Gerald Kelleher wrote:
On Sunday, January 4, 2015 10:12:13 AM UTC-8, KC wrote:
On 1/4/2015 11:51 AM, Gerald Kelleher wrote:
On Sunday, January 4, 2015 8:35:33 AM UTC-8, Wayne. B wrote:
On Sun, 4 Jan 2015 07:06:49 -0800 (PST), Gerald Kelleher
wrote:

Having established the original method by which humans came to
understand how the appearance of a star defined the Earth's orbital
position around the Sun and the number of times it turns within the
confines of that orbital circuit using an extra day and rotation over
a 4 year period and 4 orbital circuits, the use of the average day
and modern timekeeping comes into view. No better person than the
great John Harrison to explain the principles -

"The application of a Timekeeper to this discovery is founded upon the
following principles: the earth's surface is divided into 360 equal
parts (by imaginary lines drawn from North to South) which are called
Degrees of Longitude; and its daily revolution Eastward round its own
axis is performed in 24 hours; consequently in that period, each of
those imaginary lines or degrees, becomes successively opposite to
the Sun (which makes the noon or precise middle of the day at each of
those degrees and it must follow, that from the time any one of
those lines passes the Sun, till the next passes, must be just four
minutes, for 24 hours being divided by 360 will give that quantity;
so that for every degree of Longitude we sail Westward, it will be
noon with us four minutes the later, and for every degree Eastward
four minutes the sooner, and so on in proportion for any greater or
less quantity. Now, the exact time of the day at the place where we
are, can be ascertained by well known and easy observations of the
Sun if visible for a few minutes at any t
ime
from his being ten degrees high until within an hour of noon, or from
an hour after noon until he is only 10 degrees high in the afternoon;
if therefore, at any time when such observation is made, a Timekeeper
tells us at the same moment what o'clock it is at the place we sailed
from, our Longitude is
clearly discovered." John Harrison

So here we have the 24 hour day linked to the passage of the Sun
across the meridian each day where one rotation and one day always
keep in step and especially February 29th which represents the older
astronomical achievement that pins the Earth to its orbital position.

The next explanation is intricate but if readers can follow the
principles so far that anchor the 24 hour day to rotation there is
little that can go wrong understanding the next step which ties the
Lat/Long system to the 24 hour AM/PM system.

==
Good grief, we've been dealing with imaginary boats on this group for
years. Now we have to deal with imaginary lines also? I've seen
those lines and they are just as real as Harry's boats.

What you may take for granted in a joking way would have been a serious
issue at one stage in history -

http://en.wikipedia.org/wiki/Scilly_...saster_of_1707

The connection between the Lat/Long system along with timekeeping and
how it meshes with planetary daily and orbital dynamics has never been
explained properly hence this thread.

Anyone with the confidence of a skipper would have no problem so far
with the explanation but we are sailing into stormy conceptual waters
soon before returning to calmer waters of clear and proper perspectives.


I am guessing most of this is way beyond my pay grade...

Absolutely not. The only assumption I make is that people are interested
in how the planetary daily and orbital cycles are the basis for
timekeeping such as defining the Earth's orbital position in space by the
appearance of a single star and the number of times the planet turns
within an orbital circuit.

I don't mind the lighthearted poking about imaginary lines however the
foundations of navigation using timekeeping developed along a specific
path and involves key observations ,some of which were made in antiquity.

Until there was a dependable shipboard clock, longitude was not really able
to be calculated while at sea.