HOW MUCH DOES TWILIGHT VARY AROUND THE WORLD?
A common phrase of Northerners who visit the tropics is "It gets dark almost immediately after sunset." While this is not quite true (there's generally around 50 minutes of nautical twilight at the equator), there is considerably more twilight closer to the poles than the equator, since the "angular momentum" of the earth is less near the poles. Twilight lasts longer during summer than winter, with the difference becoming greater as one traverses away from the equator. On the first day of summer (and usually other nearby days), north of about 54 degrees North (or south of about 54 deg. S.), twilight will last all night, except north of the Arctic Circle (or south of the Antarctic Circle) where there is no twilight because the sun is up all night!

Nautical twilight most closely corresponds to the period of time after sunset (or before sunrise) when some solar light can still be seen in the sky. Technically, nautical twilight ends when the sun is 12 degrees (angle) below the horizon. Of course, other factors, such as cloudiness, haze or mountains will also determine how long light can be seen in the sky; usually the actual twilight will be a bit shorter. Other types of twilight include "civil twilight" (the period of time when objects can easily be seen outdoors and occurs until the sun is 6 degrees below the horizon) and "astronomical twilight" (when the sun contributes at least a very minor amount to the sky's illumination, whether visible by humans or not, and occurs until the sun is 18 degrees below the horizon).



Here are some summer and winter solstice (nautical) twilight lengths for cities around the world, in minutes:

CITY, COUNTRY/STATE Fairbanks, Alaska (USA) Reykjavik, Iceland Anchorage, Alaska (USA) Moscow, Russia Berlin, Germany London, United Kingdom Vancouver, B.C. (Canada) Paris, France Seattle, Washington Montreal, Quebec (Canada) Toronto, Ontario (Canada) Chicago, Illinois (USA) New York, New York (USA) Beijing, China Washington, D.C. (USA) Athens, Greece San Francisco, California (USA) Tokyo, Japan Los Angeles, Californa (USA) Sydney, Australia Dallas, Texas (USA) Cairo, Egypt Delhi, India Miami, Florida (USA) Hong Kong, China Honolulu, Hawaii (USA) Mexico City, Mexico Manila, Philippines Singapore, Singapore*

SUMMER SOLSTICE all night all night all night all night 136 124 107 105 99 91 85 81 78 76 74 73 71 69 67 67 66 62 62 59 57 56 55 53 50

WINTER SOLSTICE 163 154 126 99 88 86 80 80 77 74 71 69 68 66 65 64 63 62 61 61 60 58 57 55 53 53 53 52 50

* Nautical twilight near the equator is longest during the winter and summer solstices (50 min.) and shortest during the spring and fall equinoxes (47 min.).



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