On Sunday, January 4, 2015 9:55:04 AM UTC-8, Wayne. B wrote:
On Sun, 4 Jan 2015 08:51:32 -0800 (PST), 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
time
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.

===

As a self proclaimed expert in these matters, I assume you have also
read "Longtitude" by Daba Sobel and "The American Practical Navigator"
by Nathaniel Bowditch. There is a wealth of information in both.

In this case, anyone who wishes to follow the narrative must also reason from observations made possible by 21st century tools such as imaging and graphics.

It is crucial that the founding principle of timekeeping where an extra day and rotation is added after four 365 cycles corresponding to 4 orbital circuits of the Earth around the Sun is understood thoroughly but I personally don't envisage any problem with that.

The first appearance of Sirius (heliacal rising) just far enough to one side of the Sun to be seen one morning is a line-of-sight observation as the Earth moves around the Sun and the star is periodically lost behind its glare -

https://www.youtube.com/watch?v=eeQwYrfmvoQ

http://www.gautschy.ch/~rita/archast...liacsirius.JPG

A teacher should,by right, should be capable of answering a student's question as to why February 29th as both a day and as a rotation is required much less navigators who rely on the Lat/Long system as an extension of planetary dynamics and timekeeping.

I suspect many are new to this reasoning so every incentive to give it more consideration.