Timeline for Why is there a 38.6 km Earth-Moon distance difference between Ephemeris types "Observer table" and "Vector table" on Horizons Web Application?
Current License: CC BY-SA 4.0
18 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| S Dec 14, 2022 at 16:28 | history | bounty ended | Cornelis | ||
| S Dec 14, 2022 at 16:28 | history | notice removed | Cornelis | ||
| Dec 7, 2022 at 0:00 | history | tweeted | twitter.com/StackSpaceExp/status/1600278996066996226 | ||
| Dec 6, 2022 at 21:41 | answer | added | Greg Miller | timeline score: 2 | |
| S Dec 6, 2022 at 17:44 | history | bounty started | Cornelis | ||
| S Dec 6, 2022 at 17:44 | history | notice added | Cornelis | Authoritative reference needed | |
| Dec 6, 2022 at 17:16 | comment | added | PM 2Ring | Maybe give it a few more days. You never know, someone might have a perfectly logical explanation. | |
| Dec 6, 2022 at 16:10 | comment | added | PM 2Ring | It's not just a Moon thing. Check out Mercury! i.sstatic.net/9gR2J.png I'll polish up my plotting code & add it to my answer. | |
| Dec 6, 2022 at 15:19 | comment | added | PM 2Ring | However, there is another difference between the two table types. By default, Observer tables use UTC, but Vector tables use TDB. But it's possible to explicitly state which time scale you want to use. So the numbers you appended to the end of your question have an extra difference caused by that time scale difference of ~40.455 seconds. | |
| Dec 6, 2022 at 14:28 | comment | added | PM 2Ring | @GregMiller You can request light-time corrected vector tables, and the result is virtually identical to the range reported in the observer table (but with more digits), as I mention in my answer | |
| Dec 6, 2022 at 13:35 | comment | added | Greg Miller | One possible source of the difference is the observer tables are "apparent" coordinates, where the vector table are geometric coordinates (e.g. not adjusted for light time, annual aberration, etc). I also noticed the vector table lists the "Center-site name" as "Body Center" for the vector table and "GEOCENTRIC" for the observer table. Since the Earth's center vs center of mass is about 40Km, that would align with different centers being used. | |
| Dec 6, 2022 at 10:55 | history | edited | Cornelis | CC BY-SA 4.0 |
added 31 successive days
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| Dec 5, 2022 at 11:18 | comment | added | PM 2Ring | Maybe we should ask someone at JPL about this, maybe even Jon Giorgini... :) | |
| Dec 5, 2022 at 9:22 | comment | added | PM 2Ring | @BobWerner It's a mystery! BTW, Delta T at that time was only ~40.455 s. I rediscovered that since Oct 2021 Horizons allows you to specify UT or TT (not just TDB) for vector tables, elements tables must use TDB. | |
| Dec 5, 2022 at 9:17 | answer | added | PM 2Ring | timeline score: 2 | |
| Dec 4, 2022 at 19:44 | comment | added | Bob Werner | I had thought the problem was a difference in time scales. The Observer Table time is expressed as UT (i.e. UTC), while the Vector Table time is TDB. There is a difference of 69.184 seconds between the two (UTC + 69.184 seconds = TDB). However, when I attempt to compensate, the range problem that you highlight does not disappear. | |
| Dec 4, 2022 at 17:45 | history | edited | Cornelis | CC BY-SA 4.0 |
added 12 characters in body
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| Dec 4, 2022 at 17:40 | history | asked | Cornelis | CC BY-SA 4.0 |
