How sunset times are calculated

What Exactly Is a Sunset Time?

A sunset time is the precise moment when the upper edge of the sun disappears below the horizon at a given location. This isn't a rough guess — it's a calculation rooted in astronomy. The sun appears to set because the Earth rotates, but the exact second depends on where you are on the planet, the time of year, and even the weather in the air above you. At sunset.now, we turn that celestial math into easy-to-read times for any city.

The Core Variables: Location and Date

The two biggest factors in calculating sunset are your geographic coordinates and the calendar date. Your latitude determines how steeply the sun tracks across the sky. A place near the equator sees the sun drop almost straight down, which means a shorter twilight. But head north to Chicago or Seattle, and the sun takes a long, angled path, making sunset last longer. Your longitude also matters because it sets your official time zone, shifting the sunset time relative to the clock. For a deeper dive, see how latitude affects sunset times.

Why the Sun Appears to Set Earlier (or Later) Than It Should

If you've ever checked a sunset time and thought, 'That feels early,' atmospheric refraction is the reason. Earth's atmosphere bends sunlight upward as it passes through, so we see the sun for a few extra minutes after it has truly gone below the horizon. This bending is strongest near the horizon, which is why the sun looks slightly flattened at sunset. It's also why the official sunset definition uses the upper limb of the sun — the very top edge — not the center.

Because refraction varies with air pressure and temperature, calculators always factor in standard atmospheric conditions. At sunset.now, we use the best available astronomical algorithms to account for that bending, giving you times you can trust. For more on what happens at those twilight moments, visit twilight explained.

How Seasons and Solstices Shift Sunset Times

The sun's declination — how far north or south it is — changes daily, and that directly shifts sunset. Around the summer solstice explained, the sun climbs high in the sky and sets late, especially in northern locations. By the winter solstice explained, the opposite happens: early sunsets and long nights. The earliest sunset of the year usually occurs a week or two before the solstice, thanks to the mismatch between clock time and solar time. This is also why latest sunset of the year happens days after the summer solstice.

If you live in a region that observes daylight saving time, that artificial clock shift can make sunset times seem to jump by an hour overnight. Learn more in our guide to daylight saving time and sunset.

The Role of Solar Noon and Equation of Time

Most people think noon is when the sun is highest. But 'solar noon' — the moment the sun crosses your local meridian — rarely aligns with 12:00 p.m. on your clock. The difference comes from the Earth's elliptical orbit and axial tilt. This is called the 'equation of time,' and it can push solar noon forward or backward by as much as 16 minutes. Since sunset is defined as the period after solar noon plus half the day length, any shift in solar noon directly adjusts sunset. Visit what is solar noon for the full explanation.

How Sunset.now Calculates Your Local Time

Every calculation on sunset.now starts with the city's exact latitude and longitude. We then apply the date, time zone, and daylight saving rules to produce a daily time for that spot. Our engine also checks for things like whether a city is on a time zone border, so you don't get a sunset time that's technically correct for the coordinates but wrong for your life. You can explore times for any location — whether you're planning a shoot or just want to catch the evening colors. See our apps and tools for sunset times to make planning even easier.

Want to share these times with your audience? You can add the times to your own site with our embeddable widget.

Beyond the Sunset: What Makes a Good Sunset

Calculated times only get you so far. The experience of a sunset depends on clouds, air quality, and your vantage point. Clear skies give a fast, bright fade, while a scattering of clouds can create brilliant reds and oranges — read more about why sunsets are red and how clouds affect sunsets. If you're a photographer chasing that perfect shot, you'll want to know about golden hour vs blue hour and how to use both.

To get the exact sunset time for your city tonight — or any night of the year — check sunset.now. We do the math so you can enjoy the view.

Frequently asked questions

Why do sunset times change so much from winter to summer?

Because the Earth is tilted on its axis, the sun's path across the sky shifts dramatically. In summer, the sun is higher and sets later; in winter, it sets much earlier. This effect is more extreme the farther you are from the equator.

Does the moon affect sunset times?

No. The moon has no effect on sunset times. Sunset is purely a function of the sun's position relative to Earth's horizon, determined by location and date.

Why is my sunset time different from a friend's in the same time zone?

Longitude differences within a time zone cause solar noon to shift. Two cities in the same time zone can have sunset times that differ by 30 minutes or more, especially if one is far east and the other far west.

Can I use sunset.now to find times for past or future dates?

Yes. Sunset.now provides accurate sunset times for any date you choose, so you can plan ahead or look back at a special day.

How sunset times are calculated — sunset.now guide