Table of Contents
What Determines Sunset Time?
Sunset time is governed by the same astronomical factors as sunrise: latitude, solar declination (day of year), and longitude within your time zone. The sun sets when the upper edge of the solar disk drops below the western horizon. Due to atmospheric refraction, the sun is actually about 0.83 degrees below the geometric horizon when it appears to be setting.
An interesting asymmetry exists: the latest sunset does not occur on the summer solstice but rather about a week later. Similarly, the earliest sunset occurs about two weeks before the winter solstice. This offset is caused by the equation of time and Earth's elliptical orbit.
Sunset Equation
where ω0 is the hour angle at sunset, φ is latitude, and δ is solar declination.
Latest & Earliest Sunsets (40.7°N)
| Period | Approximate Date | Sunset Time |
|---|---|---|
| Latest sunset | ~June 27 | ~8:31 PM |
| Earliest sunset | ~December 8 | ~4:28 PM |
| Equinox (March) | March 20 | ~7:08 PM |
| Equinox (Sept) | September 22 | ~7:02 PM |
Golden Hour & Photography
- Golden hour: Approximately the last hour before sunset when sunlight is warm and diffused. Ideal for portrait and landscape photography.
- Blue hour: About 20-30 minutes after sunset when the sky takes on deep blue tones. Perfect for cityscapes with artificial lights.
- Shadow length: Shadows grow extremely long near sunset, creating dramatic effects in photography and useful for sundial calculations.
Frequently Asked Questions
Why does the latest sunset not occur on the summer solstice?
The equation of time causes solar noon to shift relative to clock noon throughout the year. Near the June solstice, solar noon is getting later each day, which pushes the latest sunset to about June 27-28 at mid-latitudes, even though the longest day is June 20-21.
How does elevation affect sunset time?
Higher elevations see the sun set later because the horizon drops away. The correction is approximately: extra minutes = 2 * sqrt(elevation in meters) / 60. At 1000m elevation, sunset is roughly 2 minutes later than at sea level.
Why are sunsets often more colorful than sunrises?
During the day, human activity stirs up dust and aerosols in the lower atmosphere. These particles scatter blue and green light more than red, resulting in more vivid reds and oranges at sunset compared to the typically cleaner air at sunrise.