Is twilight shorter at the equator?

Photo via Flickr user ozyman.

Yes, twilight is shorter at the equator and longer closer to the poles.

The reason is the angle of the ecliptic – or path of the sun, moon and planets across our sky. As seen from the equator, at all times of the year, the sun’s path in relation to the horizon is more nearly vertical than it is as seen from farther north or south on Earth’s globe.

As seen from equatorial latitudes, the sun drops quickly down toward the horizon – and it just as quickly sinks below the horizon. So darkness falls suddenly. Meanwhile, as seen from northerly latitudes – say, Alaska – the sun’s path is more nearly parallel to the horizon. Traveling on that path, the sun stays closer to the horizon longer, even after it sets.

November 28, 2009

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