See Astro.Time.julian_day_from_date/1.

Adds the requested minutes to a date returning a datetime in the UTC time zone

Arguments

• minutes is a float number of minutes since midnight

• date is any date in the Gregorian calendar

Returns

• a datetime in the UTC time zone

Returns the datetime for a given Julian day

Arguments

• julian_day is any astronomical Julian day such as returned from Astro.Time.julian_day_from_date/1

Returns

• a DateTime.t in the UTC time zone

Example

iex> Astro.Time.datetime_from_julian_days 2458822.5
{:ok, ~U[2019-12-05 00:00:00Z]}

Returns the number of seconds since 0001-01-01 in the Gregorian calendar.

Arguments

• datetime is any DateTime.t since 0001-01-01in the Calendar.ISO calendar

Returns

• An integer number of seconds since 0001-01-01

Converts a float number of hours since midnight into {hours, minutes, seconds}.

Arguments

• time_of_day is a float number of hours since midnight

Returns

• A {hour, minute, second} tuple.

Examples

iex> Astro.Time.hours_to_hms 0.0 {0, 0, 0}

iex> Astro.Time.hours_to_hms 23.999 {23, 59, 56}

iex> Astro.Time.hours_to_hms 15.456 {15, 27, 21}

Returns the day number for January 1st, 2000

Returns the Julian centuries for a given Julian day

Arguments

• julian_day is any astronomical Julian day such as returned from Astro.Time.julian_day_from_date/1

Returns

• the astronomical Julian century as a float

Returns the astronomical Julian day for a given date

Arguments

• date is any Calendar.date

Returns

• the astronomical Julian day as a float

Example

iex> Astro.Time.julian_day_from_date ~D[2019-12-05] 2458822.5

Returns the Julian day for a given Julian century

Arguments

• julian_century is any astronomical Julian century such as returned from Astro.Time.julian_centuries_from_julian_day/1

Returns

• the astronomical Julian day as a float

Returns the modified Julian day for a date

Arguments

• date is any Calendar.date

Returns

• the modified Julian day as a float

Notes

A modified version of the Julian date denoted MJD is obtained by subtracting 2,400,000.5 days from the Julian date JD,

The MJD therefore gives the number of days since midnight on November 17, 1858. This date corresponds to 2400000.5 days after day 0 of the Julian calendar.

Converts a float number of hours since midnight to a DateTime.t()

Arguments

• time_of_day is a float number of hours since midnight

• date is any Calendar.date()

Returns

A DateTime.t() combining the date and time_of_day in the UTC timezone.

Returns the offset in float days for a given moment and time zone.

Example

# Returns a 1 hour offset as a fraction of day
iex> t = Cldr.Calendar.date_to_iso_days(~D[2021-08-01])
iex> Astro.Time.offset_for_zone t, "Europe/London"
0.041666666666666664

Converts a number of seconds since midnight into {hours, minutes, seconds}.

Arguments

• time_of_day is a number of seconds

Returns

• A {hour, minute, second} tuple.

Examples

iex> Astro.Time.seconds_to_hms 0.0 {0, 0, 0}

iex> Astro.Time.seconds_to_hms 3214 {0, 53, 34}

iex> Astro.Time.seconds_to_hms 10_000 {2, 46, 39}

Converts a terrestrial datetime to a UTC datetime

Arguments

• datetime is any UTC datetime which is considered to be a Terrestrial Time.

Returns

• A UTC datetime adjusted for the difference between Terrestrial Time and UTC time

Notes

Terrestrial Time (TT) was introduced by the IAU in 1979 as the coordinate time scale for an observer on the surface of Earth. It takes into account relativistic effects and is based on International Atomic Time (TAI), which is a high-precision standard using several hundred atomic clocks worldwide. As such, TD is the atomic time equivalent to its predecessor Ephemeris Time (ET) and is used in the theories of motion for bodies in the solar system.

To ensure continuity with ET, TD was defined to match ET for the date 1977 Jan 01. In 1991, the IAU refined the definition of TT to make it more precise. It was also renamed Terrestrial Time (TT) from the earlier Terrestrial Dynamical Time (TDT).