This is the broadest possible overview for those who are unfamiliar with how the motions of the Earth fit in with human timekeeping and although it is an injustice to those people who created the system we use today, the overview is much better than none at all. There is no stopping to differentiate between the original geocentric astronomers and their observations from the later heliocentric astronomers who worked off the idea that the Earth moves between Venus and Mars around the Sun so readers today don't concern themselves with the level of knowledge of any given era as this will be taken for granted in order to move the story along.

As the Earth moves through space in its circuit around the Sun,certain stars lying on or near the same plane as the Earth's orbital motion are temporarily lost behind the Sun's glare. The older astronomers marked the passage as the Sun through the constellations (hence birth signs) but for purposes of this story it is better to consider the apparent motion of the stars behind the Sun due to the orbital motion of the Earth -

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

The anchor for the Lat/Long system originally was based on the appearance of one particular star as the orbital motion of the Earth placed the star just far enough to one side of the Sun one morning, That star was the brightest one in the celestial arena known as Sirius and can be seen on the bottom left of the image -

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

".. on account of the procession of the rising of Sirius by one day in the course of 4 years,.. therefore it shall be, that the year of 360 days and the 5 days added to their end, so one day shall be from this day after every 4 years added to the 5 epagomenae before the new year" Canopus Decree 238 BC

Unbeknownst to themselves, what the Egyptians were actually doing was defining the Earth's orbital position around the Sun using the seasonal appearance of a star as a gauge and the number of rotations that fit inside an orbital circuit, in this case 1461 rotations for 4 orbital circuits which breaks down into 365 1/4 rotations to one orbital circuit.

This is the founding principle where one 24 hour day keeps in step with one rotation of the Earth and the basis of the Lat/Long system along with the reason why the extra day and rotation is introduced in order to keep the Earth's position in space fixed by the number of rotations,at least to the nearest rotation.

The next step is the process which equates the 'average' 24 hour day with 'constant' rotation insofar as the average 24 hour day substitutes for constant rotation through 360 degrees in that period.

Apologies,the correct image is reproduced.


On Saturday, January 3, 2015 8:14:28 AM UTC-8, Gerald Kelleher wrote:
This is the broadest possible overview for those who are unfamiliar with how the motions of the Earth fit in with human timekeeping and although it is an injustice to those people who created the system we use today, the overview is much better than none at all. There is no stopping to differentiate between the original geocentric astronomers and their observations from the later heliocentric astronomers who worked off the idea that the Earth moves between Venus and Mars around the Sun so readers today don't concern themselves with the level of knowledge of any given era as this will be taken for granted in order to move the story along.

As the Earth moves through space in its circuit around the Sun,certain stars lying on or near the same plane as the Earth's orbital motion are temporarily lost behind the Sun's glare. The older astronomers marked the passage as the Sun through the constellations (hence birth signs) but for purposes of this story it is better to consider the apparent motion of the stars behind the Sun due to the orbital motion of the Earth -

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

The anchor for the Lat/Long system originally was based on the appearance of one particular star as the orbital motion of the Earth placed the star just far enough to one side of the Sun one morning, That star was the brightest one in the celestial arena known as Sirius and can be seen on the bottom left of the image -


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




".. on account of the procession of the rising of Sirius by one day in the course of 4 years,.. therefore it shall be, that the year of 360 days and the 5 days added to their end, so one day shall be from this day after every 4 years added to the 5 epagomenae before the new year" Canopus Decree 238 BC

This is great reading especially for the technically challenged like me. With my style of lake boating its more like " hey, let's go that away!"

Keep it coming though. This is all good to know...

On Monday, January 5, 2015 6:09:51 AM UTC-8, Tim wrote:
This is great reading especially for the technically challenged like me. With my style of lake boating its more like " hey, let's go that away!"

Keep it coming though. This is all good to know...

Although the Egyptians knew nothing of daily rotation and the orbital motion of the Earth around the Sun, they realized that they could not base their year on a constant stream of 365 days. The flooding of Nile on which their culture depended coincided closely with the annual appearance of Sirius one morning hence their awareness of the brightest star in the celestial arena for practical reasons and the fact that it skips an appearance by one day after 4 years. In dynamical terms, the additional 24 hours represents the orbital distance the Earth needs to travel to bring Sirius back into view or what now has become the February 29th rotation. We omit 6 hours of orbital motion each non leap year as we gauge our day solely by daily rotation and this accumulates to roughly 24 hours of missing orbital distance at the end of 4 orbital circuits and 4 years.

