Sun and sky
Civil, nautical and astronomical twilight, and the golden hour, explained
Every sunrise and sunset page on this site lists first light, last light, golden hour and three kinds of twilight. Here is what each threshold means and why the same twilight lasts 25 minutes in Singapore and all night in St Petersburg.
Last reviewed October 5, 2026About 3 min to readSite version v2026.10.1
Where sunset actually is
Sunset is the moment the top edge of the sun's disc disappears below the horizon. By convention that is computed as the moment the centre of the sun is 0.833 degrees below a flat horizon: 0.267 degrees for the sun's radius, and about 0.567 degrees for atmospheric refraction, which bends light over the horizon so that you see the sun for a few minutes after geometry says it has gone. Sunrise is the same calculation run backward.
Real horizons are not flat. A hill to the west brings sunset earlier; a view from a tall building delays it. Published times, including those on this site, assume sea level and a clear horizon, and are typically within a minute of almanac values at ordinary latitudes. The methodology page states the equations used.
The three twilight bands
| Band | Sun's altitude | What it is like |
|---|---|---|
| Civil twilight | 0 to 6 degrees below | Bright enough for outdoor work without lights. Street lamps come on near its end. The brightest planets appear. |
| Nautical twilight | 6 to 12 degrees below | The horizon is still visible against the sky, which is what sailors needed to take star sights. Most stars are out. |
| Astronomical twilight | 12 to 18 degrees below | The sky looks dark to the eye, but faint objects are still washed out for astronomers. Fully dark once the sun passes 18 degrees. |
The thresholds are definitions, not observations: they were chosen so that each band corresponds to a useful level of light. "First light" on the sunrise and sunset pages is the start of civil twilight in the morning, and "last light" is its end in the evening; the nautical and astronomical bands are listed below them.
Golden hour and blue hour
Photographers use two further bands that have no official definition. The golden hour is the period when the sun is low and the light is warm and soft, usually taken as the sun being between about 6 degrees above the horizon and the horizon itself; this site uses that 6-degree threshold. The blue hour is roughly the civil twilight band, when the sky is deep blue and artificial lights balance it.
Neither lasts an hour in general. Near the equator the sun drops almost vertically, so the golden hour can be twenty minutes; at 60 degrees north in summer, where the sun slides along the horizon, it can stretch across several hours.
Why twilight is short at the equator and endless in the north
The sun's path across the sky meets the horizon at a steep angle near the equator and a shallow angle near the poles. The steeper the angle, the faster the sun crosses the 6-degree band of civil twilight. At the equator civil twilight lasts about 22 to 24 minutes all year. At London's latitude it lasts about 35 minutes in winter and 45 in summer. At Reykjavik it can last more than an hour.
Go far enough north in summer and the sun never gets 18 degrees below the horizon at all, so astronomical twilight lasts all night: that is the case everywhere north of about 48.5 degrees around the June solstice, which includes Paris and Vancouver. North of about 60.5 degrees, civil twilight lasts all night, which is the "white night" of St Petersburg and Helsinki. North of the Arctic Circle, at 66.5 degrees, the sun does not set at all for part of the summer.
The sun pages handle each of these cases explicitly. Where a threshold is never crossed on a given date, the page says so in words, such as "no astronomical night", rather than printing a meaningless time.
See it on the site
- Sunrise and sunset by cityToday's sunrise, sunset, twilight bands and golden hour for over a thousand cities.
- Sun in LondonA mid-latitude example where every band has a start and an end all year.
- Sun in ReykjavikA high-latitude example with no astronomical night for much of the summer.