Re: Recurrence of a lunar phase


Michael wrote:
>
> The full moon falls of the 16th this month (Nov '05). In what year will
> it fall on this day of this month next? In other words, how often does
> a particular phase of the moon fall on a particular day of a given
> month?
>
It would fall on the same day of each month if we used a lunar
calendar.

However the word month was invented at the same time as the rest of
astrometry so the use of the term was originally given to the divisions
of the zodiac. In the early Roman era this was changed from a metric
division to an irregulat restoration of the 12 months.

However if they were regular 12 monthly intervals of 365.25* days, they
would occur with divisions of 29.5* days imposed on a roll over of
30.5* days.

But you have the odd month of February to contend with and the
September, April, June and November -as the saying goes, 30 days.

It takes something like 27.3* days for the moon to rotate around the
earth. If we were not in orbit around the sun that would be the length
of the month. Their dual relationship with the position around the sun
the time of the run of phases is extended to about 29/30 days.
However:

The days are shorter when we are nearest the sun as the earth and moon
are running through the orbit fastest then reducing the time to run
through the lunar phases.

At apogee (the point in the orbit of the moon or of an artificial
satellite most distant from the center of the earth) the earth and moon
are moving a little slower past the sun, so extending the time taken
to produce a full house.

In short, without the algorithm required to work it out, you had best
look at the remarkable effort produced by the much revered Dr Espenak:

http://sunearth.gsfc.nasa.gov/eclipse/phase/phasecat.html

It misses it it by a day in 2013 as it does again in 2024. For more
chances try:

http://sunearth.gsfc.nasa.gov/eclipse/phase/phasecat.html

(Nice one, Freddie)

.

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