# time/time-1.1.0¶

Represents an instance in time.

#### Description

A “time” is a single instant in time. It may explicitly specify the way time is represented (the “format”) and the “scale” which specifies the offset and scaling relation of the unit of time.

Specific emphasis is placed on supporting time scales (e.g. UTC, TAI, UT1, TDB) and time representations (e.g. JD, MJD, ISO 8601) that are used in astronomy and required to calculate, e.g., sidereal times and barycentric corrections.

Times may be represented as one of the following:

• an object, with explicit value, and optional format, scale and location.
• a string, in which case the format is guessed from across the unambiguous options (iso, byear, jyear, yday), and the scale is hardcoded to UTC.

In either case, a single time tag may be used to represent an n-dimensional array of times, using either an ndarray tag or inline as (possibly nested) YAML lists. If YAML lists, the same format must be used for all time values.

The precision of the numeric formats should only be assumed to be as good as an IEEE-754 double precision (float64) value. If higher-precision is required, the iso or yday format should be used.

### Schema Definitions ¶

This node must validate against any of the following:

• This type is an object with the following properties:
• value
 object Required
The value(s) of the time.

This node must validate against any of the following:

• format
 object
The format of the time.

If not provided, the the format should be guessed from the string from among the following unambiguous options: iso, byear, jyear and yday.

The supported formats are:

• iso: ISO 8601 compliant date-time format YYYY-MM- DDTHH:MM:SS.sss.... For example, 2000-01-01 00:00:00.000 is midnight on January 1, #. The T separating the date from the time section is optional.
• yday: Year, day-of-year and time as YYYY:DOY:HH:MM:SS.sss.... The day-of-year (DOY) goes from 001 to 365 (366 in leap years). For example, 2000:001:00:00:00.000 is midnight on January 1, 2000.
• byear: Besselian Epoch year, eg. B1950.0. The B is optional if the byear format is explicitly specified.
• jyear: Julian Epoch year, eg. J2000.0. The J is optional if the jyear format is explicitly specified.
• decimalyear: Time as a decimal year, with integer values corresponding to midnight of the first day of each year. For example 2000.5 corresponds to the ISO time 2000-07-02 00:00:00.
• jd: Julian Date time format. This represents the number of days since the beginning of the Julian Period. For example, 2451544.5 in jd is midnight on January 1, 2000.
• mjd: Modified Julian Date time format. This represents the number of days since midnight on November 17, 1858. For example, 51544.0 in MJD is midnight on January 1, 2000.
• gps: GPS time: seconds from 1980-01-06 00:00:00 UTC For example, 630720013.0 is midnight on January 1, 2000.
• unix: Unix time: seconds from 1970-01-01 00:00:00 UTC. For example, 946684800.0 in Unix time is midnight on January 1, 2000. [TODO: Astropy’s definition of UNIX time doesn’t match POSIX’s here. What should we do for the purposes of ASDF?]
This node has no type definition (unrestricted)
• scale
 object
The time scale (or time standard) is a specification for measuring time: either the rate at which time passes; or points in time; or both. See also [3] and [4].

These scales are defined in detail in SOFA Time Scale and Calendar Tools.

The supported time scales are:

• utc: Coordinated Universal Time (UTC). This is the default time scale, except for gps, unix.
• tai: International Atomic Time (TAI).
• tcb: Barycentric Coordinate Time (TCB).
• tcg: Geocentric Coordinate Time (TCG).
• tdb: Barycentric Dynamical Time (TDB).
• tt: Terrestrial Time (TT).
• ut1: Universal Time (UT1).
This node has no type definition (unrestricted)
• location
 object
Specifies the observer location for scales that are sensitive to observer location, currently only tdb. May be specified either with geocentric coordinates (X, Y, Z) with an optional unit or geodetic coordinates:

• long: longitude in degrees
• lat: in degrees
• h: optional height
This type is an object with the following properties:
• x
 ../unit/quantity-1.1.0 Required
• y
 ../unit/quantity-1.1.0 Required
• z
 ../unit/quantity-1.1.0 Required

### Examples ¶

Example ISO time:

!time/time-1.1.0 "2000-12-31T13:05:27.737"


