Twilight

gkell1

Living close to the Equator in a place like Bali,an observer moving there from more Northern latitudes like ours will notice two things,there is no real see-saw between summer and winter when it comes to the amount of daylight or darkness and it rapidly moves from daylight to darkness whereas twilight is a more drawn out an gentle affair at our latitudes.

With a minor nod to atmospheric diffraction,a person living on the equator exits the circle of illumination roughly 12 hours after entering it as the Earth turns in its daily cycle,this will happen 365 in a non-leap year and 366 times in a leap year.

The reason why there is a dramatic shift from daylight to darkness at the equator and places close to it as any tourist will testify,is that the maximum equatorial speed is 1037.5 miles per hour whereas at latitude 60 degrees,roughly in line with Bergen,Norway,the speed through the circle of illumination is 525 miles per hour.In short,the slower the rotational speed the longer the twilight as the distance traveled by each latitude varies with time -

http://www.ncgia.ucsb.edu/education/curricula/giscc/units/u014/tables/table02.html

Scientists,of course,dispute the values for each 4 degrees of daily rotation notwithstanding how simple the correspondence is between rotational speed and twilight length.

hal9000

nice info. For a minute there i thought it was going to be about those horrible books and movies! :pac:

Beeker

gkell1 wrote: »

Living close to the Equator in a place like Bali,an observer moving there from more Northern latitudes like ours will notice two things,there is no real see-saw between summer and winter when it comes to the amount of daylight or darkness and it rapidly moves from daylight to darkness whereas twilight is a more drawn out an gentle affair at our latitudes.

With a minor nod to atmospheric diffraction,a person living on the equator exits the circle of illumination roughly 12 hours after entering it as the Earth turns in its daily cycle,this will happen 365 in a non-leap year and 366 times in a leap year.

The reason why there is a dramatic shift from daylight to darkness at the equator and places close to it as any tourist will testify,is that the maximum equatorial speed is 1037.5 miles per hour whereas at latitude 60 degrees,roughly in line with Bergen,Norway,the speed through the circle of illumination is 525 miles per hour.In short,the slower the rotational speed the longer the twilight as the distance traveled by each latitude varies with time -

http://www.ncgia.ucsb.edu/education/curricula/giscc/units/u014/tables/table02.html

Scientists,of course,dispute the values for each 4 degrees of daily rotation notwithstanding how simple the correspondence is between rotational speed and twilight length.

Nice articles you have been posting over the past few days. Make for interesting reading. Thanks.

gkell1

Beeker wrote: »

Nice articles you have been posting over the past few days. Make for interesting reading. Thanks.

Thanks for the comment.It gets interesting if you look even closer as there are two types of global twilights to consider.In 3 months time the Antarctic stations at the South pole will turn through the circle of illumination and into 6 months of daylight while ,at the same time,the North pole will descend into 6 months of darkness.As 6 months of darkness followed by 6 months of daylight with a brief orbital twilight at the equinoxes requires a dynamic to explain that cycle,it is easier to set daily rotation aside altogether as it plays no part and look at what the Earth's orbital motion is doing.It takes a little interpretative effort and an imitation analogy but I know myself it can give a person a headache at first even if it is worth it to come through in the end with a more satisfying picture.