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.

Ok, I'll give it a try -

Halfway between moonrise and moonset is 10 pm local time, which is the time of
transit of the local meridian. To this we must add the "Local Establishment" or
the "Lunitidal Interval" (actually the proper terms are "high water full and
change" or "mean high water lunitidal interval") to get the time of the next
high tide.

This was published on old charts. My 1867 Boston Harbor chart lists the
"Corrected Establishment" (average of all high water intervals) for Boston Light
as "XIh XIIm". This mean you add 11 hours and 12 minutes to the time of local
meridian passage of the moon to get the time of the next high tide.

Tides watches usually require setting the Lunitidal Interval for a particular
spot. Of course, this only works for semidiurnal tides.


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

Approximately when is high tide? [ 1 pt ]

2 pts. Great answer Jeff. an extra point for adding
worthwhile content.

Can you name two places where tides are diurnal?

What are spring and neap tides and how can you tell by
observing the moon, if a tide will be spring or neap?

Jeff Morris wrote

Halfway between moonrise and moonset is 10 pm local time, which is the
time of
transit of the local meridian. To this we must add the "Local
Establishment" or
the "Lunitidal Interval" (actually the proper terms are "high water full
and
change" or "mean high water lunitidal interval") to get the time of the
next
high tide.

This was published on old charts. My 1867 Boston Harbor chart lists the
"Corrected Establishment" (average of all high water intervals) for Boston
Light
as "XIh XIIm". This mean you add 11 hours and 12 minutes to the time of
local
meridian passage of the moon to get the time of the next high tide.

Tides watches usually require setting the Lunitidal Interval for a
particular
spot. Of course, this only works for semidiurnal tides.

The Gulf Coast is the main diurnal tide in the USA. Southeast Asia is another
area.


http://chinook.kpc.alaska.edu/~ifeeb...altidemap.html
http://www.oceanservice.noaa.gov/edu...07_cycles.html


"Bart Senior" wrote in message
.net...
2 pts. Great answer Jeff. an extra point for adding
worthwhile content.

Can you name two places where tides are diurnal?

What are spring and neap tides and how can you tell by
observing the moon, if a tide will be spring or neap?

Jeff Morris wrote

Halfway between moonrise and moonset is 10 pm local time, which is the
time of
transit of the local meridian. To this we must add the "Local
Establishment" or
the "Lunitidal Interval" (actually the proper terms are "high water full
and
change" or "mean high water lunitidal interval") to get the time of the
next
high tide.

This was published on old charts. My 1867 Boston Harbor chart lists the
"Corrected Establishment" (average of all high water intervals) for Boston
Light
as "XIh XIIm". This mean you add 11 hours and 12 minutes to the time of
local
meridian passage of the moon to get the time of the next high tide.

Tides watches usually require setting the Lunitidal Interval for a
particular
spot. Of course, this only works for semidiurnal tides.

Bart Senior wrote:

Can you name two places where tides are diurnal?

Always diurnal, i.e. only one tide per day, every day? - No. I don't
think there is one. It'd be a very rare combination of geography and
geography.

Diurnal most of the time, i.e. only one tide per day most days, with
other days showing a smaller second tide? - Lots of places. The
Aleutians and the Gulf of Mexico are two.

What are spring and neap tides and how can you tell by
observing the moon, if a tide will be spring or neap?

Spring tides are bigger than neap tides. Spring tides occur at the full
moon and at the new moon. Neap tides occur at the first and last
quarter.



BTW, I sail on a small inland lake, so this stuff is just trivia for
me. Tides schmides - the real question is which direction is the next
90 degree wind shift coming from.

--
//-Walt
//
// Sigs suck. Oh, the irony.

What location has moon rise and set 12 hours apart? If moon rise is at
4pm the next high tide here will be about 5:30pm -I think.

Cheers

Bart Senior wrote:

Moonrise 4 pm local time
Moonset 4 am local time

Approximately when is high tide? [ 1 pt ]

Navigator wrote:
What location has moon rise and set 12 hours apart?

Virtually anywhere, I'd guess - just had a look at moon rise and set for
some random locations (Glasgow, Jerusalem and Canberra), for today, and
they're all a shade over 12 hours apart. If rise/set are close to due
east/west, then the time for the moon to traverse the sky will be about 12
hours - think about the solar equinoxes, where the sun rises/sets due
east/west. I dare say this princple won't hold at extreme latitudes. The
moon passes the due east/west points twice in its mo(o)nthly cycle.


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

Wally wrote:
Navigator wrote:

What location has moon rise and set 12 hours apart?


Virtually anywhere, I'd guess - just had a look at moon rise and set for
some random locations (Glasgow, Jerusalem and Canberra), for today, and
they're all a shade over 12 hours apart. If rise/set are close to due
east/west, then the time for the moon to traverse the sky will be about 12
hours - think about the solar equinoxes, where the sun rises/sets due
east/west. I dare say this princple won't hold at extreme latitudes. The
moon passes the due east/west points twice in its mo(o)nthly cycle.


The devil _is_ in the detail and is it ever 12 hours????

Cheers

Navigator wrote:

The devil _is_ in the detail and is it ever 12 hours????

What part of 'find lunar noon' are you ignoring in lieu of trolling for
nanosecond-precise astronomical timing?


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

"Navigator" wrote in message
...


Wally wrote:
Navigator wrote:

What location has moon rise and set 12 hours apart?


Virtually anywhere, I'd guess - just had a look at moon rise and set for
some random locations (Glasgow, Jerusalem and Canberra), for today, and
they're all a shade over 12 hours apart. If rise/set are close to due
east/west, then the time for the moon to traverse the sky will be about 12
hours - think about the solar equinoxes, where the sun rises/sets due
east/west. I dare say this princple won't hold at extreme latitudes. The
moon passes the due east/west points twice in its mo(o)nthly cycle.


The devil _is_ in the detail and is it ever 12 hours????


Why not? What's the problem? Or are you making the sophomoric argument that
its very unlikely to be "precisely" 12 hours? It certainly isn't hard to find
places and times where its within a couple of minutes. Certain latitudes are
more favorable than others for this situation to exist, but there's nothing the
precludes it.

Have a go with:
http://aa.usno.navy.mil/ select "Data Services" and then "Table of
sunrise/sunset ..."