jerrytug
N/A
And at 1800 GMT,the Moon is due south at the 1st quarter or 3rd. From a London point of view. Handy if true. Should it be passed on as a useful tip or is it a yet another tall tale?
"The full moon is due South at midnight."
- Thread starter jerrytug
- Start date
macd
Active member
Simple geometry: if the full moon is due south, the sun is due north (albeit unseen). But 'midnight' is solar midnight, which will almost never be exactly the same as local time. But within the limited accuracy of observations by the unaided eye, it has some use.
Similar geometry works for the half moon (i..e at the "quarters") in the way you've described, except that on the waning quarter the moon is due south at 0600, not 1800.
Essentially, it's solar navigation of a sort: the moon is simply telling you where the sun is.
Similar geometry works for the half moon (i..e at the "quarters") in the way you've described, except that on the waning quarter the moon is due south at 0600, not 1800.
Essentially, it's solar navigation of a sort: the moon is simply telling you where the sun is.
Last edited:
DJE
Well-known member
Sounds believable for a full moon as it is directly opposite the sun in the sky. But the OP said 1st or 3rd quarter. How does that work?
AndrewB
Well-known member
True, but only approximately, at either 0600hrs or 1800hrs on the day of the quarter moon.* The moon will only be above the horizon (and therefore visible) at one of those times.
For example, next (third) quarter occurs on Jan 16th. At 0600hrs the moon will be at 185°, that is, just west of south, as seen from London.
The advantage of the full moon tip is that a full moon is obvious, and one can judge approximate south from the point at which it is highest in the sky regardless of where one is (north of the tropics), without needing a watch.
*Note: NOT at the exact time of the quarter moon.
For example, next (third) quarter occurs on Jan 16th. At 0600hrs the moon will be at 185°, that is, just west of south, as seen from London.
The advantage of the full moon tip is that a full moon is obvious, and one can judge approximate south from the point at which it is highest in the sky regardless of where one is (north of the tropics), without needing a watch.
*Note: NOT at the exact time of the quarter moon.
Last edited:
DJE
Well-known member
I was geting the two posts mixed up. Quarter moon at 18:00 and full moon at midnight makes sense.
GeorgeLlewellin
Member
Thread drift
In a similar vain, I am sure you solar navigators can answer a question for me.
What are the bearings of sunrise and sunset on the longest and shortest days, preferably from Milford Haven?
Many thanks, George
In a similar vain, I am sure you solar navigators can answer a question for me.
What are the bearings of sunrise and sunset on the longest and shortest days, preferably from Milford Haven?
Many thanks, George
awol
Well-known member
macd
Active member
DJE: sorry: you'll see I've since edited my post having finally woken up. The grog here is a killer. Hope the revision makes more sense to you. Essentially, the moon is simply acting as an indicator of where the sun is. And since earth time is dictated by the sun (even when you can't actually see it), the moon informs this.
The half moon tells you that the sun is at right angles to your line of sight to the moon. So when the moon is at it's zenith (which is due South) that would place the sun roughly on the horizon: i.e. 0600 or 1800. Of course there's often an easier way to get a sense of time from this phenomenon: it's called sunrise/sunset.
Last edited:
macd
Active member
GeorgeLlewellin
Member
DanTribe
Well-known member
jimbaerselman
New member
Slight snag is that exact full moon may not be at midnight - so the guesses are going to be in error by up to 6 degrees . . .