TimeDelta¶
-
class
astropy.time.
TimeDelta
(val, val2=None, format=None, scale=None, copy=False)[source] [edit on github]¶ Bases:
astropy.time.Time
Represent the time difference between two times.
A TimeDelta object is initialized with one or more times in the
val
argument. The input times inval
must conform to the specifiedformat
. The optionalval2
time input should be supplied only for numeric input formats (e.g. JD) where very high precision (better than 64-bit precision) is required.The allowed values for
format
can be listed with:>>> list(TimeDelta.FORMATS) ['sec', 'jd', 'datetime']
Note that for time differences, the scale can be among three groups: geocentric (‘tai’, ‘tt’, ‘tcg’), barycentric (‘tcb’, ‘tdb’), and rotational (‘ut1’). Within each of these, the scales for time differences are the same. Conversion between geocentric and barycentric is possible, as there is only a scale factor change, but one cannot convert to or from ‘ut1’, as this requires knowledge of the actual times, not just their difference. For a similar reason, ‘utc’ is not a valid scale for a time difference: a UTC day is not always 86400 seconds.
See also:
- http://docs.astropy.org/en/stable/time/
- http://docs.astropy.org/en/stable/time/index.html#time-deltas
Parameters: - val : sequence, ndarray, number,
Quantity
orTimeDelta
object Value(s) to initialize the time difference(s). Any quantities will be converted appropriately (with care taken to avoid rounding errors for regular time units).
- val2 : sequence, ndarray, number, or
Quantity
; optional Additional values, as needed to preserve precision.
- format : str, optional
Format of input value(s)
- scale : str, optional
Time scale of input value(s), must be one of the following values: (‘tdb’, ‘tt’, ‘ut1’, ‘tcg’, ‘tcb’, ‘tai’). If not given (or
None
), the scale is arbitrary; when added or subtracted from aTime
instance, it will be used without conversion.- copy : bool, optional
Make a copy of the input values
Attributes Summary
FORMATS
Dict of time delta formats. SCALES
List of time delta scales. T
Return an instance with the data transposed. cache
Return the cache associated with this instance. delta_tdb_tt
delta_ut1_utc
Get ERFA DUT arg = UT1 - UTC. format
Get or set time format. in_subfmt
Unix wildcard pattern to select subformats for parsing string input times. info
isscalar
jd1
First of the two doubles that internally store time value(s) in JD. jd2
Second of the two doubles that internally store time value(s) in JD. mask
masked
ndim
The number of dimensions of the instance and underlying arrays. out_subfmt
Unix wildcard pattern to select subformats for outputting times. precision
Decimal precision when outputting seconds as floating point (int value between 0 and 9 inclusive). scale
Time scale shape
The shape of the time instances. size
The size of the object, as calculated from its shape. value
Time value(s) in current format writeable
Methods Summary
argmax
([axis, out])Return indices of the maximum values along the given axis. argmin
([axis, out])Return indices of the minimum values along the given axis. argsort
([axis])Returns the indices that would sort the time array. copy
([format])Return a fully independent copy the Time object, optionally changing the format. diagonal
(*args, **kwargs)Return an instance with the specified diagonals. flatten
(*args, **kwargs)Return a copy with the array collapsed into one dimension. get_delta_ut1_utc
([iers_table, return_status])Find UT1 - UTC differences by interpolating in IERS Table. insert
(obj, values[, axis])Insert values before the given indices in the column and return a new Time
orTimeDelta
object.light_travel_time
(skycoord[, kind, …])Light travel time correction to the barycentre or heliocentre. max
([axis, out, keepdims])Maximum along a given axis. min
([axis, out, keepdims])Minimum along a given axis. now
()Creates a new object corresponding to the instant in time this method is called. ptp
([axis, out, keepdims])Peak to peak (maximum - minimum) along a given axis. ravel
(*args, **kwargs)Return an instance with the array collapsed into one dimension. replicate
(*args, **kwargs)Return a replica of the Time object, optionally changing the format. reshape
(*args, **kwargs)Returns an instance containing the same data with a new shape. sidereal_time
(kind[, longitude, model])Calculate sidereal time. sort
([axis])Return a copy sorted along the specified axis. squeeze
(*args, **kwargs)Return an instance with single-dimensional shape entries removed strftime
(format_spec)Convert Time to a string or a numpy.array of strings according to a format specification. strptime
(time_string, format_string, **kwargs)Parse a string to a Time according to a format specification. swapaxes
(*args, **kwargs)Return an instance with the given axes interchanged. take
(indices[, axis, mode])Return a new instance formed from the elements at the given indices. to
(*args, **kwargs)to_datetime
()Convert to datetime.timedelta
object.transpose
(*args, **kwargs)Return an instance with the data transposed. Attributes Documentation
-
FORMATS
= {'datetime': <class 'astropy.time.formats.TimeDeltaDatetime'>, 'jd': <class 'astropy.time.formats.TimeDeltaJD'>, 'sec': <class 'astropy.time.formats.TimeDeltaSec'>}¶ Dict of time delta formats.
