Navigator wrote:

Ahh Nutation? Are you perchance an astronomer?

Nope. I took an interest in prehistoric sites for a few years (less so now),
and spent some time looking into their putative astronomical alignments.
Aside from a load of solar stuff, it would seem that there was an interest
in lunar things as well.

I dicovered the nutation period quite by chance after using a planetaruim
program to animate the view of the sky from a site near me, looking in a
southerly direction. The putative alignment was too far south to be the sun
at winter solstice, and stellar observations at the horizon were discounted
due to difficulty of seeing stars through that much atmosphere, so that left
a lunar alignment as the likely candidate. As the animation ran, I noticed
that the most southerly moonrise was moving further south, approaching the
putative alignment. As it got close, I stopped the animation at each
southern standstill and noted the azimuth. Eventually, it reached a point
where it started moving north. I ran the cycle right through until it went
fully south again.

I ended up doing a bunch of reading in an effort to gain some understanding
and found out that I'd been observing the effects of the nutation period.
The site in question would appear to be aligned towards the major southern
standstill.


--
Wally
www.forthsailing.com
www.wally.myby.co.uk

"Wally" wrote in message

| I dicovered the nutation period quite by chance snip the really cool
techno talk

WAY TO GO WALLY!!!!!!!

You Tell'em!

CM

Capt. Mooron wrote:

WAY TO GO WALLY!!!!!!!

You Tell'em!

:-)



--
Wally
www.forthsailing.com
www.wally.myby.co.uk

Wally wrote
N1EE wrote:

I find it handy to be able to judge high tide
by looking at the moon. I can add or subtract
to estimate when the next high or low tide will
be.

2004-05-04 11:42 PM EDT 8.21 feet High Tide

2004-05-05 5:44 AM EDT Sunrise
2004-05-05 6:06 AM EDT Moonset

You will note that the time of high tide slips
about 50 minutes every day and the interval
between high tides is about 12.5 hours.

A quick scan at my local data suggests slightly less slippage (30-40
minutes), but I'm not sure how reliable the info is. Did you use software
to
derive your numbers?

I study xtide and tables periodically. I see some variations with
what I observe. Generally, I tend to round off numbers. I don't
think it is critical if I'm off a few minutes. Especially since something
like rainfall seems to make a huge difference on our river.

"Bart Senior" wrote in message
. net...
Moonrise 4 pm local time
Moonset 4 am local time

Approximately when is high tide? [ 1 pt ]

I've no idea!


Cherbourg is almost due south of Portsmouth, by about 70 miles. Their
Moonrise/set times will be almost identical. However, there is a 3 hour
difference in their HW times.

One lash for asking a silly question.


Regards


Donal
--

"Donal" wrote in message
...

"Bart Senior" wrote in message
. net...
Moonrise 4 pm local time
Moonset 4 am local time

Approximately when is high tide? [ 1 pt ]

I've no idea!


Cherbourg is almost due south of Portsmouth, by about 70 miles. Their
Moonrise/set times will be almost identical. However, there is a 3 hour
difference in their HW times.

One lash for asking a silly question.

Its not a "silly question," its a trick question, which can't be answered with
one more piece of information. The key is that every sailor should know the
Establishment (or Lunitidal Interval) for their home port, and others they
frequent. Do you know yours?

"Jeff Morris" wrote in message
...
"Donal" wrote in message
One lash for asking a silly question.

Its not a "silly question," its a trick question, which can't be answered
with
one more piece of information. The key is that every sailor should know
the
Establishment (or Lunitidal Interval) for their home port, and others they
frequent. Do you know yours?


I'm not sure that there is only one piece of information missing!!


All I need to know is that when there is a full, or new, moon the HW will be
around 13:00.



Regards


Donal
--

"Donal" wrote in message
...

"Jeff Morris" wrote in message
...
"Donal" wrote in message
One lash for asking a silly question.

Its not a "silly question," its a trick question, which can't be answered
with
one more piece of information. The key is that every sailor should know
the
Establishment (or Lunitidal Interval) for their home port, and others they
frequent. Do you know yours?


I'm not sure that there is only one piece of information missing!!


All I need to know is that when there is a full, or new, moon the HW will be
around 13:00.

Well, there are a few other details that aren't stated, like the presumption the
tides are semi-diurnal.

If you know the times of moonrise/moonset then the relationship between lunar
noon (the midpoint of rise and set) and high tide is relatively fixed. Thus,
the relationship you observe about the time of high tide and the state of the
moon can be used throughout the month.

I'm assuming you're talking about Portsmouth. If so, you should double check
your understanding of the tides. Full Moon last occurred on about 5 hours ago,
May 4 at 9:35 pm BST. High tide was at 12:06 am on May 5.

"Donal" wrote in message ...
"Bart Senior" wrote in message
. net...
Moonrise 4 pm local time
Moonset 4 am local time

Approximately when is high tide? [ 1 pt ]

I've no idea!


Cherbourg is almost due south of Portsmouth, by about 70 miles. Their
Moonrise/set times will be almost identical. However, there is a 3 hour
difference in their HW times.


Dont feel bad, Clearlake varies from 6-8 hours difference from
Galveston only 35 mile from here, then tayor lake cut is an hour or so
off of the clearlake cut. And the differences change all the time.
Lucky we usually only have one high and one low a day.

Joe


One lash for asking a silly question.


Regards


Donal
--

"Wally" wrote in message
...
Navigator wrote:

Excellent informative answer at last.

Thanks.


Just to add to your post, at the
equator I think the moon takes about 12 1/2 hours from rise to set.

I think I pretty-much covered that. :-)

Obviously, Nav didn't read your entire post.


Top marks Wally (for an informative post). I give myself 2/10 for
comprehension, but I will read it again.



Regards


Donal
--