Probably a simple question, with a simple answer..
Why is it that the waxing moon is always further south (ie: directly overhead down under) but the waning moon is always further north (low in the north for us downunder)?
Is it due to the tilt of the earth, or the elliptical orbit of the moon?
Interesting link Slice, but I'm not really sure it answers Mikes question. It only
talks about positions and how they relate to seasons. It makes no reference
to Earths axis tilt in relation to the orbital plane of the moon. Yes mike I reckon
you are correct, I think there is a difference of 5 or 6 degrees either to our
polar axis or the orbital plane cant remember which one. Perhaps someone
else can give the details...
I think part of the story is that the moon travels along the ecliptic, which is tilted at 22 degrees so it's altitude changes all the time. Not sure about any other effects as well...
Interesting link Slice, but I'm not really sure it answers Mikes question. It only
talks about positions and how they relate to seasons. It makes no reference
to Earths axis tilt in relation to the orbital plane of the moon. Yes mike I reckon
you are correct, I think there is a difference of 5 or 6 degrees either to our
polar axis or the orbital plane cant remember which one. Perhaps someone
else can give the details...
regards,CS
np Rob, It depends on what you know of the longterm lunar cycles,(like the 18.5 years cycle)
2006 is the next major standstill which means the moon will reach it's maximum declination and the fortnightly variances in moonset/rise positions are greater
more info for you .... http://www.worldastrology.net/articles/standstill.html
yes it's from an astrology site ,just skip any dribble .
Or a quicker explanation
"At what is called the Major Lunar Standstill, the moon reaches its maximum northern and southern rising points on the horizon. Solstices of a kind, though this analogy is not really accurate. In the year of a major standstill it is the winter full moon which achieves the northerly rising extreme, and the summer full moon the southerly extreme. Also in a major standstill year, the arc of the moon across the sky can vacillate quite rapidly between being very high at times, to little more than skimming the horizon at others — a very dramatic and noticeable phenomenon, especially at higher latitudes. This is because in a single month in a Major Standstill year the moon’s orbit carries it well above and well below the ecliptic.
"At the Minor Standstill year, nine years and a few months later, the winter full moon rises as far south of the midsummer sun rise Position as it ever does while the midsummer full moon rises as far north of the midwinter sunrise position as it can. So the spread of the horizon between rising and setting positions is the narrowest that occurs."
I sent a message to geoscience Aust. and even though this phenomenom was outside of there observational brief I was sent a couple of links which after clicking to afew other links from that one led to to this one:
which after staring aimlessly at it for about half an hour started to make some sense.
Apparently the moons precessional cycle moves in an 18.6 year cycle much quicker than the earth's. Anyway at the time of major standstill the moons descending and ascending nodes, where it crosses the ecliptic on its way south and then 2 weeks(approx) later north, coincide with a spring/vernal equinox the moon's full 5 degree inclination to Earth adds and then subtracts the the Earth's 23.5 degree to its inclination to the ecliptic thus bringing about the very high southern position at one point in the cycle and the very low northern in the same lunar month. The moon rises very gradually further to the west each night. until this cycle then repeats
Now at this stage I only think I understand this so check it for yourself and if you can make more sense please let me know.
there is an excellent british doco that either the abc or sbs played a number of times in recent years - it was about the ancient celts being a matriarchal society that worshiped the moon - not the sun as previously believed - and stonehenge and the famous scottish mound one - were actually being built more around worshipping the moon than the sun - EDIT: i should of said - is a general astronomical observatory - but more a lunar observatory) for the life of me I cant find its name on the web
but it was very much about this topic and the standstill years and the cycle - the standstill years being of special significance to them -and that stonehenge was made to highlight the standstill years in the cycle - the sun wasnt the main interest at all
it had many great animations dealing with the cycles - very educational!
from memory they talked about the moon bobbing up in down in its orbital plane like in a wave situ (I think the earth bobs up an down as well)
not being a big moon worshipper i have to concede i havent taken a great interest in this cycle much
Last edited by fringe_dweller; 21-11-2005 at 03:54 PM.
just out of interest, i think - from memory - there is an even bigger cycle which contains the smaller cycle - and every 200 years???? or so the moon is at a standstill for a whole cycle??? and that was of great interest to them
Stonehenge supposedly covers most of the lunar cycles including the less obvious of 80 odd years and the 400 odd year cycles ,I think. Quite a feat for primitive man with a limited lifespan of half of ours. Though the Mayans topped them by predicting cycles over milleniums.
