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SuperNOVAS: src/timescale.c File Reference

Date

Created on Jun 24, 2024

Since

1.1

A set of SuperNOVAS routines to make handling of astronomical timescales and conversions among them easier.

See also

frames.c

Returns the TT - UT1 time difference given the leap seconds and the actual UT1 - UTC time difference as measured and published by IERS.

NOTES:

1. The current UT1 - UTC time difference, and polar offsets, historical data and near-term projections are published in the <a href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html>IERS Bulletins

Parameters

leap_seconds [s] Leap seconds at the time of observations dut1 [s] UT1 - UTC time difference [-0.5:0.5]

Returns

[s] The TT - UT1 time difference that is suitable for used with all calls in this library that require a ut1_to_tt argument.

See also

get_utc_to_tt()

place()

cel_pole()

Since

1.0

Author

Attila Kovacs

References get_utc_to_tt().

Returns the difference between Terrestrial Time (TT) and Universal Coordinated Time (UTC)

Parameters

leap_seconds [s] The current leap seconds (see IERS Bulletins)

Returns

[s] The TT - UTC time difference

See also

get_ut1_to_tt()

julian_date()

Since

1.0

Author

Attila Kovacs

References NOVAS_TAI_TO_TT.

Returns a Julian date (in non-specific timescale) corresponding the specified input string date/time. E.g. for "2025-02-28T09:41:12.041+0200", with some flexibility on how the date is represented as long as it's YMD date followed by HMS time. For other date formats (MDY or DMY) you can use novas_parse_date_format() instead.

Parameters

date The date specification, possibly including time and timezone, in a standard format. See novas_parse_date() on more information on acceptable date/time formats.

Returns

[day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since

1.3

Author

Attila Kovacs

See also

novas_date_scale()

novas_parse_date()

novas_parse_date_format()

novas_iso_timestamp()

References novas_parse_date().

Returns a Julian date and the timescale corresponding the specified input string date/time and timescale marker. E.g. for "2025-02-28T09:41:12.041+0200 TAI", with some flexibility on how the date is represented as long as it's YMD date followed by HMS time. For other date formats (MDY or DMY) you can use novas_parse_date_format() instead.

Parameters

date The date specification, possibly including time and timezone, in a standard format. See novas_parse_date() on more information on acceptable date/time formats. [out] scale The timescale constant, or else -1 if the string could not be parsed into a date and timescale. If the string is a bare timestamp without an hint of a timescale marker, then NOVAS_UTC will be assumed.

Returns

[day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since

1.3

Author

Attila Kovacs

See also

novas_date()

novas_timestamp()

References novas_parse_date(), and novas_parse_timescale().

Returns the Barycentric Coordinate Time (TCB) based time difference (t1 - t2) in days between two astronomical time specifications. TCB progresses slightly faster than time on Earth, at a rate about 1.6&times10^-8 higher, due to the lack of gravitational time dilation by the Earth or Sun.

Parameters

t1 First time t2 Second time

Returns

[s] Precise TCB time difference (t1-t2), or NAN if one of the inputs was NULL (errno will be set to EINVAL)

See also

novas_diff_tcg()

novas_diff_time()

Since

1.1

Author

Attila Kovacs

References novas_diff_time().

Returns the Geocentric Coordinate Time (TCG) based time difference (t1 - t2) in days between two astronomical time specifications. TCG progresses slightly faster than time on Earth, at a rate about 7&times10^-10 higher, due to the lack of gravitational time dilation by Earth. TCG is an appropriate time measure for a spacecraft that is in the proximity of the orbit of Earth, but far enough from Earth such that the relativistic effects of Earth's gravity can be ignored.

Parameters

t1 First time t2 Second time

Returns

[s] Precise TCG time difference (t1-t2), or NAN if one of the inputs was NULL (errno will be set to EINVAL)

See also

novas_diff_tcb()

novas_diff_time()

Since

1.1

Author

Attila Kovacs

References novas_diff_time().

Returns the fractional Julian date of an astronomical time in the specified timescale, as an integer and fractional part. The two-component split of the time allows for absolute precisions at the picosecond level, as opposed to novas_set_time(), whose precision is limited to a few microseconds typically.

