CGRO Mission Epoch (gdt.missions.cgro.time)

The CGRO Mission time is typically expressed as the Truncated Julian Date (TJD), which has an epoch of May 24, 1968 00:00:00 UTC. We have defined a specialized epoch to work with Astropy Time objects so that the CGRO mission time can be easily converted to/from other formats and time scales.

To use this, we simply import and create an astropy Time object with a ‘cgro’ format:

>>> from gdt.missions.cgro.time import Time
>>> cgro_met = Time(9983.5, format='cgro')
>>> cgro_met
<Time object: scale='utc' format='cgro' value=9983.5>

Now, say we want to retrieve the GPS timestamp:

>>> cgro_met.gps
495892810.0

The Astropy Time object readily converts it for us. We can also do the reverse conversion:

>>> gps_time = Time(cgro_met.gps, format='gps')
>>> gps_time
<Time object: scale='tai' format='gps' value=495892810.0>

>>> gps_time.cgro
9983.5

And we should, of course, get back the CGRO mission time we started with. This enables you do do any time conversions already provided by Astropy, as well as time conversions between other missions within the GDT.

In addition to time conversions, all time formatting available in Astropy is also available here. For example, we can format the CGRO mission time in ISO format:

>>> cgro_met.iso
'1995-09-23 12:00:00.000'

Additionally, there are some time utilities available to convert date/time formats found within BATSE files into the CGRO mission time standard. BATSE data files often have time definitions that are formatted as two numbers: a float whose integer is the year and fractional part is the day of the year; and another float that represents the number of seconds from the start of the UTC day. We can convert this representation into a Time object by using the from_day_time function:

>>> from gdt.missions.cgro.time import from_day_time
>>> batse_time = from_day_time(1995.266, 43200.0)
>>> batse_time
<Time object: scale='utc' format='datetime' value=1995-09-23 12:00:00>
>>> batse_time.cgro
9983.5

And by using the to_day_time utility, we can convert a Time object into the BATSE format:

>>> from gdt.missions.cgro.time import to_day_time
>>> batse_day, batse_secs = to_day_time(batse_time)
>>> batse_day, batse_secs
(1995.266, 43200.0)

Reference/API

gdt.missions.cgro.time Module

Functions

from_day_time(yyyy_ddd, day_secs)	Create from day-of-year and seconds-of-day.
to_day_time(time_obj)	Convert an astropy time object to day-of-year and seconds-of-day BATSE format.

Classes

TimeCgroSec(val1, val2, scale, precision, ...)	Truncated Julian Date + fraction of a day.
Time(val[, val2, format, scale, precision, ...])	Represent and manipulate times and dates for astronomy.

Class Inheritance Diagram