Time scales

[AdamRJensen]

It would be nice to add a subsection on the different time scales:

• Universal Time Coordinated (UTC)
• Universal Time (UT)
• Terrestrial Time (TT)
• DeltaT

Some relevant literature:

• DeltaT polynomials: https://eclipse.gsfc.nasa.gov/SEcat5/deltatpoly.html
• Morrison, L. and Stephenson, F. R., "Historical Values of the Earth's Clock Error ΔT and the Calculation of Eclipses", J. Hist. Astron., Vol. 35 Part 3, August 2004, No. 120, pp 327-336 (2004).