The accuracy of Barycentric Time measures (TDB and TCB) relative to other time measures is limited by the precision of the tbd2tt() implemenation, to around 10 μs.

REFERENCES:

1. IAU 1991, RECOMMENDATION III. XXIst General Assembly of the International Astronomical Union. Retrieved 6 June 2019.
2. IAU 2006 resolution 3, see Recommendation and footnotes, note 3.
3. Fairhead, L. & Bretagnon, P. (1990) Astron. & Astrophys. 229, 240.
4. Kaplan, G. (2005), US Naval Observatory Circular 179.
5. https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/time.html
6. https://gssc.esa.int/navipedia/index.php/Transformations_between_Time_Systems

Parameters

time Pointer to the astronomical time specification data structure. timescale The astronomical time scale in which the returned Julian Date is to be provided [out] ijd [day] The integer part of the Julian date in the requested timescale. It may be NULL if not required.

Returns

[day] The fractional part of the Julian date in the requested timescale or NAN is the time argument is NULL (ijd will be set to -1 also).

See also

novas_set_split_time()

novas_get_time()

Since

1.1

Author

Attila Kovacs

References NOVAS_GPS, NOVAS_TAI, NOVAS_TCB, NOVAS_TCG, NOVAS_TDB, NOVAS_TT, NOVAS_UT1, and NOVAS_UTC.

Returns the fractional Julian date of an astronomical time in the specified timescale. The returned time is accurate to a few μs (microsecond) due to the inherent precision of the double-precision result. For higher precision applications you may use novas_get_split_time() instead, which has an inherent accuracy at the picosecond level.

Parameters

time Pointer to the astronomical time specification data structure. timescale The astronomical time scale in which the returned Julian Date is to be provided

Returns

[day] The Julian date in the requested timescale.

See also

novas_set_time()

novas_get_split_time()

Since

1.1

Author

Attila Kovacs

References novas_get_split_time().

Returns the UNIX time for an astronomical time instant.

Parameters

time Pointer to the astronomical time specification data structure. [out] nanos [ns] UTC sub-second component. It may be NULL if not required.

Returns

[s] The integer UNIX time, or -1 if the input time is NULL.

See also

novas_set_unix_time()

novas_get_time()

Since

1.1

Author

Attila Kovacs

References novas_get_split_time(), and NOVAS_UTC.

Prints a UTC-based ISO timestamp to millisecond precision to the specified string buffer. E.g.:

 2025-01-26T21:32:49.701Z

NOTES:

1. As per the ISO 8601 specification, the timestamp uses the Gregorian date, even for dates prior to the Gregorian calendar reform of 15 October 1582 (i.e. proleptic Gregorian dates).

2. B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

time Pointer to the astronomical time specification data structure. [out] dst Output string buffer. At least 25 bytes are required for a complete timestamp with termination. maxlen The maximum number of characters that can be printed into the output buffer, including the string termination. If the full ISO timestamp is longer than maxlen, then it will be truncated to fit in the allotted space, including a termination character.

Returns

the number of characters printed into the string buffer, not including the termination. As such it is at most maxlen - 1.

Since

1.3

Author

Attila Kovacs

See also

novas_timestamp()

novas_parse_iso_date()

References novas_get_split_time(), NOVAS_GREGORIAN_CALENDAR, and NOVAS_UTC.

Increments the astrometric time by a given amount.

Parameters

time Original time specification seconds [s] Seconds to add to the original [out] out New incremented time specification. It may be the same as the input.

Returns

0 if successful, or else -1 if either the input or the output is NULL (errno will be set to EINVAL).

See also

novas_set_time()

novas_diff_time()

Since

1.1

Author

Attila Kovacs

References novas_timespec::fjd_tt, and novas_timespec::ijd_tt.

Parses an astronomical date/time string into a Julian date specification.