Though the Mayans topped them by predicting cycles over milleniums.
so I wonder whats gonna happen on December 21, 2012 then hehe
seriously, they were amazing astronomers werent they!! first to study and chart dark matter too - i think
&thanks! 400 year cycle is the one your right again! - I'm impressed!
I'm getting a headache from all this lunar standstill stuff. I'd like to make an attempt to simplify an answer to what is a very interesting observation/question you raised.
If you look at the yearbook at the declination of the Moon, say comparing those of the First Quarter (waxing) to the Last Quarter (waning) the Moon is idea much further south when waxing compared to waning, in the second half of this year. In the first half, it is reversed - the waning period is further south.
As mentioned by others below (above?) the Moon's orbit is tilted by 5 degrees to the Earth's and because the ecliptic varies by + 23 to -23 degrees the Moon can go up to +28 to -28. The key to this whole discussion is that the Moon's orbit, including it's tilt is fixed in space (centred on the Earth ofcourse) - like the NCP continues to point to the same location near Polaris no matter where the Earth is in its orbit. In June the Full Moon happened to be south of the ecliptic with New Moon, North. In December the Earth is now on the opposite side of its orbit and the Full Moon is north with New - south. They have reversed. This same effect would then follow for the periods of waxing and waning. This is roughly the pattern it will follow for every year but because the Moon makes about 12 and a half orbits in a solar year the dates for the lunar phases (where the Moon is in its orbit for any particular date) will vary a lot from year to year.
This applies for any year. The lunar standstill, extremes of declination, will just make this effect a little more extreme or obvious.
Yep nicely answered Glenn - Mike you asked a tricky question to give a short answer too but Glenn has done it beautifully thanks I have a better grip on it now as well
just thought i would add - I know a lot of people have SN including you Mike? - I use the now old 4.5.2 pro
it has a neat feature that allows you to graph varying aspects of orbits - including the altitude of some heavenly bodies with regard to your location. it is not without bugs I suspect - but seems roughly right?
all i am saying is you can check easily the varying altitudes over a period of time - I assume you are mostly interested in imaging circumstances Mike?
EDIT: I notice the altitude figures are hard to see in this reduced and shrunk for the web giff - the highest one on the left is indicating 50 deg whilst the next one down says 20 deg then 10>5>2
Last edited by fringe_dweller; 24-11-2005 at 06:59 PM.
For those with access to foxtel - It appears the doco I mentioned in this thread ('Stonehenge Rediscovered') is on the national geographic channel this coming sat, 1st april at 7:30 PM - dunno if that is just eastern time, check your guides to be sure, and they do repeat these shows as well usually.
The ecliptic is inclined at 23.5 degrees from the equator, so each day the ecliptic appears to wobble +/- 23.5 degrees.
The lunar orbit is inclined at about 5 degrees from the ecliptic. So when the lunar orbit offset is in phase with the ecliptic offset, the lunar orbit appears to wobble +/-28.5 degrees. When it's out of phase, the daily lunar "wobble" (in declination) is only +/- 18.5 degrees.
Mike, at present you observations are correct. In about 6 months time they will be the other way around, but in the long term it will change as both the axis of the earth and the axis of the lunar orbit precesses.
Just watched said show on nat geo - have to say i remember it better now, and when i saw it on abc years ago, it was an hour long each, two part doco. this version seemed to be a dumbed down shortened/condensed version, maybe a case of repackaging to re-attract new buyers.
There was a number of graphics missing from this one for sure, they went heaps more into the cycles of the moon in great detail, with lots of juicy graphics, including the 400 yr cycle - that was the big finaly from what i rememeber when i saw it last.
oh well sorry! economics has triumphed again! when it finished tonight there was no mention of a second episode!? and there is none in the foxtel book I can find for this month - weird!
,just skip any dribble .
so check it for yourself and if you can make more sense please let me know. 
hehe
