[AstroPy] Time/IERS Question

[Josh Walawender]

Hi all,

I’m getting some behavior I don’t understand from astropy.time.  I’m trying to make a quick tool for printing out the current time in UT, MJD, and sidereal (LMST).  When I run it, I get an error on the step of calculating the sidereal time:

LST_string = now.sidereal_time('mean').to_string(sep=':',  precision=1)


Traceback (most recent call last):
  File "time_example.py", line 20, in <module>
    LST_string = now.sidereal_time('mean').to_string(sep=':',  precision=1)
  File "/Users/joshw/anaconda/lib/python2.7/site-packages/astropy/time/core.py", line 523, in sidereal_time
    gst = self._erfa_sidereal_time(available_models[model.upper()])
  File "/Users/joshw/anaconda/lib/python2.7/site-packages/astropy/time/core.py", line 539, in _erfa_sidereal_time
    for jd_part in ('jd1', 'jd2')]
  File "/Users/joshw/anaconda/lib/python2.7/site-packages/astropy/time/core.py", line 704, in __getattr__
    tm._set_scale(attr)
  File "/Users/joshw/anaconda/lib/python2.7/site-packages/astropy/time/core.py", line 372, in _set_scale
    args.append(get_dt(jd1, jd2))
  File "/Users/joshw/anaconda/lib/python2.7/site-packages/astropy/time/core.py", line 834, in _get_delta_ut1_utc
    delta = iers_table.ut1_utc(jd1, jd2)
  File "/Users/joshw/anaconda/lib/python2.7/site-packages/astropy/utils/iers/iers.py", line 234, in ut1_utc
    raise IndexError('(some) times are outside of range covered '
IndexError: (some) times are outside of range covered by IERS table.

When I go ahead and download the IERS table using the tools in astroplan:

from astroplan import download_IERS_A
download_IERS_A()

the code works.  But I need to do this download every time I run the code which is time consuming on code that I want to run many times.  Shouldn’t this be cached?

Any idea why the download is needed every time?

thanks!
Josh

P.S.  Entire code is pasted in below:



from datetime import datetime as dt
from astropy.time import Time
from astropy.coordinates import EarthLocation
import astropy.units as u

# from astroplan import download_IERS_A
# download_IERS_A()

utnow = dt.utcnow()
subaru = EarthLocation.from_geodetic(-155.476111111*u.degree,\
                                     19.8255555556*u.degree,\
                                     height=4139.0*u.meter)
now = Time(utnow, location=subaru)

UTC_string = utnow.strftime('%H:%M:%S.%f')
print(UTC_string)
MJD_string = '{:20.8f}'.format(now.mjd)
print(MJD_string)
LST_string = now.sidereal_time('mean').to_string(sep=':',  precision=1)
print(LST_string)

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