Example year, day-of-year and time format time:

!time/time-1.1.0 "2001:003:04:05:06.789"


Example Besselian Epoch time:

!time/time-1.1.0 B2000.0


Example Besselian Epoch time, equivalent to above:

!time/time-1.1.0
value: 2000.0
format: byear


Example list of times:

!time/time-1.1.0
["2000-12-31T13:05:27.737", "2000-12-31T13:06:38.444"]


Example of an array of times:

!time/time-1.1.0
value: !core/ndarray-1.0.0
data: [2000, 2001]
datatype: float64
format: jyear


Example with a location:

!time/time-1.1.0
value: 2000.0
format: jyear
scale: tdb
location:
x: 6378100
y: 0
z: 0


### Internal Definitions ¶

• iso_time
 string
No length restriction
Must match the following pattern:
[0-9]{4}-(0[1-9])|(1[0-2])-(0[1-9])|([1-2][0-9])|(3[0-1])[T ]([0-1][0-9])|(2[0-4]):[0-5][0-9]:[0-5][0-9](.[0-9]+)?

• byear
 string
No length restriction
Must match the following pattern:
B[0-9]+(.[0-9]+)?

• jyear
 string
No length restriction
Must match the following pattern:
J[0-9]+(.[0-9]+)?

• yday
 string
No length restriction
Must match the following pattern:
[0-9]{4}:(00[1-9])|(0[1-9][0-9])|([1-2][0-9][0-9])|(3[0-5][0-9])|(36[0-5]):([0-1][0-9])|([0-1][0-9])|(2[0-4]):[0-5][0-9]:[0-5][0-9](.[0-9]+)?

• string_formats
 object

This node must validate against any of the following:

• array_of_strings
 array
No length restriction

Items in the array must be any of the following types:

• ### Original Schema ¶

%YAML 1.1
---
$schema: "http://stsci.edu/schemas/yaml-schema/draft-01" id: "http://stsci.edu/schemas/asdf/time/time-1.1.0" tag: "tag:stsci.edu:asdf/time/time-1.1.0" title: Represents an instance in time. description: | A "time" is a single instant in time. It may explicitly specify the way time is represented (the "format") and the "scale" which specifies the offset and scaling relation of the unit of time. Specific emphasis is placed on supporting time scales (e.g. UTC, TAI, UT1, TDB) and time representations (e.g. JD, MJD, ISO 8601) that are used in astronomy and required to calculate, e.g., sidereal times and barycentric corrections. Times may be represented as one of the following: - an object, with explicit value, and optional format, scale and location. - a string, in which case the format is guessed from across the unambiguous options (iso, byear, jyear, yday), and the scale is hardcoded to UTC. In either case, a single time tag may be used to represent an n-dimensional array of times, using either an ndarray tag or inline as (possibly nested) YAML lists. If YAML lists, the same format must be used for all time values. The precision of the numeric formats should only be assumed to be as good as an IEEE-754 double precision (float64) value. If higher-precision is required, the iso or yday format should be used. examples: - - Example ISO time - | !time/time-1.1.0 "2000-12-31T13:05:27.737" - - Example year, day-of-year and time format time - | !time/time-1.1.0 "2001:003:04:05:06.789" - - Example Besselian Epoch time - | !time/time-1.1.0 B2000.0 - - Example Besselian Epoch time, equivalent to above - | !time/time-1.1.0 value: 2000.0 format: byear - - Example list of times - | !time/time-1.1.0 ["2000-12-31T13:05:27.737", "2000-12-31T13:06:38.444"] - - Example of an array of times - | !time/time-1.1.0 value: !core/ndarray-1.0.0 data: [2000, 2001] datatype: float64 format: jyear - - Example with a location - | !time/time-1.1.0 value: 2000.0 format: jyear scale: tdb location: x: 6378100 y: 0 z: 0 definitions: iso_time: type: string pattern: "[0-9]{4}-(0[1-9])|(1[0-2])-(0[1-9])|([1-2][0-9])|(3[0-1])[T ]([0-1][0-9])|(2[0-4]):[0-5][0-9]:[0-5][0-9](.[0-9]+)?" byear: type: string pattern: "B[0-9]+(.[0-9]+)?" jyear: type: string pattern: "J[0-9]+(.[0-9]+)?" yday: type: string pattern: "[0-9]{4}:(00[1-9])|(0[1-9][0-9])|([1-2][0-9][0-9])|(3[0-5][0-9])|(36[0-5]):([0-1][0-9])|([0-1][0-9])|(2[0-4]):[0-5][0-9]:[0-5][0-9](.[0-9]+)?" string_formats: anyOf: -$ref: "#/definitions/iso_time"
- $ref: "#/definitions/byear" -$ref: "#/definitions/jyear"
- $ref: "#/definitions/yday" array_of_strings: type: array items: anyOf: -$ref: "#/definitions/array_of_strings"
- $ref: "#/definitions/string_formats" anyOf: -$ref: "#/definitions/string_formats"

