Converting between Different Time Representations#

In Accessing Times, we saw how to access the time columns/attributes of the TimeSeries and BinnedTimeSeries classes. Here we look in more detail at how to manipulate the resulting times.

Converting Times#

Since the time column in time series is always a Time object, it is possible to use the usual attributes on Time to convert the time to different formats or scales.


To get the times as modified Julian Dates from a minimal time series:

>>> from astropy import units as u
>>> from astropy.timeseries import TimeSeries
>>> ts = TimeSeries(time_start='2016-03-22T12:30:31', time_delta=3 * u.s,
...                 data={'flux': [1., 3., 4., 2., 4.]})
>>> ts.time.mjd  
array([57469.52119213, 57469.52122685, 57469.52126157, 57469.5212963 ,

Or to convert the times to the Temps Atomique International (TAI) scale:

>>> ts.time.tai
<Time object: scale='tai' format='isot' value=['2016-03-22T12:31:07.000' '2016-03-22T12:31:10.000'
 '2016-03-22T12:31:13.000' '2016-03-22T12:31:16.000'

To find the current time scale of the data, you can do:

>>> ts.time.scale

See Time and Dates (astropy.time) for more documentation on how to access and convert times.

Formatting Times#

Since the various time columns are Time objects, the default format and scale to use for the display of the time series can be changed using the format and scale attributes.


To change the display of the time series:

>>> ts.time.format = 'isot'
>>> ts
<TimeSeries length=5>
          time            flux
          Time          float64
----------------------- -------
2016-03-22T12:30:31.000     1.0
2016-03-22T12:30:34.000     3.0
2016-03-22T12:30:37.000     4.0
2016-03-22T12:30:40.000     2.0
2016-03-22T12:30:43.000     4.0
>>> ts.time.format = 'unix'
>>> ts  
<TimeSeries length=5>
    time       flux
    Time     float64
------------ -------
1458649831.0     1.0
1458649834.0     3.0
1458649837.0     4.0
1458649840.0     2.0
1458649843.0     4.0

Times Relative to Other Times#

In some cases, it can be useful to use relative rather than absolute times. This can be done by using the TimeDelta class instead of the Time class, for example, by subtracting a reference time from an existing Time object.


To use a relative rather than an absolute time:

>>> ts_rel = TimeSeries(time=ts.time - ts.time[0])
>>> ts_rel  
<TimeSeries length=5>

The TimeDelta values can be converted to a different time unit (e.g., second) using:

<Quantity [ 0.,  3.,  6.,  9., 12.] s>