Bonus List

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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Copyright 2004 Brandt Maxwell.