[RndTbl] Cron entries for sunrise and sunset

Troy Denton trdenton at gmail.com
Sun Jul 5 10:45:58 CDT 2020


>
> That's a really cool idea.  Looks like you're doing it all with math
> and no external (web) lookups?  How long does just the math way stay
> accurate?  Don't you need to account for wobble and things that may
> subtly change over time (assuming they do, I thought something did)?


Yep, it's all math-based - the calculations used "[...] are theoretically
accurate to within a minute for locations between +/- 72° latitude, and
within 10 minutes outside of those latitudes.".  That's via
https://www.esrl.noaa.gov/gmd/grad/solcalc/calcdetails.html, which is used
by "sunrise.c" (original available here
<http://souptonuts.sourceforge.net/code/sunrise.c.html>).  The explanation
claims that the calculation is valid until the year 3000!  I'm not clear if
it handles wobble and other things - the calculations are mostly a black
box for me.

Anecdotally it seems to be working fine on my box :)

You should crisp it up as much as possible and submit it to the cron
> upstream!  Has to be self-contained, clean and accurate though
> (probably).


I might do this at some point, it could use more cleanup - I have just
noticed that debian's cron package is a major version behind the upstream
as well

Thanks for the feedback!


On Sun, Jul 5, 2020 at 3:59 AM Trevor Cordes <trevor at tecnopolis.ca> wrote:

> On 2020-07-04 Troy Denton wrote:
> > A fun side project of mine - I've patched the Debian 'cron' source to
> > provide @sunrise and @sunset, similar to @reboot
>
> That's a really cool idea.  Looks like you're doing it all with math
> and no external (web) lookups?  How long does just the math way stay
> accurate?  Don't you need to account for wobble and things that may
> subtly change over time (assuming they do, I thought something did)?
>
> You should crisp it up as much as possible and submit it to the cron
> upstream!  Has to be self-contained, clean and accurate though
> (probably).
>
> Good clean code layout.  Nice.  Extra hero cookie for C.
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