Module: Horologium::Data::LeapSeconds

Defined in:
lib/horologium/data/leap_seconds.rb,
sig/horologium/data/leap_seconds.rbs

Overview

The leap seconds, TAI - UTC, from the iers gem. Scales::UTC reads this to convert between UTC and TAI, and it is the default source. A caller with its own leap second data, a frozen bulletin or an alternative feed, can put another source in its place through Configuration#leap_second_source, as long as it answers LeapSeconds.tai_utc_at.

The lookup is by day. TAI - UTC steps at 0h UTC, so a scale asks for the offset at the start of a day; before 1972 it drifts through the day too, so the scale also asks part way through one. iers reads either from the bundled table with no network access.

Constant Summary collapse

MJD_OFFSET =

This constant is part of a private API. You should avoid using this constant if possible, as it may be removed or be changed in the future.

The days between a Julian Date and a Modified Julian Date, less the half day that puts a Julian Day Number, which counts from noon, onto the midnight a Modified Julian Date counts from. Subtracting it from a Julian Day Number gives the integer Modified Julian Date of that day's 0h, the shape iers reads.

Returns:

  • (Integer) 
2_400_001

Class Method Summary collapse

Class Method Details

.expires_on ⇒ Date?

The date the leap second data stops vouching for itself, from the file's own header, or nil when it states none. A date past it might miss a leap second announced since the file was made, which is what marks a UTC reading there :extrapolated.

Returns:

  • (Date, nil) 


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# File 'lib/horologium/data/leap_seconds.rb', line 49

def expires_on
  IERS::LeapSecond.expires_on
end

.tai_utc_at(day_number) ⇒ Integer, Rational

TAI - UTC at a point in UTC, the number of seconds TAI is ahead of UTC. From 1972 it is a whole number of seconds, an Integer; between 1961 and 1972, when UTC drifted, it is a fraction of a second, a Rational. Either is exact. The point is a day by its Julian Day Number, or part way through one where a fraction is added.

Parameters:

  • day_number (Integer, Rational) —

    the Julian Day Number of the day, or a point through it

Returns:

  • (Integer, Rational) —

    TAI - UTC in seconds

Raises:

  • (IERS::OutOfRangeError) —

    before 1961, where TAI - UTC is not defined; Scales::UTC stops there before this is reached



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# File 'lib/horologium/data/leap_seconds.rb', line 39

def tai_utc_at(day_number)
  IERS::LeapSecond.at(mjd: day_number - MJD_OFFSET)
end