TimeUnixTai#
- class astropy.time.TimeUnixTai(val1, val2, scale, precision, in_subfmt, out_subfmt, from_jd=False)[source]#
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
andunix_tai
time is no longer an integer.Because of the fractional adjustments, to be very precise,
unix_tai
is the number of seconds since1970-01-01 00:00:00 TAI
or equivalently1969-12-31 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
andunix_tai
times increases linearly through the day by 1.0. See also the documentation for theTimeUnix
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 np.float64(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 np.float64(8.000082)
>>> # Initial offset of 10 seconds in 1972 >>> t = Time('1972-01-01', scale='utc') >>> t.unix_tai - t.unix np.float64(10.0)
Attributes Summary
Reference epoch time from which the time interval is measured.
Time scale.
Return time representation from internal jd1 and jd2.
Methods Summary
fill_value
(subfmt)Return a value corresponding to J2000 (2000-01-01 12:00:00) in this format.
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
- 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#
- name = 'unix_tai'#
- out_subfmt#
- precision#
- scale#
Time scale.
- subfmts = (('float', <class 'numpy.float64'>, None, <ufunc 'add'>), ('long', <class 'numpy.longdouble'>, <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
- classmethod fill_value(subfmt)#
Return a value corresponding to J2000 (2000-01-01 12:00:00) in this format.
This is used as a fill value for masked arrays to ensure that any ERFA operations on the masked array will not fail due to the masked 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.