NavList:

From: George Huxtable <george@hux.me.uk>
Subject: [NavList 9411] Re: Lunar longitudes, not by lunar distance.
To: NavList@fer3.com
Date: Saturday, August 8, 2009, 6:12 AM

Hanno Ix wrote, in [9382],

If I see things right, there must be a LOP which connects all locations
on Earth with a given, fixed difference DT between the meridian
passages of sun and moon.

What I meant is:

If I see things right, there must be a LOP which connects all those
locations
on Earth that have a given, fixed difference DT between the meridian
passages of sun and moon.

================

and I replied, in [9402]-

Is there woolly thinking here, I wonder?

Wherever on Earth the Moon is seen from, it's phase is the same except for
the effects of parallax, which can be corrected for. At Full Moon, it's
always very nearly 180 º from the Sun. So that's the Sun's lunar distance,
which is the same wherever on Earth it's observed from. And then the time
difference between meridian passages of Sun and Moon is 12 hours, the whole
World over. The phase of the Moon, the lunar distance, and the time
difference between meridian passages, change in step, going through a whole
cycle in a month, and at any moment in the month all are the same wherever
on Earth they are observed from. Measuring a lunar distance, or the time
between meridian passage (or even the phase, if it was possible to do that
precisely), all provide the same message: the time of the month. From that
time of the month, from the nautical tables, we could deduce the day (if
that was needed) or, more importantly, the time-of-day, in terms of GMT. It
by comparing that GMT with the local time that we deduce the longitude.

There's no "LOP which connects all those locations on Earth that have a
given, fixed difference DT between the meridian passages of sun and moon."
At any moment that DT is the same everywhere.

===================


To which Brad Morris has responded in [9403]-

Hang on George,


Hanno has required that the moon and the other object be ON the meridian at
different times, and that the delta time between those meridian passages be
the key component.

I agree with your statement that it is the same for everybody on earth,
should that delta time not include the meridian passage.

Once the meridian passage is included however, then only ONE meridian has
that precise delta time, the meridian of observation.  As the earth rotates
and the moon changes position, then the delta time will change.

At your meridian in the UK, the delta time will be X.  By the time those
same objects individually CROSS MY MERIDIAN in the US, about 5 hours later,
the position of the moon will change by about 2.5 degrees.  Thus the delta
time between those objects on my meridian will be different!

Anyone on your meridian, independent of latitude and under the assumption
that they can see them, will get the same delta time.

===================

Response from George-

It's making my head hurt a bit, this question, but I now think Brad, and
Hanno also, have it right.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.