Transit Collection

[selden]

Jestr,

I used Grant Hutchison's TLE to Celestia conversion spreadsheet. It's at http://www.lepp.cornell.edu/~seb/celestia/hutchison/spreadsheets.html

[Hoover]

On the page http://iss-transit.sourceforge.net/MissionAccomplished.html he said he was at lat 48.2562 lon 17.0280 at 10:09:17 UTC.

With the new ISS data the coordinates at 10:09:17 UTC (using the cel provided) are lat 48.06858 lon 17.01816

So while not to go too crazy on this, I still can't just go the lat/lon/time he provides, center the sun and see the ISS nearby.

Or am I making a mistake somehow?

[selden]

Hoover,

No, you're not doing anything wrong.

None of the available TLEs translate into Celestia orbital parameters which make the transit visible from the location where the transit actually was observed.

I don't know if it's a problem with the TLEs, with their translation to orbital parameters, or with Celestia's calculations. I could be persuaded that all of them have slight problems in accuracy and precision. The groundtrack of the ISS transit is extremely narrow, so high accuracy is required in everything, although I haven't bothered to try to figure out the standard errors involved.

I used the TLE that placed the ISS closest to the sun at the specified location and then, with "phase lock" enabled, moved the observing location until the transit was visible.

[Hoover]

Hm... Mr Thomas Fly can do it. I wonder if he'd be willing to tell his secret. Also the CalSky.com people claim to be able to do it but their site seems to be so busy I haven't gotten a readout yet.


Is there an easier way to change the observing location that using the pull down menu? If not, that would probably be useful. Perhaps be able to put the arrow keys into that mode?

One for the wish list. I wish it was possible to display lat lon altitude information for a body even if you have selected something else. If the lat lon were in a city it could be displayed as well.

Actually if the first suggestion were possible you'd almost have to be displaying lat lon alt so you'd know where you were going.


Yet another thought. Perhaps be able to select and mark the shadows of objects. e.g. in this case you could select the shadow of the ISS. You go to it and there you are, beneath the transit all the time! e.g. you select the shadow of Europa and follow it on the face of Jupiter. The only question is where do you display the marker for the shadow when its not on any body. Then it might have to be displayed in the plane of the area around that body. This would be very cool to track the center of the shadow of the moon around the earth and watch it move. What pattern does it make?

Just spewing a few of my last thoughts before I'm off for a few weeks. I'll probably go silent now. Just hope something interesting happens.

[Calculus]

I was able to reproduce the Moon Occulting the Pleiades. I saw the time and date in Calculus' gallery. But there's no way I could make the background stars look the same!

1972 Moon Occults the Pleiades
cel://PhaseLock/Sol:Earth/Pleiades/1972-03-20T03:14:35.22474?x=wHe9il/wMe2tDA&y=sdMHq5VF/P///////////w&z=fcfAUXtVlA&ow=0.965101&ox=-0.037095&oy=0.259238&oz=0.000658&select=Pleiades&fov=3.126083&ts=1.000000<d=0&rf=57235&lm=-512

This is just because I used my own bilboard texture for the pleiades!

[granthutchison]

I don't know if it's a problem with the TLEs, with their translation to orbital parameters, or with Celestia's calculations.

You also need to recall that Celestia's modelling of the Earth's rotation is far from perfect. While the effect is generally trivial in present-day simulations, the ISS transit is exactly where you might expect the problem to reveal itself - a small error in the surface position of the Earth, looking at a nearby object (the ISS) against a much more distant one (the Sun).

[t00fri]

Hi all,

perhaps it's instructive to see how the Internet updating and highly accurate display of satellite transits was/is realized in XEphem (already since years ...):

First step: In the dialog below just push the respective 'get' buttons then the latest TLE's are downloaded, stored and converted into XEphem format within seconds:



Next there is a variety of ways to display (and observe) the satellite transits. One example is this, in case of ISS



Unfortunately, we seem to have largely stopped discussing new interesting lines of development ...

Bye Fridger

[selden]

Fridger,

One problem(?) is that Celestia does not need to have this capability built into it.

It should be "trivial" for an interested person to implement an external package (Web page?) that would invoke software to download the TLEs, convert them to Celestia's SSC format, write an appropriate SSC file, and then optionally restart Celestia with an appropriate viewpoint.

