The great star,a Christmas thread

Orion36

In its yearly circuit around the Sun,the orbital motion of the Earth puts certain stars behind the Sun like so -

http://www.youtube.com/watch?v=eeQwYrfmvoQ&list=PLDZvNEf3nY-6c4Db4oAcYaW1okcYgB1NR

Of all the stars in the celestial arena, the most dazzling and important astronomically and for timekeeping purposes is Sirius,a star which is lost behind the glare of the Sun for a few months until it appears just far enough to one side of the Sun to be seen one day -

http://danmary.org/tiki/show_image.php?id=30

One real observant person in antiquity noticed that Sirius did not appear after a consistent 365 day cycle but skipped a day after the 4th cycle and they wrote about this in the most endearing terms even if unaware of the dynamics behind the observation -

" on account of the precession 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, whereby all men shall learn, that what was a little defective in the order as regards the seasons and the year, as also the opinions which are contained in the rules of the learned on the heavenly orbits, are now corrected and improved" Canopus Decree ,Egypt 236 BC

What the observation that Sirius told the Egyptians (and us) is that to keep their festivals fixed to the Solstice and Equinox points they had to add an extra day after 4 years.Dynamically it is far more interesting,it tells students that when Sirius moves far enough to one side of the Sun to be seen due to the orbital motion of the Earth,it takes an extra rotation's worth of orbital motion to return our planet to the same orbital position.

When I first encountered the system buried under contemporary academic rubbish it felt like the same way O'Kelly must have felt when he discovered the roofbox at Newgrange for indeed they are linked inextricably to timekeeping and antiquity with a very contemporary slant in terms of dynamics.

This Christmas gift is to students who can now learn how many rotations fit into an orbital circuit,in this case 365 1/4 rotations to one circuit,and how it was figured out by the great people of the past,at least in terms of days in a year.

Orion36

The second part of this story is astronomical storytelling at its finest.

The morning appearance of Sirius after a few months disappearance behind the glare of the Sun fixes the Earth's position in space even though the Egyptians were unaware of the dynamics behind that astronomical event.Moving just far enough to one side of the Sun as the Earth moves through space is easily enough captured by the animated graphic and how the Egyptians would have observed the first appearance of Sirius -

http://www.youtube.com/watch?v=eeQwYrfmvoQ&list=PLDZvNEf3nY-6c4Db4oAcYaW1okcYgB1NR

http://danmary.org/tiki/show_image.php?id=30

So the dynamics behind the leap day is that it takes an extra rotation's worth of orbital motion after every 4th cycle of 365 days (1461 rotations) to return the Earth to the same orbital position in space where Sirius can be seen once more which ultimately reduces to 365 1/4 rotations to one orbital circuit . Treating it like a new puzzle and how the pieces fit together is an enjoyable experience and that holds true for all the other additions to this story.

So the next step is how those 1461 days and rotations connect to the 24 hour AM/PM system and the Lat/Long system where 15 degree difference equates to 1 hour , the Earth turns once in 24 hours and these rotations keep in step.

The difference between a sundial and a clock is that the sundial registers variations in the length of each noon cycle by the motion of a shadow across its face while the clock hands have a steady progression every 24 hours even though clock noon is fixed to the appearance of the Sun at noon.

So within each of these 1461 noon cycles that fit inside 4 orbital circumferences of the Earth (we format them and count them as three years of 365 noons and one year of 366 noons) there is a variation which was then corrected to an average 24 hour day so that the 24 hours of Monday elapse into the 24 hours of Tuesday and so on remain fixed to noon even though dynamically those noon cycles vary in their total length across the entire planet from day to day -

"Here take notice, that the Sun or the Earth passeth the 12. Signes, or makes an entire revolution in the Ecliptick in 365 days, 5 hours 49 min. or there about, and that those days, reckon'd from noon to noon, are of different lenghts; as is known to all that are vers'd in Astronomy. Now between the longest and the shortest of those days.... this is call'd the Equal or Mean day, according to which the Watches are to be set; and therefore the Hour or Minute shew'd by the Watches, though they be perfectly just and equal, must needs differ almost continually from those that are shew'd by the Sun, or are reckon'd according to its Motion. But this Difference is regular, and is otherwise call'd the Aequation" Christian Huygens

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

As 'average' and 'constant' share the same meaning,the conversion of the average 24 hour day into constant rotation at 15 degrees per hour and once in 24 hours was a brilliant development and remains so for people who can truly appreciate the sprawling history of the Longitude problem and how watches keep track of the Earth's rotation once each day.

It is a basic human right that students and adults learn not only that the Earth turns once in 24 hours but also how that value was tied to rotation via the development of the Lat/Long system and the 1461 rotations that fit inside 4 orbital circumferences of the Earth. It is a violation of human rights to insist the Earth does not turn once in 24 hours and that there is an imbalance of 1465 rotations in 1461 days as someone in the other thread announced.

It is not possible to rewrite history as the guys in the late 17th century and their followers here today try to do for it disrupts the actual history of the development of timekeeping including the choices our ancestors took in creating the system we all use day in and day out,literally.