

Sunrise and sunset times in major world cities on the summer solstice. While locations in the Northern Hemisphere have their longest daylight period, cities in the Southern Hemisphere such as Sydney, Australia have their shortest. (Data source: timeanddate.com)

At 7:09 p.m. (EDT) today, the sun will shine directly overhead at the Tropic of Cancer while the North Pole reaches its maximum tilt towards the sun. For the Northern Hemisphere, this marks the official start of summer and the longest day of the year.



On the summer solstice, Earth’s northern hemisphere reaches its maximum tilt towards the sun. Locations north of the Arctic Circle experience 24 hours of daylight. See larger image. (NOAA)

Relationship between latitude, sun angle, and day length

Since day length depends on latitude, northern cities like New York and Chicago see the sun above the horizon for more than 15 hours. At lower latitudes the amount of daylight is shorter but the sun climbs higher in the sky. So while cities like Atlanta, Miami, and Los Angeles have somewhat shorter days during summer, the midday sun there is also more intense.

Related: The summer solstice - and other interesting sun facts - explained



Sunrise and sunset times on the summer solstice. Day length refers to the elapsed time from sunrise to sunset, not including twilight. (Data source: timeanddate.com)

As one moves north from the tropics towards the North Pole, the sun stays above the horizon longer but is also noticeably lower in the sky. At nearly 65ºN latitude, residents of Fairbanks, Alaska see the sun circle the sky for nearly 23 hours in mid-June. Yet even on the longest day of the year the sun shines at a very low 48.6º declination during midday. At this time of year areas along and north of the Arctic Circle experience 24-hour daylight.

The summer solstice in other cities around the world

Much of the continental U.S. enjoys 14 to 16 hours of daylight on the summer solstice, but how do other major world cities compare? Many cities in East Asia, such as Tokyo and Beijing, are at about the same latitude and have similar periods of sunlight. Other places – notably in Europe – get considerably more daylight than even the northernmost metropolitan areas of the mainland United States.

Across the Atlantic in London, for example, the sun stays above the horizon for well over 16 hours – from before 5 a.m. until after 9 p.m. Factor in the amount of light from dawn until dusk and the period of visible light extends beyond 18 hours. The graph below compares the day length and twilight duration of a handful of cities in the Northern Hemisphere. Note that locations in higher latitudes have not only longer days but also much longer periods of twilight (see graphical comparison).



The amount of visible light on the longest day of the year in the Northern Hemisphere. Day length refers to the period from sunrise to sunset. Civil twilight refers to the time before sunrise and after sunset when the sun is 6º or less below the horizon. (Data source: timeanddate.com)

Additional reading

Why the earliest sunrise is before the June solstice (EarthSky.org)

Day and night world map (timeanddate.com)

More from Capital Weather Gang

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Winter Solstice 2011

Autumn Equinox 2011

Summer Solstice 2011