Daniel R. Tobias replies to Poul-Henning Kamp:
Has anybody calculated how much energy is required to change
the Earths rotation fast enough to make this rule relevant ?
Superman could do it. Or perhaps he could nudge the Earth's rotation
just enough to make the length of a mean solar day exactly equal
86,400 SI seconds.
Only briefly. Consider the LOD plots from http://www.ucolick.org/
~sla/leapsecs/dutc.html. The Earth wobbles like a top, varying its
speed even if tidal slowing is ignored.
Actually, rather than being merely a troublemaker, the Moon serves to
stabilize the Earth's orientation. The "Rare Earth Hypothesis" makes
a strong case that a large Moon and other unlikely processes such as
continental drift are required for multicellular life to evolve, in
addition to the more familiar issues of a high system "metal" content
and a stable planetary orbit at a distance permitting liquid water.
Without the Moon, the Earth could nod through large angles, lying on
its side or perhaps even rotating retrograde every few million
years. Try making sense of timekeeping under such circumstances.
Rob Seaman
NOAO
