Julian Date

This online applet will convert a list of Barycentric Julian Dates in Barycentric Dynamical Time (BJD_TDB) to JD in UTC to an accuracy of 20 ms or the accuracy of double precision (~few ms) if the observatory is given. Its purpose is for precise scheduling of observations from ephemerides given in BJD_TDB. The BJD_TDB will never differ from JD_UTC by more than 10 minutes, so if your observing schedule is not very tight, this calculator is probably unnecessary. For A brief, non-technical explanation of BJD_TDB can be found here.

There is a programmatic interface to this applet. Here is an example that converts a list of BJD_TDBs to JD_UTC for alpha Centauri. The RA and Dec are always in decimal hours and the FUNCTION can be utc2bjd, bjd2utc or hjd2bjd. It does not support any observatories, so is only accurate to 20 ms.

BJD_TDBs

RA (J2000)		DEC (J2000)
	HH MM SS.S DDD.DDD		DD MM SS.S

-- Optional (default is geocenter) --

Earth-based observatory

-- or --

Latitude (degrees)	Longitude (degrees E)	Elevation (meters)

-- or --

Space Observatory**	Verbose

-- NOTE: this will return JD UTC! To calculate the BJD, go here. User inputs are NOT logged.

**If specifying the space observatory, please note that it requires a telnet session to HORIZONS, which will take at least 1 minute, and up to 2 minutes if the date range is large (>~ 1 year). If you want feedback during this time, check the verbose box. The telnet session is somewhat flaky, and there is limited error checking -- in particular, make sure the spacecraft was in flight during the dates specified. If it fails and you cannot determine why, download the source code and run it locally.

If you have made use of this calculator (or the source code) in a scientific paper, please cite our paper, which contains a more thorough explanation of the various corrections involved in this calculation.