Re: [RT] The moon cycle - how strong?

[Clyde Lee <clydelee@xxxxxxxxxx>]

Dennis,
 
The attached shows your function compared 
to the values
generated from the following 
function.
 
The following function which was 
contributed by Gary Funk
has some verbage that may be of interest to 
those who
want to know more about how the calculation 
of moon phase
is accomplished over time.
 
Note that this function goes from ZERO to 
29.xxxx rather
than from zero to one and back 
down.
 
I use this in preference to your 
implementation because
I can tell exactly which side of new/full I 
am on simply
by looking at a value and not having to 
look at the 
direction of movement of the 
function.
 
Clyde
 
 
 
{  Function Moondays returns the 
number of days since a new moon.  The values returned range between 0 
and 29.  (0 = new, and 15 is a full moon to +/- 2 day 
accuracy.)    Author: Gary Funck, <A 
href="mailto:gary@xxxxxxxxxxxx";>gary@xxxxxxxxxxxx, 7/15/97  No 
restrictions on use/copying. No warranties, expressed/implied.
 
  This code uses an approximation 
described in the "Astro FAQ";  summarized below:
 
  Subject: C.11  How do I 
calculate the phase of the moon?  Author: Bill Jefferys <<A 
href="mailto:bill@xxxxxxxxxxxxxxxxxxx";>bill@xxxxxxxxxxxxxxxxxxx>  
  John Horton Conway (the Princeton mathematician who is responsible 
for  "the Game of Life") wrote a book with Guy and Berlekamp, 
_Winning  Ways_, that describes in Volume 2 a number of useful 
calendrical  rules.  One of these is an easy "in your head" 
algorithm for  calculating the phase of the Moon, good to a day or 
better depending  on whether you use his refinements or not.  
  In the 20th century, calculate the remainder upon dividing 
the  last two digits of the year by 19; if greater than 9, 
subtract  19 from this to get a number between -9 and 9.   
  Multiply the result by 11 and reduce modulo 30 to obtain a  
number between -29 and +29.    Add the day of the month and 
the number of the month (except  for Jan and Feb use 3 and 4 for the 
month number instead of  1 and 2).    Subtract 
4.    Reduce modulo 30 to get a number between 0 and 29. This 
is  the age of the Moon.    Example: What was the 
phase of the Moon on D-Day (June 6,  1944)?    
Answer: 44/19=2 remainder 6.    6*11=66, reduce modulo 30 to 
get 6.    Add 6+6 to this and subtract 4: 6+6+6-4=14; the Moon 
was (nearly)  full. I understand that the planners of D-day did care 
about the phase  of the Moon, either because of illumination or because 
of tides. I  think that Don Olsen recently discussed this in _Sky and 
Telescope_  (within the past several years).    In 
the 21st century use -8.3 days instead of -4 for the last number.  
  Conway also gives refinements for the leap year cycle and 
also  for the slight variations in the lengths of months; what I 
have  given should be good to +/- a day or so.}inputs: 
dt(numericsimple);variables: x1(0), x2(0), x3(0), 
x4(0);    x1 = Mod(year(dt), 19);    if x1 
> 9 then x1 = x1 - 19;    x2 = Mod(x1 * 11, 
30);    x3 = month(dt);    if month(dt) 
< 3 then x3 = x3 + 2;    x4 = x2 + dayofmonth(dt) + x3 - 
4;    Moondays = Mod(x4, 30);
 
 
- - - - - - - - - - - - - - - - - - - - -  - - - - - - -Clyde 
Lee   
Chairman/CEO          (Home of 
SwingMachine)SYTECH 
Corporation          email: <A 
href="mailto:clydelee@xxxxxxxxxxxx";>clydelee@xxxxxxxxxxxx  7910 
Westglen, Suite 105       
Office:    (713) 783-9540Houston,  TX  
77063               
Fax:    (713) 783-1092Details 
at:                      
www.theswingmachine.com- - - - 
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<BLOCKQUOTE dir=ltr 
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  ----- Original Message ----- 
  <DIV 
  style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black">From: 
  <A title=catapult@xxxxxxxxxxxxxxxxxx 
  href="mailto:catapult@xxxxxxxxxxxxxxxxxx";>DH 
  To: <A title=realtraders@xxxxxxxxxxxxxxx 
  href="mailto:realtraders@xxxxxxxxxxxxxxx";>realtraders@xxxxxxxxxxxxxxx 
  
  Sent: Sunday, April 29, 2001 15:37
  Subject: Re: [RT] The moon cycle - how 
  strong?
  Here's a simple moon phase indicator for TS. A new moon is 
  zero and a full moon is 1.{******************Indicator: 
  dhMoon3DH, 2000******************}Var: Phase(0);Phase 
  = AbsValue(2 * (FracPortion(DateToJulian(Date)/29.53059 + .4137) 
  -.5));Plot1(Phase,"Phase");--   Dennis To 
  unsubscribe from this group, send an email 
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