Skip to main content

WEbObs date convention

2 posts / 0 new
Last post
PVEA's picture
WEbObs date convention

I did not find a forum topic about WebObs dates interpretation so I have started one.

My recent works require that my photometric data should be in HJD instead of JD. Still I am not ready to submit these data to WebObs but I did only the trial submission. The purpose was to check how WebObs interpret HJD. To submit data in WebObs the following conditions should be perform:

  1. For photometric observations, the uploaded file must be format according to the AAVSO Extended Format.
  2. In the AAVSO Extended Format the format of the DATE should be converted from UT to one of the following formats:
  • JD: Julian Day
  • HJD: Heliocentric Julian Day
  • Excel

In the attached screenshot, one can see that in my trial submission the HJD dates are still described as JD.

The question is:

  1. If all the dates in WebObs are submitted in different way (JD, HJD or EXCEL), how one can use the downloaded from WebObs data if they consist only JD description?
  2. How one can be sure that using this data presumably as JD will not do a modeling error, the epoch and period etc.?

If I miss something, please just point it to me.


HQA's picture

Hi Velimir,

I don't see that anyone at HQ answered your question, so I'll give it a try.  What I say may or may not be correct; if you need more information, you need to send an email to HQ.

There are two fields in the International Database for date:  JD and HJD.  If you submit an observation that uses JD, then the JD field gets filled in and the HJD field is left blank.  If you submit an observation that uses HJD, then the HJD field gets filled in and WebObs converts HJD to JD and fills in that field too.

You can see this by going to the download page and downloading your observations; the appropriate fields will be filled in.  I'm not sure what WebObs itself will display, so trust the download page more.

The correct date format is actually HJED, using barocentric time.  The AAVSO started out as a primarily visual organization looking at long period variables where the +/-8min offset of HJD made little difference, and calculating JD was much easier.  Now that many of our observations are digital, and often of rapidly varying objects, the guidelines for time calculation for observation submissions should probably be revisited.


Log in to post comments
AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484