Earth Spun Slower Before Noah's Flood - A 360 Day Year Divided By 12 Lunar Months Of 30 days counted off Exactly One Solar AND Lunar Year.
Sun & Moon were in Sync - Solar & Lunar years BOTH totaled 360 days ... No Problem
When Earth's rotation sped up & a Solar Year became 365 1/4 days, the Solar & Lunar years no longer coincided.
There's now a 5 1/4 day discrepancy between Solar & Lunar years & attempting to measure years by Lunar months is thus Complicated & Imprecise.
See beginning @ 2:28:00 -
Which - According To The Theory - explains Why the Chinese (and virtually All ancient cultures/civilizations) relied on a Lunar Calendar in the Post-Flood World.
In response to: PHYSICAL MECHANISM:
It has been inconceivable to secularists, and even to most all creationists until recently, that in historical times the Earth's rotation could have sped up. However, Dr. Walt Brown's Hydroplate Theory presents just such a mechanism. The 46,000-mile globe-encircling crack known as the mid-oceanic ridge winds itself around the Earth like a seam on a baseball. That massive ridge is the scar remaining from the global flood's eruption of the fountains of the great deep. As the crust began to erode away, most severely in the Atlantic region, the mantle below rose precipitously, isostatically rebounding with the crust in the Pacific sinking into the Earth. Thus, much of the oceanic crust in the Atlantic is missing, and much of the crust in the Pacific is buried (see our video). As mass shifted through the Earth from the Pacific to the Atlantic, friction melted what became the molten outer core, seven moons worth of mass, doubling the density of that material. That tectonic activity is what destabilized the Earth. The deep melting is the ultimate cause of the unexpectedly deep earthquakes that confound many old-earth geologists (because after billions of years the deep earth would be far more stable than it actually is). That far more dense, melted material also shrunk the circumference of the Earth by about 180 miles. So by the law of the conservation of angular momentum, like a spinning figure skater pulling in her arms, the Earth's rotation sped up. This changed the year from a perfect 360, to our current difficult-to-calculate-with 365.2425 days. And the violent impacts that hit mostly on the moon's near side reduced its perfect 30-day orbit to today's 29.53-day lunar month.
In response to: Genesis 1: 14 - Young's Literal Translation
"And God saith, 'Let luminaries be in the expanse of the heavens, to make a separation between the day and the night, then they have been for signs, and for seasons, and for days and years,'"
Short Answer to the question posed in the OP - The Flood Did It! ...
online today!miclee Blog (348)
DUHH!
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Enjoy, Y'all!!
Get it, y'all ... GINGER! 
and enjoy - Well worth a watch ... 
