]) * Math::sin(m[:dec]) + Math::cos(s[:dec]) * Math::cos(m[:dec]) * Math::cos(s[:ra] - m[:ra]))
    inc = Math::atan2(SDIST * Math::sin(phi), m[:dist] - SDIST * Math::cos(phi))
    angle = Math::atan2(Math::cos(s[:dec]) * Math::sin(s[:ra] - m[:ra]), Math::sin(s[:dec]) * Math::cos(m[:dec]) - Math::cos(s[:dec]) * Math::sin(m[:dec]) * Math::cos(s[:ra] - m[:ra]))

    result = {
        :fraction => (1 + Math::cos(inc)) / 2,
        :phase => 0.5 + 0.5 * inc * (angle < 0 ? -1 : 1) / Math::PI,
        :angle => angle
    }

    result
end

.get_moon_position(date, lat, lng) ⇒ Object 



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# File 'lib/suncalc.rb', line 211

def self.get_moon_position(date, lat, lng)
    lw = RAD * -lng
    phi = RAD * lat
    d = to_days(date)

    c = moon_coords(d)
    th = sidereal_time(d, lw) - c[:ra]
    h = altitude(th, phi, c[:dec])
    # Meeus formula 14.1
    pa = Math.atan2(Math.sin(th), Math.tan(phi) * Math.cos(c[:dec]) - Math.sin(c[:dec]) * Math.cos(th))

    {
        :azimuth => azimuth(th, phi, c[:dec]),
        :altitude => h + astro_refraction(h),
        :distance => c[:dist],
        :parallactic_angle => pa
    }
end

.get_moon_times(date, lat, lng, in_utc = true) ⇒ Object 



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# File 'lib/suncalc.rb', line 253

def self.get_moon_times(date, lat, lng, in_utc = true)
    t = if in_utc
        Time.utc(date.year, date.month, date.day)
    else
        Time.local(date.year, date.month, date.day)
    end
    h0 = get_moon_position(t, lat, lng)[:altitude] - HC

    rise = false
    set = false
    ye = 0

    (1..24).step(2) do |i|
        h1 = get_moon_position(hours_later(t, i), lat, lng)[:altitude] - HC
        h2 = get_moon_position(hours_later(t, i + 1), lat, lng)[:altitude] - HC 

        a = (h0 + h2) / 2 - h1
        b = (h2 - h0) / 2
        xe = -b / (2 * a)
        ye = (a * xe + b) * xe + h1
        d = b * b - 4 * a * h1
        
        roots = 0

        if d >= 0
            dx = Math::sqrt(d) / (a.abs * 2)

            x1 = xe - dx
            x2 = xe + dx

            if x1.abs <= 1 
                roots += 1
            end
            
            if x2.abs <= 1
                roots += 1
            end

            if x1 < -1
                x1 = x2
            end
        end

        if roots === 1
            if h0 < 0
                rise = i + x1
            else
                set = i + x1
            end
        elsif roots === 2
            rise = i + (ye < 0 ? x2 : x1)
            set = i + (ye < 0 ? x1 : x2)
        end
        
        break if rise and set

        h0 = h2
    end

    result = {}
    if rise
        result[:rise] = hours_later(t, rise)
    end
    
    if set
        result[:set] = hours_later(t, set)
    end

    if not rise and not set
        result[ye > 0 ? :alwaysUp : :alwaysDown] = true
    end

    result
end

.get_position(date, lat, lng) ⇒ Object

Calculate sun position for a given date and latitude/longitude



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# File 'lib/suncalc.rb', line 91

def self.get_position(date, lat, lng)
    lw = RAD * -lng
    phi = RAD * lat
    d = to_days(date)
    c = sun_coords(d)
    h = sidereal_time(d, lw) - c[:ra]

    { :azimuth => azimuth(h, phi, c[:dec]),
      :altitude => altitude(h, phi, c[:dec])
    }
end

.get_set_j(h, lw, phi, dec, n, m, l) ⇒ Object

Returns set time for the given sun altitude



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# File 'lib/suncalc.rb', line 133

def self.get_set_j(h, lw, phi, dec, n, m, l)
    w = hour_angle(h, phi, dec)
    a = approx_transit(w, lw, n)
    solar_transit_j(a, m, l)
end

.get_times(date, lat, lng, height = 0) ⇒ Object

Calculate sun times for a given date and latitude/longitude. Optional height (meters above the horizon) corrects for observer elevation.