-
SCALES
= ('tai', 'tt', 'tcg', 'tcb', 'tdb', 'ut1', 'local')¶ List of time delta scales.
-
T
¶ Return an instance with the data transposed.
Parameters are as for
T
. All internal data are views of the data of the original.
-
cache
¶ Return the cache associated with this instance.
-
delta_tdb_tt
¶
-
delta_ut1_utc
¶ Get ERFA DUT arg = UT1 - UTC. This getter takes optional jd1 and jd2 args because it gets called that way when converting time scales. If delta_ut1_utc is not yet set, this will interpolate them from the the IERS table.
-
format
¶ Get or set time format.
The format defines the way times are represented when accessed via the
.value
attribute. By default it is the same as the format used for initializing theTime
instance, but it can be set to any other value that could be used for initialization. These can be listed with:>>> list(Time.FORMATS) ['jd', 'mjd', 'decimalyear', 'unix', 'cxcsec', 'gps', 'plot_date', 'datetime', 'iso', 'isot', 'yday', 'datetime64', 'fits', 'byear', 'jyear', 'byear_str', 'jyear_str']
-
in_subfmt
¶ Unix wildcard pattern to select subformats for parsing string input times.
-
info
¶
-
isscalar
¶
-
jd1
¶ First of the two doubles that internally store time value(s) in JD.
-
jd2
¶ Second of the two doubles that internally store time value(s) in JD.
-
mask
¶
-
masked
¶
-
ndim
¶ The number of dimensions of the instance and underlying arrays.
-
out_subfmt
¶ Unix wildcard pattern to select subformats for outputting times.
-
precision
¶ Decimal precision when outputting seconds as floating point (int value between 0 and 9 inclusive).
-
scale
¶ Time scale
-
shape
¶ The shape of the time instances.
Like
shape
, can be set to a new shape by assigning a tuple. Note that if different instances share some but not all underlying data, setting the shape of one instance can make the other instance unusable. Hence, it is strongly recommended to get new, reshaped instances with thereshape
method.Raises: - AttributeError
If the shape of the
jd1
,jd2
,location
,delta_ut1_utc
, ordelta_tdb_tt
attributes cannot be changed without the arrays being copied. For these cases, use theTime.reshape
method (which copies any arrays that cannot be reshaped in-place).
-
size
¶ The size of the object, as calculated from its shape.
-
value
¶ Time value(s) in current format
-
writeable
¶
Methods Documentation
-
argmax
(axis=None, out=None) [edit on github]¶ Return indices of the maximum values along the given axis.
This is similar to
argmax()
, but adapted to ensure that the full precision given by the two doublesjd1
andjd2
is used. Seeargmax()
for detailed documentation.
-
argmin
(axis=None, out=None) [edit on github]¶ Return indices of the minimum values along the given axis.
This is similar to
argmin()
, but adapted to ensure that the full precision given by the two doublesjd1
andjd2
is used. Seeargmin()
for detailed documentation.
-
argsort
(axis=-1) [edit on github]¶ Returns the indices that would sort the time array.
This is similar to
argsort()
, but adapted to ensure that the full precision given by the two doublesjd1
andjd2
is used, and that corresponding attributes are copied. Internally, it useslexsort()
, and hence no sort method can be chosen.
-
copy
(format=None) [edit on github]¶ Return a fully independent copy the Time object, optionally changing the format.
If
format
is supplied then the time format of the returned Time object will be set accordingly, otherwise it will be unchanged from the original.In this method a full copy of the internal time arrays will be made. The internal time arrays are normally not changeable by the user so in most cases the
replicate()
method should be used.Parameters: - format : str, optional
Time format of the copy.
Returns: - tm : Time object
Copy of this object
-
diagonal
(*args, **kwargs) [edit on github]¶ Return an instance with the specified diagonals.
Parameters are as for
diagonal()
. All internal data are views of the data of the original.
-
flatten
(*args, **kwargs) [edit on github]¶ Return a copy with the array collapsed into one dimension.
Parameters are as for
flatten()
.
-
get_delta_ut1_utc
(iers_table=None, return_status=False) [edit on github]¶ Find UT1 - UTC differences by interpolating in IERS Table.
