Calculate Sunset Position

Sunset position refers to the exact location of the sun in the sky at the moment it disappears below the horizon. This calculation is important for astronomy, photography, and solar energy applications. Our calculator provides precise azimuth and altitude measurements for any location and date.

What is Sunset Position?

The sunset position is defined by two key measurements: azimuth and altitude. Azimuth is the angle between true north and the direction of the sunset, measured clockwise. Altitude is the angle between the horizon and the sun's position in the sky.

Understanding sunset position helps photographers position themselves for golden hour shots, astronomers track celestial events, and solar energy engineers optimize panel placement. The position changes throughout the year due to Earth's axial tilt and orbital motion.

How to Calculate Sunset Position

Calculating sunset position requires several inputs: geographic coordinates, date, and time zone. The most accurate method uses the solar position algorithm developed by the National Renewable Energy Laboratory (NREL).

Determine your latitude and longitude
Select the date and time
Account for your local time zone
Calculate solar declination
Compute hour angle at sunset
Determine azimuth and altitude

For precise calculations, the calculator uses the NREL SPA algorithm which accounts for atmospheric refraction and solar geometry.

Formula

The solar position algorithm calculates sunset position using these key equations:

Solar Declination (δ):

δ = -23.45° × cos(360/365 × (n + 10))

where n is the day of year (1-365)

Hour Angle at Sunset (ωs):

ωs = arccos(-tan(φ) × tan(δ))

where φ is latitude

Azimuth (A):

A = arctan(sin(ωs) / (-cos(ωs) × sin(φ) + cos(φ) × cos(δ)))

Altitude (h):

h = arcsin(sin(φ) × sin(δ) + cos(φ) × cos(δ) × cos(ωs))

Example Calculation

Let's calculate sunset position for New York City (40.7128° N, 74.0060° W) on June 21, 2023:

Day of year (n) = 172
Solar declination (δ) = -23.45° × cos(360/365 × 182) ≈ 23.44°
Hour angle at sunset (ωs) = arccos(-tan(40.7128°) × tan(23.44°)) ≈ 100.5°
Azimuth (A) = arctan(sin(100.5°) / (-cos(100.5°) × sin(40.7128°) + cos(40.7128°) × cos(23.44°))) ≈ 295.3°
Altitude (h) = arcsin(sin(40.7128°) × sin(23.44°) + cos(40.7128°) × cos(23.44°) × cos(100.5°)) ≈ -0.57°

The result shows the sun is setting at approximately 295.3° azimuth (northwest) with a negative altitude indicating it's below the horizon.

Frequently Asked Questions

What is the difference between azimuth and altitude?: Azimuth measures the compass direction of the sunset, while altitude measures how high the sun appears in the sky. Together they define the sun's exact position.
How does sunset position change throughout the year?: Sunset position changes significantly due to Earth's axial tilt. In summer, sunsets occur in the northwest, while in winter they occur in the southwest.
Can I use this calculator for photography?: Yes, sunset position data helps photographers determine the best locations and times for golden hour shots.
What factors affect sunset position accuracy?: Atmospheric refraction, local topography, and time zone adjustments can slightly affect the calculated position.
How often should I recalculate sunset position?: For most purposes, monthly recalculations are sufficient, though daily changes are noticeable near solstices.