Tricky Date Calculations

[uruludu]

Can anyone answer either of the following:

1. How would I craft a Calculation that returns every Thursday date?

2. How about a Calculation that returns a sunrise/sunset times associated with that particular date? Or would I have to manually construct 365 records?

[BobWeaver]

This formula will find the dates of the Thurday for the given year and week:

Date(1, 1, Year)+5-DayofWeek(Date(1, 1, Year)) + 7*(WeekNumber-1)

For sunrise and sunset times see the following:

http://www.moonstick.com/sunriseset.htm

[rdhaden]

This guy will sell you step-by-step instructions on how to calculate sunrise/sunset with longitude, latitude, and date.

http://www.weatherimages.org/latlonsuncontact.html

[rdhaden]

Having some free time on my hands, I thought I'd try to adapt sunrise/sunset calculations I found on the web to Filemaker. I had a problem, though, because while there is an atan function, there's no asin function. Trig was never my strong suit, so I don't know if there's a way to manually get asin.

[BobWeaver]

I started to do the same thing, but haven't had time to get it finished because I had to get back to another job.

Anyway here is a formula for asin:

asin(x) = atan(sin(x)/sqrt(1-(sin(x)*sin(x))))