Parameters: - iers_table :
astropy.utils.iers.IERS
table, optional Table containing UT1-UTC differences from IERS Bulletins A and/or B. If
None
, use default version (seeastropy.utils.iers
)- return_status : bool
Whether to return status values. If
False
(default), iers raisesIndexError
if any time is out of the range covered by the IERS table.
Returns: - ut1_utc : float or float array
UT1-UTC, interpolated in IERS Table
- status : int or int array
Status values (if
return_status=`True`
)::astropy.utils.iers.FROM_IERS_B
astropy.utils.iers.FROM_IERS_A
astropy.utils.iers.FROM_IERS_A_PREDICTION
astropy.utils.iers.TIME_BEFORE_IERS_RANGE
astropy.utils.iers.TIME_BEYOND_IERS_RANGE
Notes
In normal usage, UT1-UTC differences are calculated automatically on the first instance ut1 is needed.
Examples
To check in code whether any times are before the IERS table range:
>>> from astropy.utils.iers import TIME_BEFORE_IERS_RANGE >>> t = Time(['1961-01-01', '2000-01-01'], scale='utc') >>> delta, status = t.get_delta_ut1_utc(return_status=True) >>> status == TIME_BEFORE_IERS_RANGE array([ True, False]...)
- iers_table :
-
insert
(obj, values, axis=0) [edit on github]¶ Insert values before the given indices in the column and return a new
Time
orTimeDelta
object.The values to be inserted must conform to the rules for in-place setting of
Time
objects (seeGet and set values
in theTime
documentation).The API signature matches the
np.insert
API, but is more limited. The specification of insert indexobj
must be a single integer, and theaxis
must be0
for simple row insertion before the index.Parameters: - obj : int
Integer index before which
values
is inserted.- values : array_like
Value(s) to insert. If the type of
values
is different from that of quantity,values
is converted to the matching type.- axis : int, optional
Axis along which to insert
values
. Default is 0, which is the only allowed value and will insert a row.
Returns: - out :
Time
subclass New time object with inserted value(s)
-
light_travel_time
(skycoord, kind='barycentric', location=None, ephemeris=None) [edit on github]¶ Light travel time correction to the barycentre or heliocentre.
The frame transformations used to calculate the location of the solar system barycentre and the heliocentre rely on the erfa routine epv00, which is consistent with the JPL DE405 ephemeris to an accuracy of 11.2 km, corresponding to a light travel time of 4 microseconds.
The routine assumes the source(s) are at large distance, i.e., neglects finite-distance effects.
Parameters: - skycoord :
SkyCoord
The sky location to calculate the correction for.
- kind : str, optional
'barycentric'
(default) or'heliocentric'
- location :
EarthLocation
, optional The location of the observatory to calculate the correction for. If no location is given, the
location
attribute of the Time object is used- ephemeris : str, optional
Solar system ephemeris to use (e.g., ‘builtin’, ‘jpl’). By default, use the one set with
astropy.coordinates.solar_system_ephemeris.set
. For more information, seesolar_system_ephemeris
.
Returns: - time_offset :
TimeDelta
The time offset between the barycentre or Heliocentre and Earth, in TDB seconds. Should be added to the original time to get the time in the Solar system barycentre or the Heliocentre. Also, the time conversion to BJD will then include the relativistic correction as well.
- skycoord :
-
max
(axis=None, out=None, keepdims=False) [edit on github]¶ Maximum along a given axis.
This is similar to
max()
, but adapted to ensure that the full precision given by the two doublesjd1
andjd2
is used, and that corresponding attributes are copied.Note that the
out
argument is present only for compatibility withnp.max
; sinceTime
instances are immutable, it is not possible to have an actualout
to store the result in.
-
min
(axis=None, out=None, keepdims=False) [edit on github]¶ Minimum along a given axis.
This is similar to
min()
, but adapted to ensure that the full precision given by the two doublesjd1
andjd2
is used, and that corresponding attributes are copied.Note that the
out
argument is present only for compatibility withnp.min
; sinceTime
instances are immutable, it is not possible to have an actualout
to store the result in.
-
classmethod
now
() [edit on github]¶ Creates a new object corresponding to the instant in time this method is called.
Note
“Now” is determined using the
utcnow
function, so its accuracy and precision is determined by that function. Generally that means it is set by the accuracy of your system clock.Returns:
-
ptp
(axis=None, out=None, keepdims=False) [edit on github]¶ Peak to peak (maximum - minimum) along a given axis.
This is similar to
ptp()
, but adapted to ensure that the full precision given by the two doublesjd1
andjd2
is used.Note that the
out
argument is present only for compatibility withptp
; sinceTime
instances are immutable, it is not possible to have an actualout
to store the result in.