The date must be YMD-type with full year, followed the month (numerical or name or 3-letter abbreviation), and the day. The components may be separated by dash -, underscore _, dot ., slash '/', or spaces/tabs, or any combination thereof. The date may be followed by a time specification in HMS format, separated from the date by the letter T or t, or spaces, comma ,, or semicolon ;, or underscore _ or a combination thereof. Finally, the time may be followed by the letter Z, or z (for UTC) or else {+/-}HH[:[MM]] time zone specification.

For example:

 2025-01-26
 2025 January 26
 2025_Jan_26
 2025-01-26T19:33:08Z
 2025.01.26T19:33:08
 2025 1 26 19h33m28.113
 2025/1/26 19:33:28+02
 2025-01-26T19:33:28-0600
 2025 Jan 26 19:33:28+05:30

are all valid dates that can be parsed.

NOTES:

1. This function assumes Gregorian dates after their introduction on 1582 October 15, and Julian/Roman dates before that, as was the convention of the time. I.e., the day before of the introduction of the Gregorian calendar reform is 1582 October 4. I.e., you should not use this function with ISO 8601 timestamps containing dates prior to 1582 October 15 (for such date you may use novas_parse_iso_date() instead).

2. B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

date The astronomical date specification, possibly including time and timezone, in a standard format. The date is assumed to be in the astronomical calendar of date, which differs from ISO 8601 timestamps for dates prior to the Gregorian calendar reform of 1582 October 15 (otherwise, the two are identical). [out] tail (optional) If not NULL it will be set to the next character in the string after the parsed time.

Returns

[day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since

1.3

Author

Attila Kovacs

See also

novas_parse_iso_date()

novas_parse_date_format()

novas_date()

novas_date_scale()

novas_timescale_for_string()

novas_iso_timestamp()

novas_timestamp()

References NOVAS_ASTRONOMICAL_CALENDAR, novas_parse_date_format(), and NOVAS_YMD.

Parses a calndar date/time string, expressed in the specified type of calendar, into a Julian day (JD). The date must be composed of a full year (e.g. 2025), a month (numerical or name or 3-letter abbreviation, e.g. "01", "1", "January", or "Jan"), and a day (e.g. "08" or "8"). The components may be separated by dash -, underscore _, dot ., slash '/', or spaces/tabs, or any combination thereof. The components will be parsed in the specified order.

The date may be followed by a time specification in HMS format, separated from the date by the letter T or t, or spaces, comma ,, or semicolon ; or underscore '_', or a combination thereof. Finally, the time may be followed by the letter Z, or z (for UTC) or else by a {+/-}HH[:[MM]] time zone specification.

For example, for format NOVAS_YMD, all of the following strings may specify the date:

 2025-01-26
 2025 January 26
 2025_Jan_26
 2025-01-26T19:33:08Z
 2025.01.26T19:33:08
 2025 1 26 19h33m28.113
 2025/1/26 19:33:28+02
 2025-01-26T19:33:28-0600
 2025 Jan 26 19:33:28+05:30

are all valid dates that can be parsed.

If your date format cannot be parsed with this function, you may parse it with your own function into year, month, day, and decimal hour-of-day components, and use julian_date() with those.

NOTES:

1. B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

calendar The type of calendar to use: NOVAS_ASTRONOMICAL_CALENDAR, NOVAS_GREGORIAN_CALENDAR, or NOVAS_ROMAN_CALENDAR. format Expected order of date components: NOVAS_YMD, NOVAS_DMY, or NOVAS_MDY. date The date specification, possibly including time and timezone, in the specified standard format. [out] tail (optional) If not NULL it will be set to the next character in the string after the parsed time.

Returns

[day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since

1.3

Author

Attila Kovacs

See also

novas_parse_date()

novas_parse_iso_date()

novas_timescale_for_string()

novas_iso_timestamp()

julian_date()

References novas_debug(), NOVAS_DEBUG_OFF, NOVAS_DMY, novas_get_debug_mode(), novas_jd_from_date(), NOVAS_MDY, novas_parse_hms(), and NOVAS_YMD.

Parses an ISO 8601 timestamp, converting it to a Julian day. It is equivalent to novas_parse_date() for dates after the Gregorian calendar reform of 1582. For earlier dates, ISO timestamps continue to assume the Gregorian calendar (i.e. proleptic Gregorian dates), whereas novas_parse_timestamp() will assume Roman/Julian dates, which were conventionally used before the calendar reform.

