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Forever Twilight

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April 27, 2009 – Comments (2)

This has nothing to do with investments, but with twilight, the time between day and night.

The change in the length of days up north can be extremely dramatic.  Around the first days of spring or fall the length of day is changing by about 45 minutes in week where I am.  In the winter we decline to about a 6 hour day for the first day of winter.  So, it seemed to me that we should have a 6 hour night on our shortest night in the summer.  Well, already we are up to about a 19 hour day and it is still almost 2 months from summer, yet the calculations say the days should be more like about 16 hours. (Yet even with 19 hour days we managed about a foot and a half of snow fall this past week...)

So, enter twilight.  I learned that everywhere on Earth the day is longer then the night because of twilight, about 7 minutes close to the equator.  But up here around the 60th parallel, well, it is in the range where civil twilight can occur all night.  There are 3 kinds of twilight, civil, nautical and astronomical twilight.  To most of us astronomical twilight looks the same as night, but it prevents seeing some stars in the sky, something most of us would not notice.  Civil twilight is the first part of twilight and from about a latitude of 60 degrees north civil twilight can continue all night, and from 54 degrees the night goes through civil and then nautical twilight.

For the month on either side of the summer solstice the length of day is changing very slowly, so around here the nights never leave twilight for a couple months of the year and we have no night.

2 Comments – Post Your Own

#1) On April 27, 2009 at 8:22 AM, catoismymotor (< 20) wrote:

60th parallel? Is that where Forks, Washington is?

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#2) On April 27, 2009 at 9:11 AM, dwot (46.92) wrote:

I am in northern Canada catoismymotor, just over the border into the northwest territories.

It was more interesting to me looking at sunrise today.  At 6:30 am it was still twilight, a beautiful pink/orange sky around where the sun was getting ready to peek through, but light out.  Now, at 7:10 the sun is above the horizon.  I was not watching it the whole time so I am not sure when the sun first peeked over the horizon, but it started getting light around 6 am.  

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