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# Moon Day Table

7 replies to this topic

### #1 edosaurusrex

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Posted 27 January 2013 - 07:54 PM

The Subject should say "Unofficial Moon Day Table".

Yet another useless table that predicts when the Moon "Days" occur. A "Day" is defined by me as 360 degrees divided by 29.53 days or 12.191 degrees of true elongation from the Sun. Day 1 = 12.191, Day 2 = 24.382, etc. I thought there might be at least two people out there that may want to capture the Moon photographically as it appears each "Day" for an entire month. Because the "Days" may occur when the Moon is not available to the observer the idea was to have the entire year to get a month of pictures. The times in the table will show the Moon at the same phase and ignores the effect of libration. So even though you capture a phase month the Moon's features will jiggle depending on when the photos are taken. The 1st and 28th Days will be a REAL challenge and the 29th day can be ignored all together. If nothing else, the times in the table will illustrate the irregularity month to month for a given phase and day to day for the phase increment.

CORRECTION: I found a glitch in the program that had a problem going from near 360 degrees back to zero in elongation which yielded erroneous results for "Day 29" that nobody will see any way. Here are the corrected values.
JAN 11 0823
FEB 9 2358
MAR 11 0802
APR 9 2157
MAY 9 1049
JUN 8 0214
JUL 7 2148
AUG 6 0804
SEP 5 0127
OCT 4 1543
NOV 3 0101
DEC 2 1732

Hopefully this will have no effect on the table's uselessness.

The "trap" for the prediction calculated the day fraction as "a"={(y1-y3)+/-sqrt[(y3-y1)^2-8(y1-2*y2+y3)*(y2-y)]}/[2*(y1-2*y2+y3)], where y1,y2,y3 are the calculated table values and y is the target elongation value.

Imagine the whackiness that would occur if y1=345deg, y2=357deg, and y3=9deg. The predictor curve would be nothing close to the rather smooth day to day values.

The smaller absolute value of "a" (because of the +/- on the sqrt in the equation), if between -1 and 1 determines the day fraction for the prediction. The quadratic equation for the enlongation is 2*y = (y1-2*y2+y3)*a^2+(y3-y1)*a+2*y2 [this ONLY works if the table day interval is 1].

### #2 Scott in NC

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Posted 27 January 2013 - 09:49 PM

Thanks for sharing that! I've got it bookmarked for future reference.

### #3 RobDob

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Posted 28 January 2013 - 10:54 PM

I'm very interested in this. Thanks Ed!

Rob

### #4 edosaurusrex

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Posted 28 January 2013 - 11:06 PM

I knew there would be at least two. I'm happy now.

### #5 shrevestan

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Posted 28 January 2013 - 11:38 PM

Bookmarked! Thanks!

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Posted 29 January 2013 - 07:30 AM

Me too, thanks!

### #7 Tom and Beth

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Posted 29 January 2013 - 03:29 PM

Another

### #8 Photobud

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Posted 29 January 2013 - 05:14 PM

I saved it too. Guess it's not "another useless table".

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