Re: Positional uncertainty PA value?

Tony,

I probably shouldn't have confused things with 2014 VQ! All the other objects I've tried (single opp NEOs last observed a few years ago) like 2009 VZ have very stable PAs of uncertainty and as originally mentioned, MPC and NEODyS agree closely, FO doesn't.

I think you're very likely right that FO is counting these uncertainty PAs clockwise from N, the opposite to the MPC, even though the direction of motion on the sky matches the MPC values and is counting anticlockwise from N.

Peter

---In find_orb@yahoogroups.com, <tony.evans@...> wrote :

Peter, I think the problem with a situation like this that the uncertainty is small (FO says 0.1") and the PA of the uncertainty is itself uncertain. It can vary hugely depending on exactly which set of observations FO/MPES are using. The frequent arrival of new observations and revisions of the elements will cause big changes in the uncertainty PA.

When using FO, the exact settings will also cause differences - contents/use of sigma.txt file. Filter setting, time of download of obs DB etc.

This morning (9:00 UT) I get an uncertainty PA of 23.0 from the MPES for J95 at 1:00 on 11/11.

Using FO, and depending on which observations I select, sigma.txt, filter, I can get uncertainty PAs that range from 4 to 157 for J95 at 1:00 on 11/11.

The objects I originally tried had big uncertainties 2014 MQ67 and 2011 JU2 so the exact settings make little difference and MPES/FO should get near identical results.

Tony