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# File 'lib/suncalc.rb', line 141

def self.get_times(date, lat, lng, height = 0)
    lw = RAD * -lng
    phi = RAD * lat
    dh = observer_angle(height)

    d = to_days(date)
    n = julian_cycle(d, lw)
    ds = approx_transit(0, lw, n)

    m = solar_mean_anomaly(ds)
    l = ecliptic_longitude(m)
    dec = declination(l, 0)

    jnoon = solar_transit_j(ds, m, l)

    result = {
        :solar_noon => from_julian(jnoon),
        :nadir => from_julian(jnoon - 0.5)
    }

    TIMES.each do |time|
        h0 = (time[0] + dh) * RAD
        begin
            jset = get_set_j(h0, lw, phi, dec, n, m, l)
            jrise = jnoon - (jset - jnoon)
            result[time[1]] = from_julian(jrise)
            result[time[2]] = from_julian(jset)
        rescue Math::DomainError
            # The sun never crosses this altitude on this date — polar
            # day or polar night for this particular event.
            result[time[1]] = nil
            result[time[2]] = nil
        end
    end

    # If sunrise/sunset don't occur, decide whether the sun was above the
    # horizon all day (always_up) or below it all day (always_down) by
    # looking at the altitude at solar noon (where hour angle = 0).
    if result[:sunrise].nil? && result[:sunset].nil?
        noon_altitude = altitude(0, phi, dec)
        if noon_altitude > 0
            result[:always_up] = true
        else
            result[:always_down] = true
        end
    end

    result
end

.hour_angle(h, phi, d) ⇒ Object 



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# File 'lib/suncalc.rb', line 122

def self.hour_angle(h, phi, d)
    Math::acos((Math::sin(h) - Math::sin(phi) * Math::sin(d)) / (Math::cos(phi) * Math::cos(d)))
end

.hours_later(date, h) ⇒ Object 



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# File 'lib/suncalc.rb', line 249

def self.hours_later(date, h)
    Time.at(date.to_f + (h * (DAY_MS/1000)) / 24).utc 
end

.julian_cycle(d, lw) ⇒ Object

Calculations for sun times



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# File 'lib/suncalc.rb', line 110

def self.julian_cycle(d, lw)
    (d - J0 - lw / (2 * Math::PI)).round
end

.moon_coords(d) ⇒ Object

Moon calculations



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# File 'lib/suncalc.rb', line 192

def self.moon_coords(d)
    el = RAD * (218.316 + 13.176396 * d)
    m = RAD * (134.963 + 13.064993 * d)
    f = RAD * (93.272 + 13.229350 * d)

    l = el + RAD * 6.289 * Math::sin(m)
    b = RAD * 5.128 * Math::sin(f)
    dt = 385001 - 20905 * Math::cos(m)
    

    result = {
        :ra => right_ascension(l, b),
        :dec => declination(l, b),
        :dist => dt
    }

    result
end

.observer_angle(height) ⇒ Object

Apparent angle of the horizon below the observer, in degrees, from a given observer height in meters. Used to correct sun rise/set times for elevation.



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# File 'lib/suncalc.rb', line 128

def self.observer_angle(height)
    -2.076 * Math.sqrt(height) / 60
end

.right_ascension(l, b) ⇒ Object

General calculations for position



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# File 'lib/suncalc.rb', line 40

def self.right_ascension(l, b)
    Math::atan2(Math::sin(l) * Math::cos(E) - Math::tan(b) * Math::sin(E), Math::cos(l))
end

.sidereal_time(d, lw) ⇒ Object 



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# File 'lib/suncalc.rb', line 56

def self.sidereal_time(d, lw)
    RAD * (280.16 + 360.9856235 * d) - lw
end

.solar_mean_anomaly(d) ⇒ Object

General sun calculations



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# File 'lib/suncalc.rb', line 68

def self.solar_mean_anomaly(d)
    RAD * (357.5291 + 0.98560028 * d)
end

.solar_transit_j(ds, m, l) ⇒ Object 



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# File 'lib/suncalc.rb', line 118

def self.solar_transit_j(ds, m, l)
    J2000 + ds + 0.0053 * Math::sin(m) - 0.0069 * Math::sin(2 * l)
end

.sun_coords(d) ⇒ Object 



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# File 'lib/suncalc.rb', line 79

def self.sun_coords(d)
    @result = []
    sM = solar_mean_anomaly(d)
    eL = ecliptic_longitude(sM)


    { :dec => declination(eL, 0),
      :ra => right_ascension(eL, 0)
    }
end

.to_days(date) ⇒ Object 



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# File 'lib/suncalc.rb', line 33

def self.to_days(date)
    to_julian(date) - J2000
end

.to_julian(date) ⇒ Object

Date/time constants and conversions



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# File 'lib/suncalc.rb', line 25

def self.to_julian(date)
    (date.to_f * 1000) / DAY_MS - 0.5 + J1970
end