Sun set/rise time

[Holton181]

Hi

First, thank you Jose for a really great mapping app!



Now to my question:

What is the definition of sun set/rise time for the 'SOLAR' in 'Settings-Application-Sun set/rise time'?

I live at latitude 66.6°N, just north of the polar circle. That means the sun never set at summer solstice and never rises at winter solstice. But I have noticed that when I select 'SOLAR' oruxmaps still indicates the sun sets at summer solstice and rise at winter solstice. During last winter solstice oruxmaps indicated the sun to be up for about 2.5h (if I remember correctly). That is quite much, not really just a numerical error.



I know there are several definitions for the sun set/rise time due to the fact the sun is not an infinitely small dot, but rather a disk with an area. Different definitions can be when the upper edge (fully down), the center or the lower edge (fully up) of that disk is at the horizon. Also atmospheric refraction might/might not be accounted for. Unfortunately I have not found the exact definition for the polar circles, but I believe it is the disk center at the horizon, atmospheric refraction not accounted for. But I might be wrong.



A small request:

Is it possible to get a setting of the sun set/rise time that corresponds to the polar circles definition (the real one, not my guess)?



Best Regards

/Jens

[orux]

Hi

First, thank you Jose for a really great mapping app!



Now to my question:

What is the definition of sun set/rise time for the 'SOLAR' in 'Settings-Application-Sun set/rise time'?

I live at latitude 66.6°N, just north of the polar circle. That means the sun never set at summer solstice and never rises at winter solstice. But I have noticed that when I select 'SOLAR' oruxmaps still indicates the sun sets at summer solstice and rise at winter solstice. During last winter solstice oruxmaps indicated the sun to be up for about 2.5h (if I remember correctly). That is quite much, not really just a numerical error.



I know there are several definitions for the sun set/rise time due to the fact the sun is not an infinitely small dot, but rather a disk with an area. Different definitions can be when the upper edge (fully down), the center or the lower edge (fully up) of that disk is at the horizon. Also atmospheric refraction might/might not be accounted for. Unfortunately I have not found the exact definition for the polar circles, but I believe it is the disk center at the horizon, atmospheric refraction not accounted for. But I might be wrong.



A small request:

Is it possible to get a setting of the sun set/rise time that corresponds to the polar circles definition (the real one, not my guess)?



Best Regards

/Jens

Hi, Jens;



OruxMaps uses the same algorith than this web site:



http://aa.usno.navy.mil/data/docs/RS_OneYear.php">http://aa.usno.navy.mil/data/docs/RS_OneYear.php



The app checks if there is sunrise and sunset time before displaying the values.



Tell me if the values of this web site  matches with the values you expect.

[Holton181]

Thank you very much for the link.

They use the definition of the rise and set time as when the upper part of the sun touches the horizon. That gives the midnight sun will rise at Jun 4th and set at July 7th at my location this year (2014) and the sun will indeed always rise and set December 21 th (a day of 2h & 7min 2014).



After further reading my guess about the polar circles seems to be right. The center of the sun is the point of measure and refraction are not accounted for, i.e. the polar circles are pure geometrical features placed at the same angel from the poles as the tilt of the earth, 90°-23°27'=66°33'.

I found a good reference explaining some of this here:

http://nwtresearch.com/sites/default/files/the-polar-night.pdf">//http://nwtresearch.com/sites/default/files/the-polar-night.pdf



My request was due to my misconception that the polar circles were based on some definition of the rise/set time of the sun, not pure geometry. From that point of view you can neglect my request.



Ones again thank you for your answer, and for making the best mapping app out there!

BR

/Jens