Time#
- class astropy.time.Time(val, val2=None, format=None, scale=None, precision=None, in_subfmt=None, out_subfmt=None, location=None, copy=False)[source]#
Bases:
TimeBase
Represent and manipulate times and dates for astronomy.
A
Time
object is initialized with one or more times in theval
argument. The input times inval
must conform to the specifiedformat
and must correspond to the specified timescale
. 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(Time.FORMATS) ['jd', 'mjd', 'decimalyear', 'unix', 'unix_tai', 'cxcsec', 'gps', 'plot_date', 'stardate', 'datetime', 'ymdhms', 'iso', 'isot', 'yday', 'datetime64', 'fits', 'byear', 'jyear', 'byear_str', 'jyear_str']
See also: http://docs.astropy.org/en/stable/time/
- Parameters:
- valsequence,
ndarray
, number,str
,bytes
, orTime
object
Value(s) to initialize the time or times. Bytes are decoded as ascii.
- val2sequence,
ndarray
, or number; optional Value(s) to initialize the time or times. Only used for numerical input, to help preserve precision.
- format
str
, optional Format of input value(s), specifying how to interpret them (e.g., ISO, JD, or Unix time). By default, the same format will be used for output representation.
- scale
str
, optional Time scale of input value(s), must be one of the following: (‘tai’, ‘tcb’, ‘tcg’, ‘tdb’, ‘tt’, ‘ut1’, ‘utc’)
- precision
int
, optional Digits of precision in string representation of time
- in_subfmt
str
, optional Unix glob to select subformats for parsing input times
- out_subfmt
str
, optional Unix glob to select subformat for outputting times
- location
EarthLocation
ortuple
, optional If given as an tuple, it should be able to initialize an an EarthLocation instance, i.e., either contain 3 items with units of length for geocentric coordinates, or contain a longitude, latitude, and an optional height for geodetic coordinates. Can be a single location, or one for each input time. If not given, assumed to be the center of the Earth for time scale transformations to and from the solar-system barycenter.
- copybool, optional
Make a copy of the input values
- valsequence,
Attributes Summary
Dict of time formats
List of time scales
Return an instance with the data transposed.
Return the cache associated with this instance.
TDB - TT time scale offset
UT1 - UTC time scale offset
Get or set time format.
Unix wildcard pattern to select subformats for parsing string input times.
Container for meta information like name, description, format.
First of the two doubles that internally store time value(s) in JD.
Second of the two doubles that internally store time value(s) in JD.
The number of dimensions of the instance and underlying arrays.
Unix wildcard pattern to select subformats for outputting times.
Decimal precision when outputting seconds as floating point (int value between 0 and 9 inclusive).
Time scale.
The shape of the time instances.
The size of the object, as calculated from its shape.
Get an instance without the mask.
Time value(s) in current format.
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, kind])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.
earth_rotation_angle
([longitude])Calculate local Earth rotation angle.
filled
(fill_value)Get a copy of the underlying data, with masked values filled in.
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.isclose
(other[, atol])Returns a boolean or boolean array where two Time objects are element-wise equal within a time tolerance.
light_travel_time
(skycoord[, kind, ...])Light travel time correction to the barycentre or heliocentre.
max
([axis, out, keepdims])Maximum along a given axis.
mean
([axis, dtype, out, keepdims, where])Mean 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
([format, copy, cls])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, out, mode])Return a new instance formed from the elements at the given indices.
to_datetime
([timezone, leap_second_strict])Convert to (potentially timezone-aware)
datetime
object.Output a string representation of the Time or TimeDelta object.
to_value
(format[, subfmt])Get time values expressed in specified output format.
transpose
(*args, **kwargs)Return an instance with the data transposed.
Attributes Documentation
- FORMATS = {'byear': <class 'astropy.time.formats.TimeBesselianEpoch'>, 'byear_str': <class 'astropy.time.formats.TimeBesselianEpochString'>, 'cxcsec': <class 'astropy.time.formats.TimeCxcSec'>, 'datetime': <class 'astropy.time.formats.TimeDatetime'>, 'datetime64': <class 'astropy.time.formats.TimeDatetime64'>, 'decimalyear': <class 'astropy.time.formats.TimeDecimalYear'>, 'fits': <class 'astropy.time.formats.TimeFITS'>, 'gps': <class 'astropy.time.formats.TimeGPS'>, 'iso': <class 'astropy.time.formats.TimeISO'>, 'isot': <class 'astropy.time.formats.TimeISOT'>, 'jd': <class 'astropy.time.formats.TimeJD'>, 'jyear': <class 'astropy.time.formats.TimeJulianEpoch'>, 'jyear_str': <class 'astropy.time.formats.TimeJulianEpochString'>, 'mjd': <class 'astropy.time.formats.TimeMJD'>, 'plot_date': <class 'astropy.time.formats.TimePlotDate'>, 'stardate': <class 'astropy.time.formats.TimeStardate'>, 'unix': <class 'astropy.time.formats.TimeUnix'>, 'unix_tai': <class 'astropy.time.formats.TimeUnixTai'>, 'yday': <class 'astropy.time.formats.TimeYearDayTime'>, 'ymdhms': <class 'astropy.time.formats.TimeYMDHMS'>}#
Dict of time formats
- SCALES = ('tai', 'tcb', 'tcg', 'tdb', 'tt', 'ut1', 'utc', 'local')#
List of time 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#
TDB - TT time scale offset
- delta_ut1_utc#
UT1 - UTC time scale offset
- 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', 'unix_tai', 'cxcsec', 'gps', 'plot_date', 'stardate', 'datetime', 'ymdhms', '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#
Container for meta information like name, description, format. This is required when the object is used as a mixin column within a table, but can be used as a general way to store meta information.
