NAME

Astro::Montenbruck::Time::DeltaT - difference between UT and TDT.

VERSION

Version 0.01

DESCRIPTION

Delta-T indicates the difference between UT and TDT (Terrestrial Dynamic Time), which used to be called Ephemeris time in the last century. While UT is not a uniform time scale (it is occasionally adjusted, due to irregularities in the Earth's rotation), TDT is a uniform time scale which is needed as an argument for mathematical theories of celestial movements.

Formulae used by /delta_t subroutine, are based on NASA Technical Publication "Five Millennium Canon of Solar Eclipses: -1999 to +3000". They are valid for any time during the interval 2000 B.C. to 3000 A.D. See NASA Eclipse web site.

EXPORT

• "delta_t( $jd )"

SUBROUTINES

delta_t( $jd )

Returns approximate Delta-T in seconds for a given Julian Day. Delta-T = ET - UT

For a historical range from 1620 to recent years, we interpolate from a table of observed values. Outside that range we use formulae from Astronomical Algorithms by J.Meeus, second edition.

Arguments

• $jd — Standard Julian Date.

Returns

Delta-T in seconds