Big, bright fast mover (7482) 1994 PC1

[PMSchu]

Hi Greg,

At some point I thought you said that the elements the farthest into the future would be kept, but maybe I got that wrong. This was back in summer of 2021 when I was first messing with the close approaches & trying to input several sets of elements so ST4 could chose the most appropriate one. That didn't work as you later explained. This was version R2 I think - ancient history. 

It's about time to download MPCORB again, since midnight tonight is the current standard epoch.

Phil S.

[theskyhound]

Phil,

Everything that needed to be said is in my post above.

[bigmasterdrago]

I'm thinking ST4 uses the element set closest to the date of requested ephemeris. That's why the positions in my table were much better for the daily and osculating vs the default in the bottom line (standard MPC import).

Yes, SkyTools keeps multiple sets of osculating elements and chooses the one that is best for the date that a position is being calculated for. But it is very important to remember that the epoch that the osculating elements were calculated for is just one factor in how accurate the elements will be. These close approachers are faint, so they can't be observed except when they come close to the earth. As a result, their orbits are not well known due to inadequate astrometric observations.

HORIZONS may appear to be more accurate during a close pass, but the real determination of accuracy is calculating the orbit using new observations as they become available, and new ones tend to come in just before the pass, so the accuracy of the elements gets better and better as that time comes closer. Always update your orbital elements just prior to the pass.

Without the assistance of Horizons/JPL/MPC we would be standing flat footed in our attempt to track these small close rocks down. As simple visual, and some imagers, we are working completely blind. By the simple assist of using the Uncertainty Parameter and Orbit Quality codes, we can decide which rocks to try and hunt down. I sometimes find that Horizons is lagging behind in getting timely info out but they are the source of elements along with those MPC guys.

I was thankful for the close pass of, finally, a bright, big rock but having been the victim of January weather, I was only able to make observations one night. I'll keep watching, searching and using all the tools that Greg bestows upon us as well as those at Horizons/MPC/JPL. They are the big guys that collect the observations that can be found at https://minorplanetcenter.net/db_search/...ct_id=7482. Over 800 of them.