Sunset Calculator
Calculate precise sunset times and twilight periods using astronomical formulas with atmospheric refraction
Calculate Sunset Time
Location
Positive for North, negative for South (-90 to 90)
Positive for East, negative for West (-180 to 180)
Day of year: 288
Different definitions of sunset based on sun angle
Sunset Calculation Results
Calculation Details
288
-8.67°
-83.58°
90.833°
200.58°
281.51°
Location Analysis
Example Calculations
Los Angeles (Summer Solstice)
Location: 34.0522°N, 118.2437°W
Date: June 21st (Day 172)
Solar Declination: ~23.4° (maximum)
Sunset Time: ~8:08 PM (latest of the year)
Day Length: ~14.5 hours
London, UK (Winter Solstice)
Location: 51.5074°N, 0.1278°W
Date: December 21st (Day 355)
Solar Declination: ~-23.4° (minimum)
Sunset Time: ~3:53 PM (earliest of the year)
Day Length: ~7.5 hours
Types of Dusk
Apparent Sunset
Sun's edge crosses horizon (90.833°)
Standard sunset time with refraction
Civil Twilight
Sun 6° below horizon (96°)
Street lights turn on
Nautical Twilight
Sun 12° below horizon (102°)
Horizon barely visible at sea
Astronomical Twilight
Sun 18° below horizon (108°)
Complete astronomical darkness
Quick Locations
Key Formulas
Hour Angle
ha = -arccos((cos(z) - sin(δ)·sin(φ))/(cos(δ)·cos(φ)))
Solar Declination
δ = arcsin(0.39782 · sin(L))
True Longitude
L = M + 1.916·sin(M) + 0.020·sin(2M) + 282.634
Mean Anomaly
M = 0.9856 · t - 3.289
Understanding Sunset Calculations
What is Sunset?
Sunset is the moment when the upper edge of the Sun disappears below the western horizon. Like sunrise, this definition accounts for atmospheric refraction, which bends sunlight and makes the Sun appear slightly higher than its geometric position.
Types of Dusk
- •Civil dusk: Sun 6° below horizon - street lights turn on
- •Nautical dusk: Sun 12° below horizon - horizon barely visible
- •Astronomical dusk: Sun 18° below horizon - complete darkness
Atmospheric Refraction
Earth's atmosphere bends sunlight by approximately 0.58°, making the Sun appear higher than its true position. This effect extends both sunrise and sunset times, giving us about 6 extra minutes of daylight each day.
Key Differences from Sunrise
The Calculation Process
1. Solar Position
Calculate the Sun's position using astronomical formulas including mean anomaly, true longitude, and declination.
2. Hour Angle
Determine when the Sun reaches the specified angle below the horizon using spherical trigonometry.
3. Local Time
Convert from UTC to local time accounting for longitude, time zone, and daylight saving adjustments.
Sunset Colors and Phenomena
Why Sunsets Are Colorful
- • Rayleigh scattering affects short wavelengths more
- • Longer path through atmosphere filters blue light
- • Red and orange wavelengths penetrate better
- • Dust and particles enhance color intensity
- • Green flash phenomenon at very clear horizons
Photography Tips
- • Golden hour starts ~1 hour before sunset
- • Blue hour occurs during civil twilight
- • Use graduated filters for dynamic range
- • Plan timing with calculator results
- • Consider cloud formations for dramatic effects