- 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.
- location#
- 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:
ValueError
If the new shape has the wrong total number of elements.
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.
- unmasked#
Get an instance without the mask.
Note that while one gets a new instance, the underlying data will be shared.
See also
- value#
Time value(s) in current format.
- writeable#
Methods Documentation
- argmax(axis=None, out=None)#
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)#
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, kind='stable')#
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.- Parameters:
- Returns:
- indices
ndarray
An array of indices that sort the time array.
- indices
- copy(format=None)#
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.
- diagonal(*args, **kwargs)#
Return an instance with the specified diagonals.
Parameters are as for
diagonal()
. All internal data are views of the data of the original.
- earth_rotation_angle(longitude=None)[source]#
Calculate local Earth rotation angle.
- Parameters:
- longitude
Quantity
,EarthLocation
,str
, or None; optional The longitude on the Earth at which to compute the Earth rotation angle (taken from a location as needed). If
None
(default), taken from thelocation
attribute of the Time instance. If the special string ‘tio’, the result will be relative to the Terrestrial Intermediate Origin (TIO) (i.e., the output ofera00
).
- longitude
- Returns:
Longitude
Local Earth rotation angle with units of hourangle.
See also
Notes
The difference between apparent sidereal time and Earth rotation angle is the equation of the origins, which is the angle between the Celestial Intermediate Origin (CIO) and the equinox. Applying apparent sidereal time to the hour angle yields the true apparent Right Ascension with respect to the equinox, while applying the Earth rotation angle yields the intermediate (CIRS) Right Ascension with respect to the CIO.
The result includes the TIO locator (s’), which positions the Terrestrial Intermediate Origin on the equator of the Celestial Intermediate Pole (CIP) and is rigorously corrected for polar motion. (except when
longitude='tio'
).References
IAU 2006 NFA Glossary (currently located at: https://syrte.obspm.fr/iauWGnfa/NFA_Glossary.html)
- filled(fill_value)#
Get a copy of the underlying data, with masked values filled in.
- Parameters:
- fill_value
object
Value to replace masked values with. Note that if this value is masked
- fill_value
See also
- flatten(*args, **kwargs)#
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)[source]#
Find UT1 - UTC differences by interpolating in IERS Table.
- Parameters:
- iers_table
IERS
, optional Table containing UT1-UTC differences from IERS Bulletins A and/or B. Default:
earth_orientation_table
(which in turn defaults to the combined version provided byIERS_Auto
).- return_statusbool
Whether to return status values. If
False
(default), iers raisesIndexError
if any time is out of the range covered by the IERS table.
- iers_table
- Returns:
- ut1_utc
float
orfloat
array
UT1-UTC, interpolated in IERS Table
- status
int
orint
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
- ut1_utc
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]...)
- insert(obj, values, axis=0)#
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.- valuesarray_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.
- obj
- Returns:
- out
Time
subclass New time object with inserted value(s)
- out
- isclose(other, atol=None)#
Returns a boolean or boolean array where two Time objects are element-wise equal within a time tolerance.
This evaluates the expression below:
abs(self - other) <= atol
- light_travel_time(skycoord, kind='barycentric', location=None, ephemeris=None)[source]#
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
.
- skycoord
- 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.
- time_offset
- max(axis=None, out=None, keepdims=False)#
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.
- mean(axis=None, dtype=None, out=None, keepdims=False, *, where=True)[source]#
Mean along a given axis.
This is similar to
mean()
, 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.mean
; sinceTime
instances are immutable, it is not possible to have an actualout
to store the result in.Similarly, the
dtype
argument is also present for compatibility only; it has no meaning forTime
.- Parameters:
- axis
None
orint
ortuple
ofint
, optional Axis or axes along which the means are computed. The default is to compute the mean of the flattened array.
- dtype
None
- out
None
- keepdimsbool, optional
If this is set to True, the axes which are reduced are left in the result as dimensions with size one. With this option, the result will broadcast correctly against the input array.
- wherearray_like of bool, optional
Elements to include in the mean. See
reduce
for details.
