31. Dating

The sources of error in historical dating are legion, but seldom is the date of a lunar eclipse in doubt. Nearly 2000 years ago Ptolemy was confident he could compute eclipse dates many centuries in the future (and the past.) However, determining the start of ancient eclipses, their duration and other characteristics presents a complex of issues not yet resolved.

One difficulty stems from the non-Newtonian forces acting in the solar system. Newton's equations cannot account for the effect of ocean tides on astronomical observations. The formulas specify that tides impede the rotation of the earth, but only experimental evidence can quantify the slowing down.