Current Moon Phase

[rumples riot]

Hey Mike, have noticed that that current moon phase indicator does not seem quite right. Visually it looks like it is at least 1-2 days out of whack. Last night we had a 3/4 gibbous moon and the indicator said 93%. Just did not look right. Anyone else notice this or am I incorrect?

[h0ughy]

I agree, but I think someone said something about this in another post somewhere!

[[1ponders]]

The other post was saying that the image of the moon is as it would be seen from the Nth hemisphere h0ughy. But I agree that the phase indicator seems to be a day or two ahead

[iceman]

hmm it doesn't quite look right..

It says next full moon is the 19th in one part, but then down below it says it's on the 20th. Maybe there's a timezone miscalculation in there somewhere.

Another moon phase calendar I found has the full moon on the Aug 19 17:53 UT, which would be August 20th here. Maybe the top section, and the bit that displays the graphic, is in the wrong timezone.

I'm sure Terry will see this thread, otherwise i'll email it to him.

[mojo]

My my. For people that didn't even realise the moon was mirrored, you sure are pedantic about the next full moon.

Ok. Here's the story with the moon phase. The rise and set times are very accurate; to within +/- 1 minute. Basically rounding errors. The moon phase, on the other hand, is not exactly right.

For instance, the next full moon is shown as 19 August (it doesn't show it, but it's at 11:42pm). The list shows it as the 20th because each phase is taken from midnight of that day, so it's just rounded up and shown it to be a full moon on that day.

The actual and correct full moon is 4 hours later on the 20th at 3:54am.

The reason for this, is that the current moon phase calculation is an aproximation without solving for Kepler's equation. I was too lazy to actually code the formula, so I used an aproximation based on the date of a full moon in 2001.

So for the people looking for hair on their palms, don't fret. I'll rewrite the moon phase to display the exact phase to within +/- 1 minute. And you'll know exactly when the next full moon will be. :computer:

Thus endeth the moonphase lesson...