[Kstars-devel] Predicting conjunctions

[Jason Harris]

It didn't work for Saturn and Pluto because Pluto has a very inclined
orbit, meaning it is usually far from the ecliptic.  Most other
planets are always near the ecliptic (but not the Moon).

I think you had the right approach, but it was only the first step:
you need to identify times when the two planets have the same
heliocentric longitude, and then check to see whether they have the
same latitude as well.

One question: what angular separation would you use to define a
"conjunction"?  Is there a standard definition for this?

The positions of the planets are computed using a sinusoidal expansion
series with hundreds of terms.  It should be possible to use only the
first ten or 20 terms in these series to get a quick estimate of where
a planet will be at a given time, then when you find a close
separation, you can go to the full solution to get the final answer.

regards,
Jason

On 3/11/08, Akarsh Simha <akarshsimha at gmail.com> wrote:
> Hi
>
>  I was trying to see if we could predict conjunctions of planets, so
>  that it could be incorporated into KStars.
>
>  What I thought was that we could first roughly calculate when the
>  occultation will happen next using circular orbits and such
>  approximations and then look around that point in time to find the
>  least separation.
>
>  However I found the trigonometry very tedious, so I tried some
>  approximation saying that the difference in the heliocentric
>  longitudes between the planets should go to zero. It happened to work
>  (mostly a coincidence!) for Mars and Jupiter. I was all excited, but
>  it failed for Saturn and Pluto - and it is a wrong algorithm.
>
>  Can someone suggest a better way of getting this?
>
>  Regards
>  Akarsh.
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