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Old 12-01-2020, 04:14 PM
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gary is offline
Join Date: Apr 2005
Location: Mt. Kuring-Gai
Posts: 5,406
Originally Posted by Dennis View Post
Thanks Barry, you nailed it, the comet is clearly visible centre frame.

I used 4 programs to plot the position; The Sky X Pro, Starry Night Pro 8, Sky Safari and SkyTools 4 and all of them indicated positions several degrees apart.

I made sure that I refreshed all the Comet Elements for each program via downloads and checked that my observing site and details were all the same and correct, so not sure why the variation - I suspect they must use different sources?


Hi Dennis,

The problem originates at the Minor Planet Center (MPC).

2I/Borisov has a very, very high orbital eccentricity (in the order of ‎3.3575)
and the orbital elements are just the solution for a two-bodied problem.

The orbit is sufficiently perturbed that unless you are using very recent
orbital elements (check the epoch), the computed position will be
degrees out.

Something is up at the MPC. The elements they have been publishing
for the software packages for some comets have epochs that are
weeks and months out of date compared to the recent epochs used
for the orbital elements they also publish separately as raw data.

The asteroid elements for the software packages are even worse
where they were last computed for epochs in 2018.

Many of these orbits have been perturbed since then.

They had some computer system failures some time back and things have
been out of kilter since then.

The workaround is to use the data either they or JPL supply when
you examine an individual object and synthesise the elements from that.

How you then load your own elements into the package of choice I will
leave as an exercise for you but it may not be possible for all packages.

Alternatively, just use the MPC web page that allows you to compute the
RA/Dec position at multiple points in time, say every 5 minutes in the evening.
Those positions are accurate.
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