Sunrise / Sunset: How It Works
Sunrise and sunset times depend on your latitude, longitude and the date, and they shift in ways that surprise people — including the fact that the earliest sunset does not fall on the shortest day.
What determines the times
- Latitude — the dominant factor. Near the equator day length barely varies; near the poles it varies from continuous daylight to continuous night.
- Longitude — shifts the times within a timezone. The eastern edge of a wide timezone sees the sun rise noticeably earlier than the western edge.
- Date — the Earth's 23.4° axial tilt drives the annual cycle.
- Altitude — a higher vantage point sees the sun slightly earlier and later.
The definition of sunrise
Sunrise is the moment the upper edge of the sun appears above the horizon, not its centre. Atmospheric refraction bends light around the curve of the Earth, so the sun is actually below the geometric horizon at the moment it appears — by roughly the width of its own disc.
This means daylight lasts a few minutes longer than pure geometry predicts, and it is why the equinox has slightly more than twelve hours of daylight rather than exactly twelve.
Twilight
| Phase | Sun below horizon | Conditions |
|---|---|---|
| Civil twilight | 0–6° | Outdoor activity still possible without lights |
| Nautical twilight | 6–12° | Horizon still visible at sea |
| Astronomical twilight | 12–18° | Faint objects begin to be visible |
| Night | Below 18° | Full darkness |
The golden hour — favoured by photographers for its warm, soft light — is roughly the hour after sunrise and before sunset. The blue hour is the period of civil twilight either side, when the sky holds a deep even blue.
Why the earliest sunset is not the shortest day
In the northern hemisphere the earliest sunset falls in early December and the latest sunrise in early January, with the solstice — the shortest day — between them. The reverse holds in June.
The cause is that solar noon drifts through the year, because the Earth's orbit is elliptical and its axis is tilted. The combined effect is described by the equation of time, and it means the sun is up to about 16 minutes ahead of or behind clock time depending on the date. Day length and clock times therefore peak on different dates.
The polar extremes
Above the Arctic Circle and below the Antarctic Circle, the sun remains above the horizon continuously around the summer solstice and below it around the winter one. The further from the circle, the longer these periods last — at the poles themselves the year is a single day and a single night.
Practical uses
Photographers plan around golden and blue hour; gardeners track daylight hours for growing conditions; solar installers use the sun's path to position panels; and several religious observances are defined by sunrise, sunset or twilight. For religious timings, note that different traditions use different definitions of the relevant moment — follow your community's published times rather than a general calculator.