Hi Ron,
If you generate the ephemeris within Find_Orb, you'll get a numerically integrated
ephemeris either way. Switching the element display won't actually affect output;
you'll just get two element sets representing exactly the same orbit.
If you put those orbital elements into Guide (or other software that _doesn't_
numerically integrate orbits), then all of a sudden, the heliocentric and geocentric
elements will _not_ be the same. (Except at the epoch.) For dates near the epoch,
Guide using geocentric elements will be within an arcminute or two of Find_Orb's
numerically integrated result. That arcminute will reflect the sun and moon gradually
tugging 2012 DA14 away from the earth.
Feed heliocentric elements into Guide, and it'll be the effects of the earth and
moon that are ignored, which are a heck of a lot more important for an object that's
coming within 34000 km of the earth's center. Your ephemeris will still be exact for
the moment of epoch, but will quickly diverge from reality.
-- Bill
On 01/28/2013 12:21 PM, rbaker7356 wrote:
> I've been following the discussion on MPML about the upcoming close approach of 2012 DA14. Bill has already addressed this in detail. But when more observations are available I'd like to be able to create updated geocentric elements with Find_Orb which can then be used in Guide.
>
> I'm using the development version of Find_Orb (Jan 16 2013). With the current list of observations from the MPC and the epoch set to 2013 Feb 15.8, I can get Find_Orb to determine geocentric elements with a reasonable mean residual. But the ephemeris appears to be the same as an ephemeris produced when the 'heliocentric orbits only' box is checked.
>
> Once the geocentric elements are created, how can an ephemeris based on those geocentric elements be produced?
>
> Thank you,
> Ron Baker
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