[t00fri]

Fridger,

One problem(?) is that Celestia does not need to have
this capability built into it.

It should be "trivial" for an interested person to implement an external package (Web page?) that would invoke software to download the TLEs, convert them to Celestia's SSC format, write an appropriate SSC file, and then optionally restart Celestia with an appropriate viewpoint.

Selden,

no, there is no "need", but in practice the procedure you
mention is rather time consuming, if there is no
dedicated tool. The best form for such a tool is
something to be discussed among people who
know how to write code in Celestia or to produce
respective add-ons...


For a quantitative observation of satellites from
your backyard (at the correct time!) you have to update
the TLE's every 1-2 days! I have been involved in
extensive testing of this stuff in the context of XEphem.

So I know from experience.


The point is that in XEphem a few clicks allow you to
update, store and convert all requested satelite
parameters virtually in less than a minute! No fiddling
around with EXEL sheets etc.


At the same time you can download, update and convert
the huge asteroid data files as well....


I find that tremendously handy...


Bye Fridger

[selden]

Fridger,

I was assuming that the TLE conversion would be entirely handled by the "Web page program", presumably written in Java for portability.
No spreadsheet should be involved.

Is the code (or its documentation) used by XEphem available?
I'm wondering if its design could be used, not the code itself.

[t00fri]

Fridger,

I was assuming that the TLE conversion would be entirely handled by the "Web page program", presumably written in Java for portability.
No spreadsheet should be involved.

Is the code (or its documentation) used by XEphem available?
I'm wondering if its design could be used, not the code itself.

Selden,

XEphem is Open Source. I have of course the sources.
They can be downloaded. Permission is needed from Elwood if parts of the code are to be used.

The question is why you think a separate WEB utiliy is more suitable. We are really talking about a relatively small utility. It would be quite handy, if one is playing with Celestia (or XEphem). You just click from inside the program and all work is done. No need for going to your browser first, loading ...and all that.

I still remember the frequent resistance, people had against (KDE-)Celestia's outbound info utility that after a click on an object, fires the browser and gets you to the respective page in the Strassbourg central astronomy archive...

Bye Fridger

[selden]

Selden,

XEphem is Open Source. I have of course the sources.
They can be downloaded. Permission is needed from Elwood if parts of the code are to be used.

Thanks for the info! (although I'm unlikely to do anything with this: I'm still working on various DSC Addons for Celestia...)

The question is why you think a separate WEB utiliy is more suitable. We are really talking about a relatively small utility. It would be quite handy, if one is playing with Celestia (or XEphem). You just click from inside the program and all work is done. No need for going to your browser first, loading ...and all that.

I suggested a separate utility because then it is possible (in principle) for anyone to write the program. It wouldn't have to be written by someone on the Celestia development team. It needn't actually be an HTML page, of course. It's just that I'm much more familiar with using HTML for a user interface than I am with creating GUI windows in Java (which I don't know at all).

Of course, if Lua I/O is available in the next version of Celestia, then it probably should be written in that language instead of Java.

I still remember the frequent resistance, people had against (KDE-)Celestia's outbound info utility that after a click on an object, fires the browser and gets you to the respective page in the Strassbourg central astronomy archive...

But that's exactly what this is! So why are you objecting?

[t00fri]

Selden,

XEphem is Open Source. I have of course the sources.
They can be downloaded. Permission is needed from Elwood if parts of the code are to be used.

Thanks for the info! (although I'm unlikely to do anything with this: I'm still working on various DSC Addons for Celestia...)

The question is why you think a separate WEB utiliy is more suitable. We are really talking about a relatively small utility. It would be quite handy, if one is playing with Celestia (or XEphem). You just click from inside the program and all work is done. No need for going to your browser first, loading ...and all that.

I suggested a separate utility because then it is possible (in principle) for anyone to write the program. It wouldn't have to be written by someone on the Celestia development team. It needn't actually be an HTML page, of course. It's just that I'm much more familiar with using HTML for a user interface than I am with creating GUI windows in Java (which I don't know at all).

Of course, if Lua I/O is available in the next version of Celestia, then it probably should be written in that language instead of Java.

I still remember the frequent resistance, people had against (KDE-)Celestia's outbound info utility that after a click on an object, fires the browser and gets you to the respective page in the Strassbourg central astronomy archive...

But that's exactly what this is! So why are you objecting?