- $ref: "#/definitions/array_of_strings" -$ref: "../core/ndarray-1.0.0#/anyOf/1"

- type: object
properties:
value:
description: |
The value(s) of the time.

anyOf:
- $ref: "#/definitions/string_formats" -$ref: "#/definitions/array_of_strings"
- $ref: "../core/ndarray-1.0.0" - type: number format: description: | The format of the time. If not provided, the the format should be guessed from the string from among the following unambiguous options: iso, byear, jyear and yday. The supported formats are: - iso: ISO 8601 compliant date-time format YYYY-MM-DDTHH:MM:SS.sss.... For example, 2000-01-01 00:00:00.000 is midnight on January 1, 2000. The T separating the date from the time section is optional. - yday: Year, day-of-year and time as YYYY:DOY:HH:MM:SS.sss.... The day-of-year (DOY) goes from 001 to 365 (366 in leap years). For example, 2000:001:00:00:00.000 is midnight on January 1, 2000. - byear: Besselian Epoch year, eg. B1950.0. The B is optional if the byear format is explicitly specified. - jyear: Julian Epoch year, eg. J2000.0. The J is optional if the jyear format is explicitly specified. - decimalyear: Time as a decimal year, with integer values corresponding to midnight of the first day of each year. For example 2000.5 corresponds to the ISO time 2000-07-02 00:00:00. - jd: Julian Date time format. This represents the number of days since the beginning of the Julian Period. For example, 2451544.5 in jd is midnight on January 1, 2000. - mjd: Modified Julian Date time format. This represents the number of days since midnight on November 17, 1858. For example, 51544.0 in MJD is midnight on January 1, 2000. - gps: GPS time: seconds from 1980-01-06 00:00:00 UTC For example, 630720013.0 is midnight on January 1, 2000. - unix: Unix time: seconds from 1970-01-01 00:00:00 UTC. For example, 946684800.0 in Unix time is midnight on January 1, 2000. [TODO: Astropy's definition of UNIX time doesn't match POSIX's here. What should we do for the purposes of ASDF?] enum: - iso - yday - byear - jyear - decimalyear - jd - mjd - gps - unix - cxcsec scale: description: | The time scale (or time standard) is a specification for measuring time: either the rate at which time passes; or points in time; or both. See also [3] and [4]. These scales are defined in detail in [SOFA Time Scale and Calendar Tools](http://www.iausofa.org/sofa_ts_c.pdf). The supported time scales are: - utc: Coordinated Universal Time (UTC). This is the default time scale, except for gps, unix. - tai: International Atomic Time (TAI). - tcb: Barycentric Coordinate Time (TCB). - tcg: Geocentric Coordinate Time (TCG). - tdb: Barycentric Dynamical Time (TDB). - tt: Terrestrial Time (TT). - ut1: Universal Time (UT1). enum: - utc - tai - tcb - tcg - tdb - tt - ut1 location: description: | Specifies the observer location for scales that are sensitive to observer location, currently only tdb. May be specified either with geocentric coordinates (X, Y, Z) with an optional unit or geodetic coordinates: - long: longitude in degrees - lat: in degrees - h: optional height type: object properties: x:$ref: "../unit/quantity-1.1.0"
y:
$ref: "../unit/quantity-1.1.0" z:$ref: "../unit/quantity-1.1.0"
required: [x, y, z]

required: [value]
...