It isn't really possible to continue with the narrative without an explanation which contains the leap day rotation and what it represents in dynamical terms. Perhaps another could explain it better and I have no objections to this however the facts will remain roughly the same.

The maritime tradition, much like astronomy, is among the most noble and ancient human endeavors in terms of sophistication so that people generally don't think of their ancestors in terms of primitive but rather look for the roots of contemporary traditions in older methods and insights. The rules governing navigation from boats to aircraft are one thing but the timekeeping systems on which navigation is based in something else and this requires some knowledge of the Earth's daily and orbital cycles.

Gerald, it's all amazing isn't it?

On Mon, 5 Jan 2015 07:48:20 -0800 (PST), Tim
wrote:

Gerald, it's all amazing isn't it?

===

It certainly is. Two years ago we visited the Mayan pyramids in
Chichén Itzá, Mexico. It turns out that the ancient Mayans were also
keen observers of celestial phenomena and had an onsite observatory
dedicated to those observations. They were aware of planetary
motions and relative orbits around the sun, including the fact that
Mars and Mercury were farther from the sun than Earth, and that Venus
and Mercury were closer. They also had a very accurate calendar
which took leap years into account. All of that was more than a
thousand years ago.

Speaking of pyramids its my understanding the the 4 corners were at a true north south east and west ane with recent technology it's been proven that they were off byaybe a degree or so.

On Monday, January 5, 2015 7:48:22 AM UTC-8, Tim wrote:
Gerald, it's all amazing isn't it?

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

To recap, when the Egyptians saw Sirius appear one morning after an absence behind the glare of the Sun for a few months they knew it would appear again 365 days later, yet again after another 365 days and then again on the third cycle of 365 days but on the fourth 365 day cycle Sirius was nowhere to be seen. It would appear the next day hence the extra rotation that we know as February 29th.

Each non leap year the Earth falls behind in position by 6 hours of orbital motion which accumulates to 12 hours after the second 365 day day cycle,18 hours after the third cycle and a full 24 hours on February 28th of a leap year. The extra rotation corresponds to 24 hours of orbital distance the Earth travels so that it completes 4 full orbital circuits using 1461 rotations as a gauge. This in turn reduces to 3651/4 rotations per circuit.

The next step is a fairly intricate one as the 24 hour day makes an appearance within this framework of 365/366 days.

On Mon, 5 Jan 2015 07:48:20 -0800 (PST), Tim
wrote:

Gerald, it's all amazing isn't it?

And also amazing is that, according to some, it's all a random
occurrence from a big explosion.

Wow.

On Monday, January 5, 2015 6:10:43 PM UTC-8, John H. wrote:
On Mon, 5 Jan 2015 07:48:20 -0800 (PST), Tim
wrote:

Gerald, it's all amazing isn't it?

And also amazing is that, according to some, it's all a random
occurrence from a big explosion.

Wow.

The words 'average' and 'constant' come into play at this juncture for the 'average' 24 hour day substitutes for 'constant' rotation at 15 degrees per hour or once in 24 hours. For instance, the average flow of a liquid through a pipe is the same thing as the constant flow of liquid through the same pipe however the timekeeping system uses 'average' as a starting point.

When accurate clocks started to emerge in the 17th century it was already known that with each sweep of the Sun across the observer's meridian, the total length of the day regardless of hemispheres varies from noon to noon. As each day corresponds to another rotation, a certain value was attached to each day to equalize it to a 24 hour average -

"Draw a Meridian line upon a floor and then hang two plummets, each by a small thread or wire, directly over the said Meridian, at the distance of some 2 feet or more one from the other, as the smallness of the thread will admit. When the middle of the Sun (the Eye being placed so, as to bring both the threads into one line) appears to be in the same line exactly you are then immediately to set the Watch, not precisely to the hour of 12 but by so much less, as is the Equation of the day by the Table." Huygens

http://adcs.home.xs4all.nl/Huygens/06/kort-E.html

So what readers have is one 24 hour day following the next 24 hour day, Monday turning into Tuesday,Tuesday into Wednesday and so on with the fact that each day corresponds to one rotation. The average 24 hour day then substitutes for the notion that the Earth's rotation is constant at a rate of 1 Degree per 4 minutes, 15 Degrees per hour and a rotation of the planet's 24901 circumference in 24 hours including the February 29th rotation.