In Oslo the longest day lasts almost 19 hours and the shortest less than six. Further north the sun may not set at all for weeks, or not rise. The explanation is the tilt of the Earth's axis, and the effects are bigger than most people realize.
The tilt that makes the seasons
The Earth's axis is tilted about 23.4 degrees relative to its orbit around the sun. In June the northern half is tilted toward the sun, so the sun is high in the sky and the days are long. In December it is tilted away, and the sun is low and the days are short.
The seasons are not caused by the distance to the sun. The Earth is actually closest to the sun in early January, in the middle of the northern winter.
The Arctic Circle
The Arctic Circle lies at about 66.5 degrees north, which is 90 minus the tilt of 23.4 degrees. North of this line, the sun stays above the horizon for at least one whole day around the summer solstice and below it for at least one day around the winter solstice. The farther north you go, the longer these periods become.
At the North Pole there is one sunrise and one sunset a year, giving about six months of daylight and six of night.
Midnight sun and polar night in Norway
In Tromsø, at 69.7 degrees north, the sun does not set from about May 20 to July 22, and it does not rise from about November 27 to January 15. In Hammerfest and Alta the periods are similar, and at the North Cape the midnight sun lasts from mid-May to late July.
On Svalbard, Longyearbyen has midnight sun from about April 19 to August 23 and polar night from about October 26 to February 15. For about four months of the year there is no real darkness.
Oslo: bright nights and short days
Oslo, at about 60 degrees north, does not have midnight sun, but the sun is up for almost 19 hours around the summer solstice, rising at around four in the morning and setting after 22:40. At midsummer the sky never becomes completely dark. In December the sun rises just after 09:15 and sets at about 15:10, giving less than six hours of daylight.
That is why Norwegians talk so much about light. The difference between the longest and shortest day in Oslo is around 13 hours.
Twilight explained
Daylight does not end the moment the sun sets. Civil twilight lasts until the sun is 6 degrees below the horizon, and there is enough light for outdoor activities. Nautical twilight lasts until 12 degrees and astronomical twilight until 18 degrees, when the sky is fully dark.
In southern Norway around midsummer the sun never gets 18 degrees below the horizon, so astronomical darkness does not occur, and you cannot see the faintest stars. In the north, even nautical twilight may last all night.
Polar night is not completely dark
During polar night in Tromsø there is a bluish twilight for a few hours around midday, which is known as the blue time. The sun is just below the horizon, and the light is enough to see without a lamp. In the middle of the polar night, the northern lights are at their most visible, because the sky is dark enough.
Even in the darkest weeks, the day is clearly different from the night, and daylight returns gradually, with a few minutes more each day.
Effects on sleep and daily life
People in the north adapt in many ways. In summer they use blackout curtains and sleep less, and in winter they use daylight lamps and spend time outdoors on bright days. Many people find the spring and autumn changes the biggest, because the daylight changes at its fastest rate, up to seven or eight minutes a day in some places.
If you have trouble sleeping in the bright summer, a dark room and a steady routine can help, and in winter many people find that morning light and time outdoors make the dark months easier.
Daylight on any date
The city pages on this site include articles with the sunrise and sunset times for the longest and shortest days. You can compare the daylight in cities from Oslo to Sydney, where the seasons are reversed, and with a world clock see what time it is there right now.