Sun position

[SAR704]

Just wondering, how do you change the position of the sun, so that it appears in the northern part of the sky coming from the east?

[Bananarama]

There was a post a couple of years back on Trainsim.com describing sun azimuth and how to improve (at the time) Railworks.

[buzz456]

Where would you be at that the sun would be in the Northern sky.

[SAR704]

I live in a country south of the equator. Unfortunately, adjusting the sun azimuth didn't work for me. Is there anything else I need to do?

[Bananarama]

If you have the original RS Cajon route, the sun azimuth is backwards making it a good place to start.

[PapaXpress]

Would this help?

http://thegradecrossing.blogspot.com/20 ... art-4.html

[nsl714]

If I could interject here a moment. I'm currently going through the timeofday files tweaking the sun and whatnot for Northern Illinois. I followed the above procedure and equation for the Azimuth. Below are my results. Both are taken at 12:00 with the camera facing straight east.

Summer



Winter



Now, that is backwards to what I would expect. (Living in the area, I am aware that the sun should be further south in the sky. The azimuth I got for summer was 56, and winter was 120. Subtracting those from 150 and dividing by 100 gave me Azimuth numbers of -0.924 and -0.289 for summer and winter respectively. For now I have just swapped the numbers in the TimeOfDay files, and that is sufficient, but I would like to know if there is some error I propagated in the calculations.

Second Question: I have tried to set up free roam activities with the 3d weather. However, the 3d weather seems to be using a different time of day bin file. Is there somewhere special where this is hiding? Would it be too inconvenient to set up perhaps a copy of the 3d weather with the appropriate sun azimuth and time of day?

Thanks,
Zach

[PapaXpress]

Not sure I follow. For summer we should see a longer shadow at noon (unless I am forgetting Astronomy 101 from 20 odd years ago).

[nsl714]

I thought that in the summer, the Northern hemisphere is tilted toward the sun, therefore the sun should be more directly overhead in the Midwestern US. Likewise, in winter, the axis of the earth should be such that the Southern hemisphere is tilted toward the sun (giving them summer and the North winter). Therefore in the Northern Hemisphere should see the sun further south in the sky during the winter. Hence my confusion as to why the sun is displaying the opposite as a result of the calculations in winter. (It looks like I didn't make that clear in my first post, that I am examining a Northern Hemisphere condition rather than a Southern hemisphere condition like SAR704 is )

[wacampbell]

(unless I am forgetting Astronomy 101 from 20 odd years ago).

I am pretty sure nsl714 is correct for Chicago area. There may be some areas close to the equator where the opposite is true.

[buzz456]

seasons.jpg

Seasons. Sun higher in the sky shorter shadows in the Summer.

[fecrails]

I have no idea how TS calculates the sun position or what variables are used and where they are stored, but I do know that the azimuth of the sun (position E of N) at any given time and date is only half of the celestial coordinates needed to define the apparent position of a celestial object in the sky. The other coordinate needed is the altitude (angular position above the horizon).

Using the U.S. Naval Observatory online calculator; on the summer solstice at Chicago, Illinois the sun will reach its highest altitude of 71.6 degrees at 12:50 local time. At that time the azimuth of the sun will be 178.2 degrees, almost due south. On the winter solstice at the same location the sun will reach its highest altitude of 24.7 degrees at 11:50 local time. At that time the azimuth of the sun will be 180.3 degrees, again almost due south.

In the above example it is plain to see two things: Yes, objects will cast a much longer shadow in the winter than they do in the summer at that location due to the sun's low apparent angle in the sky during the winter compared to summer. Secondly, the important variable that changes with the seasons is the altitude of the sun at local maximum, not the azimuth. By definition the azimuth will remain 180 degrees (the minor differences of the azimuth angle in the examples are caused by extrapolating the resulting calculation to the closest minute) at the maximum local altitude regardless of the season in the northern hemisphere. The variables that will change will be the altitude and the local time that the maximum altitude will be reached.

Azimuth would be the most important variable in defining the apparent position of the sun at times of sunset and sunrise.

Hope this helps.

[PapaXpress]

Actually Buzz helped a lot with that picture. So is TS messed up, or my blog, or both?

[nsl714]

All I can say is swapping the Azimuth values for Summer and Winter produces satisfactory results, at least at the Latitude I'm at.

[Bananarama]

So is TS messed up, or my blog, or both?

I believe the azimuth values in TS are coded backward - positive yields a negative and vis versa.