Selden,

...no I am not objecting. I always was a vigorous defender of this "outbound" philosophy. But I also learned that the general acceptance does not seem to be "overwhelming"...

I guess, it's an easy job for LUA, once some ftp type interfacing has been implemented. From my Maple expertise I happen to know plenty of "Lua" (you remember about the "accidental isomorphy";-) of these two scripting languages...), so I think I can judge quite well...

Bye Fridger

[Hoover]

While I was on vacation a picked up the August 2004 issue of Sky and Telescope. It just so happened there was an article about a Mercury and Venus Simultaneous Transit which will occur in the year AD 69,163.

The article refers to the Journal of the British Astronomical Association as the source. But unfortunately I can't point you to any information on how they did it (nor do I know either), the Journal isn't posted online in its entirety. And S&T (geesh) makes you pay for downloading of articles so I can't even show you that.

There were two events listed. The AD 15,232 of a simultaneous total solor eclipse during the Transit of Venus, and the observation above. Unfortunately, these can't be confirmed with Celestia as I have tried, but the planets (and moon) aren't in the right places. If anyone else is curious here are the cel's I used.

15232 Transit of Venus and Total Solar Eclipse
cel://PhaseLock/Sol:Earth/Sol/15232-04-05T20:56:51.47155?x=t1Zl9KmtwQauDA&y=QiA338JxxQE&z=S2jBBZT5QN3+/////////w&ow=-0.658079&ox=-0.188787&oy=-0.707506&oz=0.175288&select=Sol&fov=1.919145&ts=1.000000<d=0&rf=36787&lm=-382

69163 Transit of Mercury and Venus
cel://PhaseLock/Sol:Earth/Sol/69163-07-26T00:12:12.23308?x=F8kGpler/Rm6DA&y=JWpbOWyXge///////////w&z=KacqJKpspd3w/////////w&ow=0.112993&ox=0.189835&oy=0.974994&oz=-0.024125&select=Sol&fov=1.410327&ts=1.000000<d=0&rf=36787&lm=-382

Edit: The articles states this caveat. These dates are expressed in Dynamical Time; exact dates will depend on the length of Earth's day, which we can't know in advance, and on whatever calendar adjustments our descendants might make.

[chris]

There were two events listed. The AD 15,232 of a simultaneous total solor eclipse during the Transit of Venus, and the observation above. Unfortunately, these can't be confirmed with Celestia as I have tried, but the planets (and moon) aren't in the right places. If anyone else is curious here are the cel's I used.

The VSOP87 series that Celestia uses for the orbits of the eight major planets are only meant to be valid within a limited range of dates. For dates before 2000 BCE or after 4000 AD, Celestia just uses elliptical orbits instead. The ellipses aren't accurate, but they do have the advantage of keeping the planets in roughly sensible orbits, whereas the series orbits break down and scatter planets all over the solar system after a while. Celestia is too conservative now when falling back to elliptical orbits and the VSOP87 orbits could be used further into the future. I'll investigate to see whether they can reproduce the AD 15,232 event. The simultaneous transit in 69163 is almost certainly out of reach.

--Chris

[ElPelado]

AFAIR the venus transits and mercury transits occur in different times of the year, so that makes impossible to have a simultanious transit, but I am not sure, maybe in a 'couple' (:lol:) of years that will change...

[Hoover]

What makes the orbits change over time? It seems to be accepted that the orbits change enough that simulatenous transits can occur eventually. But what I'd like to know is, what did they do to calculate out that far that Celestia cannot do? Is it that they have more computational power or they used different formulas?

My doubts are in considering that they might have done something to "make it work" as it were.

[t00fri]

What makes the orbits change over time? It seems to be accepted that the orbits change enough that simulatenous transits can occur eventually. But what I'd like to know is, what did they do to calculate out that far that Celestia cannot do? Is it that they have more computational power or they used different formulas?

My doubts are in considering that they might have done something to "make it work" as it were.

Well there are for instance the direct integration results by NASA that are presently used as a "CPU-intensive" benchmark for the upcoming VSOP2000 results mainly for the ephemerides of the moon. You probably know that these were not part of VSOP87...

Bye Fridger

[Hoover]

Is there any chance Celestia will be given this kind of accuracy for going ahead 10's of thousands of years? It should be possible, but is it feasible?