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

Mon Jun 4 19:06:02 CEST 2007

Hi.

I see that this logic works very fast.

But how would you be sure that the algorithm hasn't missed one of
those possible occultations?

And how do we keep these "occultable" objects, i.e. bright stars,
planets? Do we put them in a QList or QHash or some such thing?

How I picturize the occultation module is that it should be able to
predict occultations of a fixed body against a number of possible
other bodies. These other bodies could be bright stars, other planets,
or DSOs. I should also be able to select a fixed object for the second
object, like, for instance ask when the next occultation of Moon and
Mars will be. I should also be able to give time ranges for prediction
of occultations.

I also feel it'd be nice if we could extend the occultations tool to
also do rendezvous predictions, like the recent Comet 73P and Ring
Nebula etc. I picturize this as an "occultation" where the angular
separation between the objects is set to something arbitrary, say the
FOV of your telescope. That could help you predict, for instance, when
Comet 2P/Encke and Andromeda Galaxy would again appear in the same FOV
in the telescope, which would be a wonderful and unique extension to
the same occultation tool.

Any ideas?

On 6/4/07, Jason Harris <jharris at 30doradus.org> wrote:
> 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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> > > > When replying, please edit your Subject line so it is more specific
> > > > than "Re: Contents of Kstars-devel digest..."
> > > >
> > > >
> > > > 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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-- 
Regards,
     Akarsh
http://www.bas.org.in
http://www.nascent-technologies.com