3
$\begingroup$

If I do a quick Google search for amsterdam sunrise, I immediately get the time back: 6:42 AM.

How is this time calculated?

(I mean how it is really calculated, not how Google get it, with is probably from a table. Of course I mean sunrises and sunsets in the future, not from the past. $:)$)

$\endgroup$
  • 1
    $\begingroup$ Do you know about the sunrise equation? Scroll down to the bottom. $\endgroup$ – HDE 226868 Aug 25 '16 at 20:02
  • $\begingroup$ Thanks, no. From what I read I can calculate $\omega_o = \text{acos}{(-\tan(\phi)\tan(\delta))}$ with in my case $\phi = 50^{\circ}$. How do I get the value of $\delta$ and how do I convert $\omega_o$ to HH:MM (hours and minutes)? Thanks in advance. $\endgroup$ – Kevin Aug 25 '16 at 20:11
  • $\begingroup$ For $\delta$, see here. You just need to find the solar declination of the day. $\omega_o$ is a spatial coordinate, not a length of time. For the date, you need to do a bunch of intermediate calculations, then find the Julian date. $\endgroup$ – HDE 226868 Aug 25 '16 at 20:17
  • $\begingroup$ You can use the CSPICE libraries to calculate it exactly, and USNO publishes it for a wide variety of locations, but I think you're asking: what simple equation does this so that websites can use it (or use JavaScript) without having to do super-precise calculations? $\endgroup$ – user21 Sep 1 '16 at 17:16
  • $\begingroup$ Yes, that's what I meant to ask. 🙂 $\endgroup$ – Kevin Sep 2 '16 at 11:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.