- axis
- Returns:
- m
Time
A new Time instance containing the mean values
- m
- min(axis=None, out=None, keepdims=False)#
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()[source]#
Creates a new object corresponding to the instant in time this method is called.
Note
“Now” is determined using the
now
function, so its accuracy and precision is determined by that function. Generally that means it is set by the accuracy of your system clock. The timezone is set to UTC.
- ptp(axis=None, out=None, keepdims=False)#
Peak to peak (maximum - minimum) along a given axis.
This method is similar to the
numpy.ptp()
function, 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)#
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(format=None, copy=False, cls=None)#
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.
- reshape(*args, **kwargs)#
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 usingNDArrayShapeMethods
).
- sidereal_time(kind, longitude=None, model=None)[source]#
Calculate sidereal time.
- Parameters:
- kind
str
'mean'
or'apparent'
, i.e., accounting for precession only, or also for nutation.- longitude
Quantity
,EarthLocation
,str
, or None; optional The longitude on the Earth at which to compute the Earth rotation angle (taken from a location as needed). If
None
(default), taken from thelocation
attribute of the Time instance. If the special string ‘greenwich’ or ‘tio’, the result will be relative to longitude 0 for models before 2000, and relative to the Terrestrial Intermediate Origin (TIO) for later ones (i.e., the output of the relevant ERFA function that calculates greenwich sidereal time).- 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.
- kind
- Returns:
Longitude
Local sidereal time, with units of hourangle.
Notes
The difference between apparent sidereal time and Earth rotation angle is the equation of the origins, which is the angle between the Celestial Intermediate Origin (CIO) and the equinox. Applying apparent sidereal time to the hour angle yields the true apparent Right Ascension with respect to the equinox, while applying the Earth rotation angle yields the intermediate (CIRS) Right Ascension with respect to the CIO.
For the IAU precession models from 2000 onwards, the result includes the TIO locator (s’), which positions the Terrestrial Intermediate Origin on the equator of the Celestial Intermediate Pole (CIP) and is rigorously corrected for polar motion (except when
longitude='tio'
or'greenwich'
).References
IAU 2006 NFA Glossary (currently located at: https://syrte.obspm.fr/iauWGnfa/NFA_Glossary.html)
- sort(axis=-1)#
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.
- squeeze(*args, **kwargs)#
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)[source]#
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
str
Format definition of return string.
- format_spec
- Returns:
- formatted
str
ornumpy.array
String or numpy.array of strings formatted according to the given format string.
- formatted
- classmethod strptime(time_string, format_string, **kwargs)[source]#
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:
- Returns:
- swapaxes(*args, **kwargs)#
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, out=None, mode='raise')#
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_datetime(timezone=None, leap_second_strict='raise')[source]#
Convert to (potentially timezone-aware)
datetime
object.If
timezone
is notNone
, return a timezone-aware datetime object.Since the
datetime
class does not natively handle leap seconds, the behavior when converting a time within a leap second is controlled by theleap_second_strict
argument. For example:>>> from astropy.time import Time >>> t = Time("2015-06-30 23:59:60.500") >>> print(t.to_datetime(leap_second_strict='silent')) 2015-07-01 00:00:00.500000
- Parameters:
- Returns:
datetime
If
timezone
is notNone
, output will be timezone-aware.
- to_string()#
Output a string representation of the Time or TimeDelta object.
Similar to
str(self.value)
(which uses numpy array formatting) but array values are evaluated only for the items that actually are output. For large arrays this can be a substantial performance improvement.- Returns:
- out
str
String representation of the time values.
- out
- to_value(format, subfmt='*')#
Get time values expressed in specified output format.
This method allows representing the
Time
object in the desired outputformat
and optional sub-formatsubfmt
. Available built-in formats includejd
,mjd
,iso
, and so forth. Each format can have its own sub-formatsFor built-in numerical formats like
jd
orunix
,subfmt
can be one of ‘float’, ‘long’, ‘decimal’, ‘str’, or ‘bytes’. Here, ‘long’ usesnumpy.longdouble
for somewhat enhanced precision (with the enhancement depending on platform), and ‘decimal’decimal.Decimal
for full precision. For ‘str’ and ‘bytes’, the number of digits is also chosen such that time values are represented accurately.For built-in date-like string formats, one of ‘date_hms’, ‘date_hm’, or ‘date’ (or ‘longdate_hms’, etc., for 5-digit years in
TimeFITS
). For sub-formats including seconds, the number of digits used for the fractional seconds is as set byprecision
.- Parameters:
- format
str
The format in which one wants the time values. Default: the current format.
- subfmt
str
orNone
, optional Value or wildcard pattern to select the sub-format in which the values should be given. The default of ‘*’ picks the first available for a given format, i.e., ‘float’ or ‘date_hms’. If
None
, use the instance’sout_subfmt
.
- format
- transpose(*args, **kwargs)#
Return an instance with the data transposed.
Parameters are as for
transpose()
. All internal data are views of the data of the original.