NOTES:

1. B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

date The ISO 8601 date specification, possibly including time and timezone, in a standard format. [out] tail (optional) If not NULL it will be set to the next character in the string after the parsed time.

Returns

[day] The Julian Day corresponding to the string date/time specification or NAN if the string is NULL or if it does not specify a date/time in the expected format.

Since

1.3

Author

Attila Kovacs

See also

novas_iso_timestamp()

novas_parse_date()

References NOVAS_GREGORIAN_CALENDAR, novas_parse_date_format(), and NOVAS_YMD.

Parses the timescale from a string containing a standard abbreviation (case insensitive), and returns the updated parse position after the timescale specification (if any). The following timescale values are recognised: "UTC", "UT", "UT0", "UT1", "GMT", "TAI", "GPS", "TT", "ET", "TCG", "TCB", "TDB".

Parameters

str String specifying an astronomical timescale. Leading white spaces will be skipped over. [out] tail (optional) If not NULL it will be set to the next character in the string after the parsed timescale specification.

Returns

The SuperNOVAS timescale constant (<=0), or else -1 if the string was NULL, empty, or could not be matched to a timescale value (errno will be set to EINVAL also).

Since

1.3

Author

Attila Kovacs

See also

novas_timescale_for_string()

novas_set_time()

novas_set_split_time()

novas_print_timescale()

References novas_timescale_for_string(), and NOVAS_UTC.

Prints the standard string representation of the timescale to the specified buffer. The string is terminated after. E.g. "UTC", or "TAI". It will print dates in the Gregorian calendar, which was introduced in was introduced on 15 October 1582 only. Thus the

Parameters

scale The timescale buf String in which to print. It should have at least 4-bytes of available storage.

Returns

the number of characters printed, not including termination, or else -1 if the timescale is invalid or the output buffer is NULL.

Since

1.3

Author

Attila Kovacs

See also

novas_timestamp()

novas_timescale_for_string()

References NOVAS_GPS, NOVAS_TAI, NOVAS_TCB, NOVAS_TCG, NOVAS_TDB, NOVAS_TT, NOVAS_UT1, and NOVAS_UTC.

Sets an astronomical time to the split Julian Date value, defined in the specified timescale. The split into the integer and fractional parts can be done in any convenient way. The highest precision is reached if the fractional part is ≤ 1 day. In that case, the time may be specified to picosecond accuracy, if needed.

The accuracy of Barycentric Time measures (TDB and TCB) relative to other time measures is limited by the precision of tbd2tt() implementation, to around 10 μs.

REFERENCES:

1. IAU 1991, RECOMMENDATION III. XXIst General Assembly of the International Astronomical Union. Retrieved 6 June 2019.
2. IAU 2006 resolution 3, see Recommendation and footnotes, note 3.
3. Fairhead, L. & Bretagnon, P. (1990) Astron. & Astrophys. 229, 240.
4. Kaplan, G. (2005), US Naval Observatory Circular 179.
5. https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/time.html
6. https://gssc.esa.int/navipedia/index.php/Transformations_between_Time_Systems

Parameters

timescale The astronomical time scale in which the Julian Date is given ijd [day] integer part of the Julian day in the specified timescale fjd [day] fractional part Julian day value in the specified timescale leap [s] Leap seconds, e.g. as published by IERS Bulletin C. dut1 [s] UT1-UTC time difference, e.g. as published in IERS Bulletin A. [out] time Pointer to the data structure that uniquely defines the astronomical time for all applications.

Returns

0 if successful, or else -1 if there was an error (errno will be set to indicate the type of error).

See also

novas_set_time()

novas_set_unix_time()

novas_get_split_time()

novas_timescale_for_string()

Since

1.1

Author

Attila Kovacs

References NOVAS_GPS, NOVAS_TAI, NOVAS_TCB, NOVAS_TCG, NOVAS_TDB, NOVAS_TT, NOVAS_UT1, NOVAS_UTC, and tt2tdb().

