[Kstars-devel] Kstars-devel Digest, Vol 46, Issue 8

[Jason Harris]

Hello,

I think you're right; the only way to predict occultation events is to advance 
the time in small steps, and check whether the angular separation of the 
bodies is smaller than their angular size.

However, there are ways to speed up the process.  You can take a large 
timestep, and see if a linear approximation of the body's path carries it 
near any bright stars.  If so, then you can estimate when a potential 
occultation would occur, set the clock to that time, and check the position.  
The new position will either (a) be in occultation, (b) exclude the 
possibility of occultation, or (c) be placed "before" or "after" a potential 
occultation.  In case (c), we would predict a new occultation time based on 
the body's positions at known times bracketing the target star, set the clock 
to that time and try again until we got (a) or (b).

This is called a "predictor-corrector" search.  It is much faster than just 
advancing the clock by small steps over the whole interval.  When the target 
object that may be occulted is another planetary body (rather than a star), 
the calculation will be more complicated, but the general strategy still 
applies, I think.

regards,
Jason

On Monday 04 June 2007 02:43, Akarsh Simha wrote:
> I'm sorry... please ignore my previous reply in this thread - it makes
> no sense whatever and I was confused while writing that.
>
> How would one predict occultations though?
> The only way I can think of is keep increasing (or decreasing) the
> time in certain small steps and check if the occultation is going to
> happen. But that will be extremely slow, or so I think.
>
> A modification I see to the above is that we ask the user to input a
> time range and then do some kind of a smart search which also applies
> some logic to guess an estimate and then search around that.
>
> Any better ideas?
>
> On 5/28/07, Akarsh Simha <akarshsimha at gmail.com> wrote:
> > Ok. Thanks for that. I guess I should be able to do it easily if the
> > heliocentric longitudes are computed somewhere. I'll take a look into
> > this.
> >
> > On 5/28/07, brian hurren <brianhurren at yahoo.com> wrote:
> > > Akarsh, have a go at writing a class for occultations.
> > >
> > > kstars-devel-request at kde.org wrote:
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> > > Today's Topics:
> > >
> > > 1. Quite a few bugs (Akarsh Simha)
> > >
> > >
> > > ----------------------------------------------------------------------
> > >
> > > Message: 1
> > > Date: Sun, 27 May 2007 00:55:29 +0530
> > > From: "Akarsh Simha"
> > > Subject: [Kstars-devel] Quite a few bugs
> > > To: kstars-devel at kde.org
> > > Message-ID:
> > >
> > > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> > >
> > > Hello
> > >
> > > I am new to this mailing list. I am Akarsh Simha, a student of
> > > Physics, from Bangalore, India and an amateur astronomer. Am not very
> > > well acquainted with Linux programming, though I can do some coding in
> > > C++.
> > >
> > > I was looking through KStars and found a few bugs, which I'm posting
> > > here:
> > >
> > > 1. The highlighted constellation boundaries do not coincide with the
> > > actual boundaries when zoomed in.
> > > 2. Io and Europa are not displaying correctly
> > > 3. Constellation names in the object identification that pops up when
> > > you right click on the object shows the constellations' three letter
> > > abbreviations instead of the name.
> > > 4. I opened the Object Details dialog and clicked on the image to do
> > > an image search. After I closed the image search dialog, I got a
> > > segmentation fault. I have saved the Backtrace that KDE generated.
> > > 5. It seems like there is no display symbol for asteroids. I feel that
> > > the symbol for comets need to be something more meaningful.
> > >
> > > Regards,
> > > Akarsh
> > >
> > >
> > > ------------------------------
> > >
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> > >
> > > End of Kstars-devel Digest, Vol 46, Issue 8
> > > *******************************************
> > >
> > >
> > >
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> > --
> > Regards,
> >      Akarsh
> > http://www.bas.org.in
> > http://www.nascent-technologies.com

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