Celestia Forums

Hello Celestians.
How precise are the positions of planets in celestia around the year zero ?
I wanted to find a conjunction of jupiter and saturn in pisces but jupiter was too far away from it ( Dec 4th 7 b.C.)
Or is this due to changes in calendar around 17... ?
Bye,
J?¶rg

Can it be the light travel delay ?
The difference of light travel time between jupiter-earth and saturn-earth is about 20 min.
I don??t know if pressing (-) Key includes light travel delay for both objects. It seems it doesn??t.
If it would then by pressing (-) the viewable distance between the objects should change.

Are you sure that the date was set correctly? Celestia uses negative years rather than BC and AD. So 1 BC would be the year 0, and 7 BC is the year -6.

--Chris

Yes, my mistake, thank you very much ! After making a little draft of a time-line I understand that the year zero doesn't exist .

I will try this when I'm back from work.

The other point with light travel delay is still not clear for me.
Depending on the object selected Jupiter and Saturn jump some degrees sidewards by pressing (-) but the distance (in degrees) stays the same.
So I understand it this way that l.t.d. is included only from the object selected but shown for both objects (Jupiter ans Saturn).
Is this the way it works ?

guest jo wrote:Yes, my mistake, thank you very much ! After making a little draft of a time-line I understand that the year zero doesn't exist .

I will try this when I'm back from work.

The other point with light travel delay is still not clear for me.
Depending on the object selected Jupiter and Saturn jump some degrees sidewards by pressing (-) but the distance (in degrees) stays the same.
So I understand it this way that l.t.d. is included only from the object selected but shown for both objects (Jupiter ans Saturn).
Is this the way it works ?

Just use the Search engine. I have explained it MANY times in the forum. Also it's apparently explained in Frank's manual Christophe wrote yesterday.

Bye Fridger

@cris:
Yes, with the corrected date jupiter and saturn come quite close together 3 times in the year 7 b.C. in pisces, thats wonderful.

Not so wonderful is that I still have problems understanding light travel delay in celestia ( or in principle).
I understand that (-) sets the position of a planet and its moons ( e.g. when seen from earth) to the place in the sky where we would see it in reality at the displayed time (and not where it really is).
I have read the manual and older posts to this item but I found nothing about viewing two planets with different distances at the same time.
I only want to know if celestia displays two planets like jupiter and saturn at the same time in the correct place when l.t.d. is switched on ?!

If the answer is "yes" then I have to think completely new about it.
From my understanding one of both planets always must be 5 degrees away from its supposed visible position from earth because of the difference in light travel of around 20 minutes.

Jo said:
"one of both planets always must be 5 degrees away from its supposed visible position from earth because of the difference in light travel of around 20 minutes."

That 5 degrees is too big. Let's calculate an estimate of how far Jupiter
goes in 20 minutes :

orbits 360 degrees in 12 years.
1 year is 525,600 minutes

20 minutes / 12 years = 20 / (12 * 525,600) = 0.000003

360 degrees * .000003 = 0.001 degree

So othe error due to light delay is not 5 degrees it is .001 degree

@globemaker
I admit you are probably right. ("probably" I use only cause I still have difficulties with understanding)
There must be a big error in my "theory".
My problem is the rotation angle of an observer on earth.
In 20 minutes earth turns 5 degrees so I thought that the angle between Jupiter and Saturn with l.t.d. on changes 5 degrees in comparison with l.t.d. off. In celestia it doesn't and somehow I get the feeling that I misunderstand something.
To start new one question: With what setting does celestia
display the planets seen from earth at their position visible in reality from here ? L.t.d on or off ?