Sunrise & sunset calculator

How sunrise and sunset are calculated

Sunrise and sunset depend on where you are and on the date, not on the time zone. For each city we take its latitude and longitude and work out where the sun is in the sky through the day, using the same family of formulas as the NOAA Solar Calculator: the Earth’s position in its orbit gives the sun’s declination (how far north or south of the equator it is overhead) and the time of solar noon, and simple spherical trigonometry gives the moment the sun crosses a chosen height above or below the horizon.

Sunrise and sunset are defined as the moment the top edge of the sun touches a flat horizon. Because the sun is a disc about half a degree wide and the atmosphere bends its light over the horizon, that happens when the centre of the sun is 0.833° below the horizon. The result is converted to the city’s local clock time — including daylight saving time on that date — by your browser’s time zone database.

Twilight, golden hour and blue hour

Light doesn’t switch on and off at sunrise and sunset. The page splits the day into four kinds of sky, shown as colours on the bar above:

• Night — the sun is more than 6° below the horizon.
• Blue hour — the sun is between 6° and 4° below the horizon. The sky is a deep, even blue and artificial lights balance with the sky. It starts at civil dawn in the morning and ends at civil dusk in the evening, the points where there is enough natural light to work outdoors.
• Golden hour — the sun is between 4° below and 6° above the horizon. Light is warm and comes in low, so shadows are long and soft. Photographers have no single official definition; −4° to +6° is a common one, and it is the one we use everywhere on this site.
• Daylight — the sun is more than 6° up.

Close to the equator the sun rises and sets almost vertically, so twilight is short — about 40 minutes of golden hour and under 10 minutes of blue hour, morning and evening. Far from the equator the sun crosses the horizon at a shallow angle and they stretch out; in Helsinki or Reykjavik in early summer the golden light lasts for hours and the sky never gets fully dark.

Day length through the year

The table above shows how long the sun is up on the 21st of every month, which lands close to both solstices and both equinoxes. At the equinoxes in March and September, day and night are roughly equal everywhere. Towards the June solstice, days get longer north of the equator and shorter south of it; in December it is the other way around. The note under the table gives the actual longest and shortest day of the year for the city you picked.

“Day length” here is the time from sunrise to sunset. Because the definition uses the top edge of the sun and includes refraction, even on the equinox a day is a few minutes longer than 12 hours.

Midnight sun and polar night

Inside the Arctic and Antarctic Circles there are days when the sun never sets, and days when it never rises. The calculator says so instead of showing a time. None of our 150 cities is that far north, but Reykjavik and Anchorage come close. At midsummer the sun dips only about 2.5° below the horizon in Reykjavik, so there is no night and no blue hour at all — just one long golden twilight from sunset to sunrise. In Anchorage the sky never gets darker than blue hour. In midwinter the opposite happens: in Reykjavik the sun climbs less than 3° at noon, so the whole short day is one golden hour.