Sets an astronomical time to the fractional Julian Date value, defined in the specified timescale. The time set this way is accurate to a few μs (microseconds) due to the inherent precision of the double-precision argument. For higher precision applications you may use novas_set_split_time() instead, which has an inherent accuracy at the picosecond level.

Parameters

timescale The astronomical time scale in which the Julian Date is given jd [day] Julian day value in the specified timescale leap [s] Leap seconds, e.g. as published by IERS Bulletin C. dut1 [s] UT1-UTC time difference, e.g. as published in IERS Bulletin A. [out] time Pointer to the data structure that uniquely defines the astronomical time for all applications.

Returns

0 if successful, or else -1 if there was an error (errno will be set to indicate the type of error).

See also

novas_set_split_time()

novas_set_unix_time()

novas_get_time()

novas_timescale_for_string()

Since

1.1

Author

Attila Kovacs

References novas_set_split_time().

Sets an astronomical time to a UNIX time value. UNIX time is defined as UTC seconds measured since 0 UTC, 1 Jan 1970 (the start of the UNIX era). Specifying time this way supports precisions to the nanoseconds level by construct. Specifying UNIX time in split seconds and nanoseconds is a common way CLIB handles precision time, e.g. with struct timespec and functions like clock_gettime() (see time.h).

Parameters

unix_time [s] UNIX time (UTC) seconds nanos [ns] UTC sub-second component leap [s] Leap seconds, e.g. as published by IERS Bulletin C. dut1 [s] UT1-UTC time difference, e.g. as published in IERS Bulletin A. [out] time Pointer to the data structure that uniquely defines the astronomical time for all applications.

Returns

0 if successful, or else -1 if there was an error (errno will be set to indicate the type of error).

See also

novas_set_time()

novas_get_unix_time()

clock_gettime()

struct timespec

Since

1.1

Author

Attila Kovacs

References novas_set_split_time(), and NOVAS_UTC.

Returns the Local (apparent) Sidereal Time (LST/LaST) for a given astronomical time specification and observer location.

Parameters

time The astronomoical time specification. lon [deg] The geodetic longitude of the observer. accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1).

Returns

[h] The Local apparent Sidereal Time (LST / LaST) in the [0:24) hour range, or else NAN if there was an error (errno will indicate the type of error).

Since

1.4

Author

Attila Kovacs

See also

novas_frame_lst()

novas_set_time()

References novas_time_gst().

Returns the timescale constant for a string that denotes the timescale in with a standard abbreviation (case insensitive). The following values are recognised: "UTC", "UT", "UT0", "UT1", "GMT", "TAI", "GPS", "TT", "ET", "TCG", "TCB", "TDB".

Parameters

str String specifying an astronomical timescale

Returns

The SuperNOVAS timescale constant (<=0), or else -1 if the string was NULL, empty, or could not be matched to a timescale value (errno will be set to EINVAL also).

Since

1.3

Author

Attila Kovacs

See also

novas_parse_timescale()

novas_set_time()

novas_set_split_time()

novas_print_timescale()

References NOVAS_GPS, NOVAS_TAI, NOVAS_TCB, NOVAS_TCG, NOVAS_TDB, NOVAS_TT, NOVAS_UT1, and NOVAS_UTC.

Prints an astronomical timestamp to millisecond precision in the specified timescale to the specified string buffer. It differs from ISO 8601 timestamps for dates prior to the Gregorian calendar reform of 1582 October 15 (otherwise two are identical). E.g.:

 2025-01-26T21:32:49.701 TAI

NOTES:

1. The timestamp uses the astronomical date. That is Gregorian dates after the Gregorian calendar reform of 15 October 1582, and Julian/Roman dates prior to that. This is in contrast to ISO 8601 timestamps, which use Gregorian dates even for dates the precede the calendar reform that introduced them.

2. B.C. dates are indicated with years <=0 according to the astronomical and ISO 8601 convention, i.e., X B.C. as (1-X), so 45 B.C. as -44.

