Module: IERS::DeltaT

Defined in:
lib/iers/delta_t.rb

Defined Under Namespace

Classes: Entry

Class Method Summary collapse

Class Method Details

.at(input = nil, jd: nil, mjd: nil) ⇒ Entry

Returns DeltaT (TT − UT1) in seconds with source metadata.

Parameters:

  • input (Time, Date, DateTime, nil) (defaults to: nil)
  • jd (Float, nil) (defaults to: nil) —

    Julian Date

  • mjd (Float, nil) (defaults to: nil) —

    Modified Julian Date

Returns:

  • (Entry) —

    DeltaT (TT − UT1) in seconds with source metadata

Raises:



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# File 'lib/iers/delta_t.rb', line 61

def at(input = nil, jd: nil, mjd: nil)
  query_mjd = TimeScale.to_mjd(input, jd: jd, mjd: mjd)
  y = mjd_to_decimal_year(query_mjd)

  if y < EARLIEST_YEAR
    raise OutOfRangeError.new(
      "DeltaT is only available from #{EARLIEST_YEAR.to_i} onward",
      requested_mjd: query_mjd
    )
  end

  if query_mjd < PRE_1972_MJD
    Entry.new(
      delta_t: polynomial_delta_t(y),
      mjd: query_mjd,
      source: :estimated
    )
  else
    tai_utc = LeapSecond.at(mjd: query_mjd)
    ut1_utc = UT1.at(mjd: query_mjd).ut1_utc

    Entry.new(
      delta_t: tai_utc + TimeScale::TT_TAI - ut1_utc,
      mjd: query_mjd,
      source: :measured
    )
  end
end