No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital period.

Cheers

Jeff Morris wrote:

"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 ..."

Sounds more like you don't know what you're talking about.



"Navigator" wrote in message
...
No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital period.

Cheers

Jeff Morris wrote:

"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 ..."

Are you saying that the peiod between rise and set is fixed?

Cheers

Jeff Morris wrote:

Sounds more like you don't know what you're talking about.



"Navigator" wrote in message
...

No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital period.

Cheers

Jeff Morris wrote:


"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 ..."

Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur, and no
reason why it can't happen from 4pm to 4am.

Now you can claim that you were "trying to get people thinking about something"
but I claim you have no idea about lunar noon and it relationship to the tides,
and that you had some bizarre notion that a 12 hour duration was not possible.


"Navigator" wrote in message
...
Are you saying that the peiod between rise and set is fixed?

Cheers

Jeff Morris wrote:

Sounds more like you don't know what you're talking about.



"Navigator" wrote in message
...

No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital period.

Cheers

Jeff Morris wrote:


"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 ..."

Jeff Morris wrote:
Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur, and no
reason why it can't happen from 4pm to 4am.


Yes, but is the period from rise to set at a fixed location constant?
And yes I'm trying to get some thinking going.

Cheers

After you've thought about it a bit, you can report back.


"Navigator" wrote in message
...


Jeff Morris wrote:
Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur,
and no
reason why it can't happen from 4pm to 4am.


Yes, but is the period from rise to set at a fixed location constant?
And yes I'm trying to get some thinking going.

Cheers

So you don't know the answer?

Cheers

Jeff Morris wrote:

After you've thought about it a bit, you can report back.


"Navigator" wrote in message
...


Jeff Morris wrote:

Are you claiming its broken?

There are a number of factors that determine the time between moonrise and
moonset. However, there is no reason why a 12 hour duration can't occur,

and no

reason why it can't happen from 4pm to 4am.


Yes, but is the period from rise to set at a fixed location constant?
And yes I'm trying to get some thinking going.

Cheers

Navigator wrote:

No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital
period.

Not so much a side-step, as a stumble.


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

C'mon you can try better than that.

Cheers

Wally wrote:

Navigator wrote:


No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital
period.


Not so much a side-step, as a stumble.

Navigator wrote:

No, I'm trying to get people to think about the relationship between
altitude and period between rise and set for a fixed lunar orbital
period.

Not so much a side-step, as a stumble.

C'mon you can try better than that.

Given that the moon doesn't spend each day jumping up and down like a
bouncing ball, it wouldn't be too far off the mark to say that its altitude
is a function of the the azimuths of its rise and set, and the observer's
latitude. In other words, its apparent path across the sky is largely due to
the rotation of the earth - like that of the sun.

They key thing about the sun is that its altitude for a given azimuth
changes from day to day due to the obliquity of the ecliptic - the plane of
the equator is different from the plane of the earth's orbit around the sun.
This, combined with the earth spinning on its axis, results in the sun's
rise and set azimuths changing daily and producing summer and winter
solstices, and spring and vernal equinoxes. At the equinoxes, the sun is
passing over the equator (the intersection of the equatorial and solar
orbital planes is in the direction of the sun) and, to the observer on
earth, it appears as though the obliquity of the ecliptic is zero, resulting
in the sun's rise/set being exactly due east/west. Anyone who cares to sit
on a hill for a long time will notice that this cycle is yearly.

A notable aspect of the moon's orbit is that it, too, isn't parallel to the
plane of the equator. For the observer, this is manifest as a series of
sun-like solstices and equinoxes, but with a much shorter period - monthly.
Each month, the moon has a northern and southern solstice (or standstill) ,
and twice passes over the equator midway between these, once when going from
the northern to the southern standstill, and vice versa.

The relationship between rise and set azimuths and altitude (at zenith) is
important insofar as the earth doesn't speed up and slow down during its
axial spin. Further, the altitude of the moon is lower when the rise/set
azimuths are closer to south (for the northern hemisphere). In other words,
when moonrise is towards the north, it takes a longer path across the sky
than it does when moonrise is towards the south. If the earth's rotation
speed is constant, then it must follow that the moon takes more time to
traverse the sky with a northerly rise point than with a southerly one. So,
over the period of one month, the time taken for the moon to traverse the
sky varies from day to day.

As I said earlier, if moon rise/set are due east/west, the time to traverse
the sky is about 12 hours. It isn't *exactly* 12 hours because the moon is
orbiting the earth, but it is *about* 12 hours, because it's orbiting the
earth *slowly*. To render some precision to the description: If I stand at
the Greenwich Observatory and note the moon's azimuth at midnight tonight,
and then wait for it to pass through that azimuth tomorrow night, it'll take
nearly an hour for the moon to 'catch up' - nearly 25 hours.

For an east/west rise/set, the nominal time taken to traverse the sky is 12
hours - half the period of the earth's axial rotation. However, since the
moon takes time to catch up, the time to traverse would be longer - I guess
about 12.5 hours (half the earth's rotation period, plus half the moon's
'catch up' time). It would seem that moonrise at the northern standstill
would entail a greater proportion of the moon's catch up time being added
because the moon is visible for a greater portion of the earth's rotation
period, and vice versa for moonrise at the southern standstill. A true 12
hour traverse of the sky by the moon would consequently entail a rise/set a
little to the south of east/west to account for the delay in the moon
catching up to reach the same azimuth.


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