by comparison this is an absolute mountain of code. here is a good one - but note that it is only so accurate for each quarter phase (...and not sure why it destroys the formatting):
function approximateMoonPhase(julianDay)
{
// from Meeus p.319
// JDE = 2451 550.09765 + 29.530 588 853 k
// + 0.000 1337 T2
// - 0.000 000 150 T3
// + 0.000 000 000 73 T4
const t = toJulianCenturiesSinceJ2000(julianDay);
const lhs = julianDay - 2451550.09765 + (-0.0001337 + (0.00000015 - 0.00000000073 * t) * t) * t * t;
return lhs / 29.530588853;
}enjoy. its from the same source as your work appears to use...
which, as someone who as implemented a ton of this stuff. its kind of a damning sentiment that we still refer to such an old book instead of learning the problem space and making better solutions... i have a whole book in me about this at some point.
Great library, super documentation and the code seems well written with lots of tests. Kudos, I will definitely check it out for my next ios project.
Thanks Otto
I bought my friends daughter a watch for her birthday. She was, like, 12 or something. I got it at Target.
And it had a moon phase dial! How about that?!
So I was determined to set it accurately for her.
To wit I started dredging through the internet. And to be completely honest, I'm not quite sure how I was doing that, having nothing but a Netcom.com shell account available to me. Perhaps I was using Lynx, or using some mail gateway, or who knows what. It wasn't no 10 seconds on Google, I'll tell you that.
In the end, I stumbled upon some code for my HP-48. Aha! This should do nicely!
Somehow, I got the code into the calculator. Did I type it in? Did I download it over Kermit? Who knows. Times were moving fast back then. Somehow, someway, however, I got that code in and calculated away.
Finally! ACCURATE results. Done with precision and math and engineering. Done Right!
To wit, I then proceeded to get the watch set properly.
And...it was a fashion watch for a 12 year old girl from Target. This may come as a shock to some, I was obviously taken aback by it, however -- the moon phase did not work. It was just a moon on a dial that moved, though some undetermined mechanism. It could not be set independently.
Oh.
Most of them are written in JavaScript only, but specifically written to be easy to port to other languages.
_=min
lphase = lambda y,m,d: _( lkp(ph,p)
for lkp in [lambda t,x: _(v for (kl,v),(kh,w)
in zip(t,t[1:]) if kl <= x < kh)]
for daynum in [lambda y,m,d: daynum(y-1,m+12,d) if m<3 else
y*365 + y//4 - y//100 + y//400 + (153*m+3)//5 + d]
for o in [daynum(y,m,d)-daynum(2000,1,6)]
for p in [o%29.53] # mean; varies significantly!
for ph in [[(0,"new"),(0.5,"waxing crescent"),(7,"first quarter"),
(8,"waxing gibbous"),(14.5,"full"),(15.5,"waning gibbous"),
(21.7,"last quarter"),(22.7,"waning crescent"),(29,"new"),
(30,None)]] )
I used this approach because most platforms supports islamic calendar.
I really like the offline first approach, and would definitely use the library when there’s a need.
Thanks for sharing!