Parameters

time Pointer to the astronomical time specification data structure. scale The timescale to use. [out] dst Output string buffer. At least 28 bytes are required for a complete timestamp with termination. maxlen The maximum number of characters that can be printed into the output buffer, including the string termination. If the full ISO timestamp is longer than maxlen, then it will be truncated to fit in the allotted space, including a termination character.

Returns

the number of characters printed into the string buffer, not including the termination. As such it is at most maxlen - 1.

Since

1.3

Author

Attila Kovacs

See also

novas_iso_timestamp()

novas_parse_date()

References NOVAS_ASTRONOMICAL_CALENDAR, novas_get_split_time(), and novas_print_timescale().

Computes the Terrestrial Time (TT) based Julian date corresponding to a Barycentric Dynamical Time (TDB) Julian date, and retuns th TDB-TT time difference also. It has a maximum error of 10 μs between for dates 1600 and 2200.

This function is wrapped by tt2tdb(), which is typically a lot easier to use as it returns the time difference directly, which can then be used to convert time in both directions with greater ease. For exable to convert a TT-based date to a TDB-based date:

TDB = TT +

(TT) / 86400.0;

double tt2tdb(double jd_tt)

Definition timescale.c:178

is equivalent to:

double dt;

double TDB = TT + dt / 86400.0;

int tdb2tt(double jd_tdb, double *restrict jd_tt, double *restrict secdiff)

Definition timescale.c:133

NOTES:

1. This function caches the results of the last calculation in case it may be re-used at no extra computational cost for the next call.

REFERENCES:

1. Fairhead, L. & Bretagnon, P. (1990) Astron. & Astrophys. 229, 240.
2. Kaplan, G. (2005), US Naval Observatory Circular 179.

Parameters

jd_tdb [day] Barycentric Dynamic Time (TDB) based Julian date. [out] jd_tt [day] Terrestrial Time (TT) based Julian date. (It may be NULL if not required) [out] secdiff [s] Difference 'tdb_jd'-'tt_jd', in seconds. (It may be NULL if not required)

Returns

0

See also

tt2tdb()

References NOVAS_JD_J2000.

Returns the TDB - TT time difference in seconds for a given TT or TDB date, with a maximum error of 10 μs for dates between 1600 and 2200.

REFERENCES

1. Fairhead, L. & Bretagnon, P. (1990) Astron. & Astrophys. 229, 240.
2. Kaplan, G. (2005), US Naval Observatory Circular 179.
3. Moyer, T.D. (1981), Celestial mechanics, Volume 23, Issue 1, pp. 57-68<.li>

Parameters

jd_tt [day] Terrestrial Time (TT) based Julian date, but Barycentri Dynamical Time (TDB) can also be used here without any loss of precision on the result.

Returns

[s] TDB - TT time difference.

See also

tt2tdb_hp()

tt2tdb_fp()

tdb2tt()

Since

1.0

Author

Attila Kovacs

References tdb2tt().

Returns the TDB-TT time difference with flexible precision. This implementation uses the series expansion by Fairhead & Bretagnon 1990, terminating theterm at or below the specified limiting amplitude.

REFERENCES:

1. Fairhead, L., & Bretagnon, P. (1990) A&A, 229, 240

Parameters

jd_tt [day] Terrestrial Time (TT) based Julian date, but Barycentric Dynamical Time (TDB) limit [us] Amplitude of limiting term to include in series. 0 or negative values will include all terms, producing the same result as tt2tdb_hp().

Returns

[s] TDB - TT time difference.

Since

1.4

Author

Attila Kovacs

See also

tt2tdb_hp()

tt2tdb()

References NOVAS_JD_J2000.

Returns the TDB-TT time difference with flexible precision. This implementation uses the full series expansion by Fairhead & Bretagnon 1990, resulting in an accuracy below 100 ns.

REFERENCES:

1. Fairhead, L., & Bretagnon, P. (1990) A&A, 229, 240

Parameters

jd_tt [day] Terrestrial Time (TT) based Julian date, but Barycentric Dynamical Time (TDB)

Returns

[s] TDB - TT time difference.

Since

1.4

Author

Attila Kovacs

See also

tt2tdb_fp()

tt2tdb()

References tt2tdb_fp().

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