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- TimeUnixTai

# TimeUnixTai

class astropy.time.TimeUnixTai(val1, val2, scale, precision, in_subfmt, out_subfmt, from_jd=False)

  Bases: `TimeUnix`

  Unix time (TAI): SI seconds elapsed since 1970-01-01 00:00:00 TAI (see caveats).

  This will generally differ from standard (UTC) Unix time by the cumulative integral number of leap seconds introduced into UTC since 1972-01-01 UTC plus the initial offset of 10 seconds at that date.

  This convention matches the definition of linux CLOCK_TAI (https://www.cl.cam.ac.uk/~mgk25/posix-clocks.html), and the Precision Time Protocol (https://en.wikipedia.org/wiki/Precision_Time_Protocol), which is also used by the White Rabbit protocol in High Energy Physics: https://white-rabbit.web.cern.ch.

  Caveats:

  - Before 1972, fractional adjustments to UTC were made, so the difference between `unix` and `unix_tai` time is no longer an integer.

  - Because of the fractional adjustments, to be very precise, `unix_tai` is the number of seconds since `1970-01-01 00:00:00 TAI` or equivalently `1969-12-31 23:59:51.999918 UTC`. The difference between TAI and UTC at that epoch was 8.000082 sec.

  - On the day of a positive leap second the difference between `unix` and `unix_tai` times increases linearly through the day by 1.0. See also the documentation for the `TimeUnix` class.

  - Negative leap seconds are possible, though none have been needed to date.

  Examples

      >>> # get the current offset between TAI and UTC
      >>> from astropy.time import Time
      >>> t = Time('2020-01-01', scale='utc')
      >>> t.unix_tai - t.unix
      37.0

      >>> # Before 1972, the offset between TAI and UTC was not integer
      >>> t = Time('1970-01-01', scale='utc')
      >>> t.unix_tai - t.unix
      8.000082

      >>> # Initial offset of 10 seconds in 1972
      >>> t = Time('1972-01-01', scale='utc')
      >>> t.unix_tai - t.unix
      10.0

  Attributes Summary

  `cache` | Return the cache associated with this instance.
  `epoch` | Reference epoch time from which the time interval is measured
  `epoch_format` |
  `epoch_scale` |
  `epoch_val` |
  `epoch_val2` |
  `in_subfmt` |
  `jd1` |
  `jd2` |
  `jd2_filled` |
  `mask` |
  `masked` |
  `name` |
  `out_subfmt` |
  `precision` |
  `scale` | Time scale
  `subfmts` |
  `unit` |
  `value` | Return time representation from internal jd1 and jd2.

  Methods Summary

  `mask_if_needed`(value) |
  `set_jds`(val1, val2) | Initialize the internal jd1 and jd2 attributes given val1 and val2.
  `to_value`([parent]) | Return time representation from internal jd1 and jd2.

  Attributes Documentation

  cache

    Return the cache associated with this instance.

  epoch

    Reference epoch time from which the time interval is measured

  epoch_format = 'iso'
  epoch_scale = 'tai'
  epoch_val = '1970-01-01 00:00:00'
  epoch_val2 = None
  in_subfmt
  jd1
  jd2
  jd2_filled
  mask
  masked
  name = 'unix_tai'
  out_subfmt
  precision
  scale

    Time scale

  subfmts = (('float', <class 'numpy.float64'>, None, <ufunc 'add'>), ('long', <class 'numpy.float128'>, <function longdouble_to_twoval>, <function twoval_to_longdouble>), ('decimal', <class 'numpy.object_'>, <numpy.vectorize object>, <numpy.vectorize object>), ('str', <class 'numpy.str_'>, <numpy.vectorize object>, <numpy.vectorize object>), ('bytes', <class 'numpy.bytes_'>, <numpy.vectorize object>, <numpy.vectorize object>))
  unit = 1.1574074074074073e-05
  value

  Methods Documentation

  mask_if_needed(value)
  set_jds(val1, val2)

    Initialize the internal jd1 and jd2 attributes given val1 and val2. For an TimeFromEpoch subclass like TimeUnix these will be floats giving the effective seconds since an epoch time (e.g. 1970-01-01 00:00:00).

  to_value(parent=None, **kwargs)

    Return time representation from internal jd1 and jd2. Subclasses that require `parent` or to adjust the jds should override this method.