Beware Horizons Glitch

[bigmasterdrago]

I noticed tonight that when imputing the start time = 2021-10-16 UT-5, the output will be +5. The issue just began today as I noticed bad ephemerides for 2019 XS all of a sudden. Below is the output for 2021 TG14 as an example. It appears okay when simply generating an ephemeris for UT and not local time. I contacted Horizons concerning this weirdness.

Kenneth Drake

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Ephemeris / API_USER Sun Oct 17 19:24:04 2021 Pasadena, USA      / Horizons   
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Target body name: (2021 TG14)                    {source: JPL#3}
Center body name: Earth (399)                    {source: DE441}
Center-site name: (user defined site below)
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Start time      : A.D. 2021-Oct-16 00:00:00.0000 UT+05:00
Stop  time      : A.D. 2021-Oct-18 00:00:00.0000 UT+05:00
Step-size      : 60 minutes

[PMSchu]

Hi BMD,

That's a nasty error. I didn't specify a time zone in the file of elements that I posted for 2021 TX14, fortunately, so those element times are OK. Looks like Dennis will be rained out though. The iTelescope site in Chile wouldn't be any better than we northern hemisphere folks, though - daylight.

I'll be interested to hear what JPL has to say about that error. They're not expecting east longitudes for the observer by any chance are they?

Phil S.

[bigmasterdrago]

Got this email ~4pm today:
Ken,

This was fixed earlier today.

Negative signs in time zone corrections of the form UT-xx were ignored after
a recent Horizons update enabling UT/TT vector table production.

Over Oct 16-18, they instead returned as UT+xx, as indicated in the output
header.

Output for other zone correction forms 'UT*-' and 'UT+*', 'UTC*+*', and
'UTC*-*' were unaffected.

Thanks for pointing it out! Apologies the error.
-------------------------------------------------------------------------------
Jon Giorgini | Navigation & Mission Design Section
Senior Analyst | Solar System Dynamics Group
Jon.D.Giorgini@jpl.nasa.gov | Jet Propulsion Laboratory
-------------------------------------------------------------------------------

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When you do a search at Horizons for osculating elements, they always use UT exclusively. So no time correction will be excepted. Giorgini also sent a note to my warning at MLMP group.

[Dennis]

I noticed tonight that when imputing the start time = 2021-10-16 UT-5, the output will be +5. The issue just began today as I noticed bad ephemerides for 2019 XS all of a sudden. Below is the output for 2021 TG14 as an example. It appears okay when simply generating an ephemeris for UT and not local time. I contacted Horizons concerning this weirdness.

Kenneth Drake

*******************************************************************************
Ephemeris / API_USER Sun Oct 17 19:24:04 2021 Pasadena, USA      / Horizons   
*******************************************************************************
Target body name: (2021 TG14)                    {source: JPL#3}
Center body name: Earth (399)                    {source: DE441}
Center-site name: (user defined site below)
*******************************************************************************
Start time      : A.D. 2021-Oct-16 00:00:00.0000 UT+05:00
Stop  time      : A.D. 2021-Oct-18 00:00:00.0000 UT+05:00
Step-size      : 60 minutes

Hah, its good that someone is keeping and eye on these folks.

Good pick up BMD.

Cheers

Dennis