dateTimeToMJD | R Documentation |

The Julian Date (JD) of a given date and time is the number of days since noon of Monday 1st of January 4713 BC, including a fractional part. Modified Julian Date (MJD) are instead the number of days since 00:00 of November 17th, 1858. The difference JD and MJD for a given instant is always 2400000.5, which is the JD of the reference time for MJD.

This function calculates the MJD of a date and time, provided as a date-time character string in UTC time. The output refers by default to the MJD in UTC, but different time systems can be chosen: UTC (Coordinated Universal Time), UT1 (Universal Time), TT (Terrestrial Time) and TDB (Barycentric Dynamical Time).

dateTimeToMJD(dateTime, timeSystem="UTC")

`dateTime` |
Date-time string with the date and time in UTC corresponding to the provided geodetic coordinates. |

`timeSystem` |
Time system into which the MJD should be calculated. Should be one from "UTC" (Coordinated Universal Time; default), "UT1" (Universal Time), "TT" (Terrestrial Time) and "TDB" (Barycentric Dynamical Time). |

The MJD for the specified date and time in the chosen time system.

https://gssc.esa.int/navipedia/index.php/Julian_Date https://gssc.esa.int/navipedia/index.php/Transformations_between_Time_Systems

if(requireNamespace("asteRiskData", quietly = TRUE)) { # Let's calculate the MJD of the 12th of June, 2000 at 10:00:00 UTC time, in UTC MJD_UTC <- dateTimeToMJD("2000-06-12 10:00:00", timeSystem = "UTC") # Let's now calculate the MJD for the same instant in TDB: MJD_TDB <- dateTimeToMJD("2000-06-12 10:00:00", timeSystem = "TDB") # We can now calculate the difference in seconds, which matches the difference # between UTC and TDB for that day: (MJD_UTC - MJD_TDB) * 86400 }

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