Hi Tater ,
Once per orbit , that is, once a month.The Moon is at perigee once every orbit (29.5 days) Moon.It Its the biggest and brightest full also brings higher ocean tides ... If you have perfectly aligned , Earth Casts a shadow on the moon , and there's a total lunar eclipse ..
His friend ,
Once in an orbital period. Any orbiting body must pass through the perigee or periapsis on every orbit, or it is no longer orbiting, but escaping or falling.
You must mean how often is there a full moon at perigee.
"Perigean full moons occur in runs. As it happens, the one December 31, 2009 is not the absolute closest of all. The full moon the night of January 29-30, 2010 will be a tiny bit closer!
The moon will be about 1,400 miles closer before dawn on January 30th than it is tonight [Dec31st]". -(from a month ago on Yahoo
"The full moon cycle is a cycle of about 14 lunations over which full moons vary in apparent size and age (time since new moon). The sequence is
Full moon big - (perigee at full moon)
Full moon young - (perigee at first quarter)
Full moon small - (perigee at new moon)
Full moon old - (perigee at last quarter)