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Old 2011-05-06, 06:31   #1
davieddy
 
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"Lucan"
Dec 2006
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Default Time scales

Apart from the obvious fact that God created the whole world
in 7 days (albeit resting on the 7th) why does a week have 7 days
throughout the world?

David

PS what day is it today?

PPS I've heard it said that the equality
beween the periods of female menstrual cycles and lunar orbits
is "down" to more than coincidence.

PPPS To Mods: Possibly Soapbox material?

Last fiddled with by davieddy on 2011-05-06 at 07:15
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Old 2011-05-06, 07:01   #2
Raman
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Because moon takes 7 days to go from that phases
New Moon to First Quarter
First Quarter to Full Moon
Full Moon to Last Quarter
Last Quarter to New Moon
back.
It is approximate timings only. 28 days for a month?
By the way, see that different types of months over here.
What I mean that, it's actually
27.32 days for moon to go complete one revolution around Earth due west to back again - Sidereal Month
29.53 days for moon to go from one New Moon transition to that next case - Synodic Month - although it varies always rather somewhat from 29.27 days upto 29.83 days - given that this is upon average scale only
27.21 days from Ascending Node to Descending Node to back - Draconic Month - these nodes complete with a cycle around that earth once every 18 years or so
27.55 days from Perigee to Apogee to back - Anomalistic month

Note that number of days, given that exact timings between N new moons is being actually given up by using a quadratic polynomial only exactly man as usually

Last fiddled with by Raman on 2011-05-06 at 07:28
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Old 2011-05-06, 09:45   #3
davieddy
 
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"Lucan"
Dec 2006
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Default Euler/Laplace and all that

IHX for rescuing this thread from the soapbox or
"useles posts by nameless".

A few years ago, I worked out why the earth's axis of rotation
rotated in 25,000 years. Applying the same formula to the moon
(treated as a circular ring of radius 250,000 miles) it said
that its orbital axis should rotate every 18 years.

One of many reasons to enjoy maths!

David

Last fiddled with by davieddy on 2011-05-06 at 09:48
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Old 2011-05-07, 04:35   #4
cheesehead
 
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"Richard B. Woods"
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Quote:
Originally Posted by davieddy View Post
Apart from the obvious fact that God created the whole world in 7 days (albeit resting on the 7th) why does a week have 7 days throughout the world?
The primary theory is that in antiquity there were 7 "planets". See http://www.hermetic.ch/cal_stud/hlwc/why_seven.htm for a discussion.
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Old 2011-05-07, 07:39   #5
davieddy
 
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Quote:
Originally Posted by cheesehead View Post
The primary theory is that in antiquity there were 7 "planets". See http://www.hermetic.ch/cal_stud/hlwc/why_seven.htm for a discussion.
THX Richard,
but I think that article merely shows that it was not a dumb
question, albeit difficult to answer.
My gut feeling is quarters of the lunar cycle.

BTW I have never thought "nesting" the 5 platonic solids
was anything other than a truly ugly/crass way of "explaining" the
relative radius of planetary orbits.

David
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Old 2011-05-07, 08:37   #6
cmd
 
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Old 2011-05-07, 09:10   #7
davieddy
 
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Dec 2006
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As a physics teacher, I have seen the spectrum of visible light on
innunerable occasions. With the exception of indigo, why do we
(the non-colourblind) distinguish red, orange, yellow, green and blue
so clearly from the continuum?

David

PS As I'm sure you know, I have considerable experince
with 1(+) bit colour programming/rendering.

PPS Think I'll watch some now:)

Last fiddled with by davieddy on 2011-05-07 at 09:44
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Old 2011-05-07, 09:44   #8
cmd
 
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_ _.
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Old 2011-05-08, 03:38   #9
jasong
 
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cmd, the fscking RIAA blocked your video.

Guess that artist won't be getting any free advertising, huh?

Morons.
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