<div dir="ltr"><div><div><div><div><div><div><div><div><div><div><div><div><div><div>Roy,</div><div><br></div><div>Ha! You are back :-)<br></div><div><br></div><div>I equally respectfully submit that the choice of "HJD" and "UT" is unwise (and actually foolish), for the following reasons:<br><br></div>- Heliocentric Julian Day is not an allowed representation of a time stamp, either in FITS, or in STC<br></div>- HJD is a confusing term in that it entangles (presumably, but not for certain) a time representation with a time reference position<br></div>- HJD is (probably) a misnomer (though, who knows?); I suspect it really refers to the solar system barycenter, rather than the heliocenter<br></div>- UT probably (but who knows?) is intended to refer to UTC, rather than UT<br></div>- UT is a poor choice to combine with anything that has JD in it, since it can become ambiguous<br></div>- If indeed the barycenter is intended to be the time reference position, TDB is the obvious choice, since UTC is not a linear timescale at the barycenter<br><br></div>In short: <br></div><div>It's an ambiguous (and lazy) shorthand for metadata that should be specified more precisely and explicitly.<br></div><div>Instead, use:<br></div>- Time scale = TDB<br></div>- Timestamp representation = JD (or MJD, or ISO 8601, if you like)<br></div>- Time reference position = BARYCENTER<br></div>It probably helps to also specify the solar system ephemeris used, like DE405<br><br></div>I may refer to the Time Metadata 101 that I circulated in May.<br><br></div>Cheers,<br><br></div> - Arnold<br></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr">-------------------------------------------------------------------------------------------------------------<br>Arnold H. Rots Chandra X-ray Science Center<br>Smithsonian Astrophysical Observatory tel: +1 617 496 7701<br>60 Garden Street, MS 67 fax: +1 617 495 7356<br>Cambridge, MA 02138 <a href="mailto:arots@cfa.harvard.edu" target="_blank">arots@cfa.harvard.edu</a><br>USA <a href="http://hea-www.harvard.edu/~arots/" target="_blank">http://hea-www.harvard.edu/~arots/</a><br>--------------------------------------------------------------------------------------------------------------<br><br></div></div></div>
<br><div class="gmail_quote">On Sun, Oct 15, 2017 at 11:02 AM, Roy Williams <span dir="ltr"><<a href="mailto:roy@roe.ac.uk" target="_blank">roy@roe.ac.uk</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear Colleagues<br>
We respectfully submit an IVOA Note about some proposed improvements to the VOEvent standard. We would appreciate some discussion on this email address and at the upcoming meeting in Chile.<br>
Thank you for your attention<br>
Roy Williams, Scott Barthelmy, Eric Bellm, Matthew Graham, Rob Seaman<br>
<br>
==================<br>
<br>
VOEvent Update: JSON and data models<br>
Author(s):<br>
Roy Williams, Scott Barthelmy, Eric Bellm, Matthew Graham, Rob Seaman<br>
<br>
UTL:<br>
<a href="http://ivoa.net/documents/Notes/VOEventJSON/index.html" rel="noreferrer" target="_blank">http://ivoa.net/documents/<wbr>Notes/VOEventJSON/index.html</a><br>
<br>
Abstract<br>
We propose an extension of the VOEvent format, to translate the packet from XML to JSON – with no semantic change. We also propose to use the VOEvent data model system to define three data-model Groups: “Light Curve”, “Associated Sources”, and “Followup Imaging”. This straightforward update of VOEvent simplifies the syntax and provides simple, standard representation of common astronomical datasets.<br>
</blockquote></div><br></div>