The Vernal Equinox is a Solar constant. Too bad the constructed calendar of mere mortals isn't as accurate.
Nope.
The total angular momentum of the earth moon system, which is spin angular momentum plus orbital angular momentum, is constant. (The Sun plays a small part as well, which will be ignored for this discussion.) Friction of the oceans caused by tides is causing the Earth to slow down a tiny bit each year. This is approximately two milliseconds per century, and amazingly this causes the moon to recede by about 4 centimeters per year. As the Earth slows down, the Moon must recede (this is an increase in orbital momentum) to keep the total angular momentum a constant. In other words as the spin angular momentum of the earth decreases, the lunar orbital angular momentum must increase. Here is an interesting side note: the velocity of the moon will slow down as the orbit increases.