-
ravel
(*args, **kwargs) [edit on github]¶ Return an instance with the array collapsed into one dimension.
Parameters are as for
ravel()
. Note that it is not always possible to unravel an array without copying the data. If you want an error to be raise if the data is copied, you should should assign shape(-1,)
to the shape attribute.
-
replicate
(*args, **kwargs)[source] [edit on github]¶ Return a replica of the Time object, optionally changing the format.
If
format
is supplied then the time format of the returned Time object will be set accordingly, otherwise it will be unchanged from the original.If
copy
is set toTrue
then a full copy of the internal time arrays will be made. By default the replica will use a reference to the original arrays when possible to save memory. The internal time arrays are normally not changeable by the user so in most cases it should not be necessary to setcopy
toTrue
.The convenience method copy() is available in which
copy
isTrue
by default.Parameters: - format : str, optional
Time format of the replica.
- copy : bool, optional
Return a true copy instead of using references where possible.
Returns: - tm : Time object
Replica of this object
-
reshape
(*args, **kwargs) [edit on github]¶ Returns an instance containing the same data with a new shape.
Parameters are as for
reshape()
. Note that it is not always possible to change the shape of an array without copying the data (seereshape()
documentation). If you want an error to be raise if the data is copied, you should assign the new shape to the shape attribute (note: this may not be implemented for all classes usingShapedLikeNDArray
).
-
sidereal_time
(kind, longitude=None, model=None) [edit on github]¶ Calculate sidereal time.
Parameters: - kind : str
'mean'
or'apparent'
, i.e., accounting for precession only, or also for nutation.- longitude :
Quantity
,str
, orNone
; optional The longitude on the Earth at which to compute the sidereal time. Can be given as a
Quantity
with angular units (or anAngle
orLongitude
), or as a name of an observatory (currently, only'greenwich'
is supported, equivalent to 0 deg). IfNone
(default), thelon
attribute of the Time object is used.- model : str or
None
; optional Precession (and nutation) model to use. The available ones are: - apparent: [‘IAU1994’, ‘IAU2000A’, ‘IAU2000B’, ‘IAU2006A’] - mean: [‘IAU1982’, ‘IAU2000’, ‘IAU2006’] If
None
(default), the last (most recent) one from the appropriate list above is used.
Returns: - sidereal time :
Longitude
Sidereal time as a quantity with units of hourangle
-
sort
(axis=-1) [edit on github]¶ Return a copy sorted along the specified axis.
This is similar to
sort()
, but internally uses indexing withlexsort()
to ensure that the full precision given by the two doublesjd1
andjd2
is kept, and that corresponding attributes are properly sorted and copied as well.Parameters: - axis : int or None
Axis to be sorted. If
None
, the flattened array is sorted. By default, sort over the last axis.
-
squeeze
(*args, **kwargs) [edit on github]¶ Return an instance with single-dimensional shape entries removed
Parameters are as for
squeeze()
. All internal data are views of the data of the original.
-
strftime
(format_spec) [edit on github]¶ Convert Time to a string or a numpy.array of strings according to a format specification. See
time.strftime
documentation for format specification.Parameters: - format_spec : string
Format definition of return string.
Returns: - formatted : string, numpy.array
String or numpy.array of strings formatted according to the given format string.
-
classmethod
strptime
(time_string, format_string, **kwargs) [edit on github]¶ Parse a string to a Time according to a format specification. See
time.strptime
documentation for format specification.>>> Time.strptime('2012-Jun-30 23:59:60', '%Y-%b-%d %H:%M:%S') <Time object: scale='utc' format='isot' value=2012-06-30T23:59:60.000>
Parameters: - time_string : string, sequence, ndarray
Objects containing time data of type string
- format_string : string
String specifying format of time_string.
- kwargs : dict
Any keyword arguments for
Time
. If theformat
keyword argument is present, this will be used as the Time format.
Returns:
-
swapaxes
(*args, **kwargs) [edit on github]¶ Return an instance with the given axes interchanged.
Parameters are as for
swapaxes()
:axis1, axis2
. All internal data are views of the data of the original.
-
take
(indices, axis=None, mode='raise') [edit on github]¶ Return a new instance formed from the elements at the given indices.
Parameters are as for
take()
, except that, obviously, no output array can be given.
-
to
(*args, **kwargs)[source] [edit on github]¶
-
to_datetime
()[source] [edit on github]¶ Convert to
datetime.timedelta
object.
-
transpose
(*args, **kwargs) [edit on github]¶ Return an instance with the data transposed.
Parameters are as for
transpose()
. All internal data are views of the data of the original.