time_data.c File Reference

Look-up tables for ae_delta_t() and ae_dut1(). More...

Variables
short	ae_delta_t_tab []
	A table of delta_T = Ephemeris Time - Universal Time over many years. More...
const int	ae_delta_t_start_year = 1620
	The first year of delta T tabulation.
const int	ae_delta_t_end_year = 2024
	The final year of delta T tabulation.
short	ae_dut1_tab []
	A table of DUT1, the difference between UT1 and UTC. More...
const double	ae_dut1_first_mjd = 41684
	The Modified Julian Date of the first entry in ae_dut1_tab[].
const double	ae_dut1_last_mjd = 57606
	The Modified Julian Date of the last entry in ae_dut1_tab[].
const double	ae_dut1_predict_offset = 0.2645
	Offset for predicting DUT1 past the end of ae_dut1_tab[].
const double	ae_dut1_predict_scale = 0.00104
	Scale for predicting DUT1 past the end of ae_dut1_tab[].
const double	ae_dut1_predict_mjd = 57241
	Reference MJD for predicting DUT1 past the end of ae_dut1_tab[].

Detailed Description

Look-up tables for ae_delta_t() and ae_dut1().

This file was generated by parse_iers on Mar 14 2014 at 01:39:00.

Variable Documentation

short ae_delta_t_tab[]

A table of delta_T = Ephemeris Time - Universal Time over many years.

There is one value for each year, starting at #ae_delta_t_start_yearand ending at ae_delta_t_end_year.

The tabulated range is 1620.0 onwards. The values from 1620 to 1973 were taken from The Astronomical Almanac, page K8. The values from 2004 onwards (including future projections) are taken from http://maia.usno.navy.mil. Bessel's interpolation formula is implemented to obtain fourth order interpolated values at intermediate times.

Updated deltaT predictions can be obtained from this network archive:

• http://maia.usno.navy.mil

N.B.: Stephenson and Morrison's table starts at the year 1630. The Chapronts' table does not agree with the Almanac prior to 1630. The actual accuracy decreases rapidly prior to 1780.

Referenced by ae_delta_t().

short ae_dut1_tab[]

A table of DUT1, the difference between UT1 and UTC.

The entries are in tenths of milliseconds, beginning at the Modified Julian Date given by ae_dut1_first_mjd and incrementing every day thereafter. This format was chosen to minimise the amount of disc space used since short integers can be employed.

The last year of the table consists of forecasted values.

These data were taken from past IERS Bulletin A tables. Values can be found online at http://maia.usno.navy.mil/search/search.html; the file finals.all compiles all values since 1973.

Referenced by ae_dut1().