Celestia Forums

t00fri wrote:--Chris had forgotten about my two binary orbit files (visualbins.stc and spectbins.stc) in his installer *.iss file for Windows. So these were lacking accidentally in the recent 1.4.0pre versions. Since I now have included them, you will also get hundreds of new binary orbit data to play with...

Bye Fridger

This is great news! I'd been wondering about the status of your extended binary orbit files, as I seemed to recall there was some issue about deriving the mass ratios.

I do have another question, though. I presume the original catalog orbits are based on apparent time, i.e. as observed from earth. Should these be modified for Celestia to use actual time, adjusting for the light travel delay? That would be easy to include in the perl script that creates the files, would it not? Or did you already do it?

Of course, this would mean that the star positions would not appear correctly as seen from earth until light travel delay is implemented in Celestia. But that is already the case with solar system orbits, so at least it would be consistent.

- Hank

hank wrote:

t00fri wrote:--Chris had forgotten about my two binary orbit files (visualbins.stc and spectbins.stc) in his installer *.iss file for Windows. So these were lacking accidentally in the recent 1.4.0pre versions. Since I now have included them, you will also get hundreds of new binary orbit data to play with...

Bye Fridger

This is great news! I'd been wondering about the status of your extended binary orbit files, as I seemed to recall there was some issue about deriving the mass ratios.

I do have another question, though. I presume the original catalog orbits are based on apparent time, i.e. as observed from earth. Should these be modified for Celestia to use actual time, adjusting for the light travel delay? That would be easy to include in the perl script that creates the files, would it not? Or did you already do it?

Of course, this would mean that the star positions would not appear correctly as seen from earth until light travel delay is implemented in Celestia. But that is already the case with solar system orbits, so at least it would be consistent.

- Hank

Hank,

when I implemented LT a long time ago, I limited it to the solar system, else very strange effects could happen.
Also the philosophy in Celestia is a bit peculiar: the observer is considered as kind of a "Superman" not subject to the usual laws of physics. Physicists would call him a "test particle". The observer can move with /infinite/ speed throught the Universe, for example. So universal time as we measure it on Earth is also the time of Celestia's observer anywhere in the Universe. LT is just a correction for the solar system to correct for the finite speed of light if we want to correlate far distant events with the observer time.

In summary using universal time also for binary orbits is quite consistent within Celestia's philosophy of a "super" observer.

Bye Fridger

t00fri wrote:In summary using universal time also for binary orbits is quite consistent within Celestia's philosophy of a "super" observer.
Bye Fridger

Fridger,

I'm not sure I'm following what you're saying. Is it the case that binary star positions based on your files will not appear correctly when viewed from earth in Celestia?

- Hank

Fridger,

Perhaps I can clarify my question with an example. Suppose that Alpha Centauri B is observed from earth at periastron in 2005. Since it's 4 light years away, it was actually at periastron in 2001. Would your source catalogs specify an orbit with periastron in 2001 or 2005? Would your derived files for Celestia specify an orbit with periastron in 2001 or 2005? If the star were viewed from earth in Celestia, would it be seen at periastron in 2001 or 2005?

- Hank