Celestia Forums

I would like to look at the earth as if I'm standing on the sun,
meaning that I would like to see the slow annual drift of the earth axis
with respect to the sun's orbit.
I am sure it can be done, but just can't figure it out

Ren?©

goto the center of the Sun (it's invisible from the inside)
track Earth
speed up time

It'll help if you include an Addon that draws a line through the Earth's axis.
One is available at http://www.lepp.cornell.edu/~seb/celest ... les.html#5

It works Selden , it is just that if I set the time to NOW the vision towards the earth is blocked by something big (mercury/venus ??),
is there anyway to overcome this behaviour ??

Ren?©

Ren?©,

You have to determine what it is that's blocking your view.
Since I don't know where your viewpoint is located, I can't guess.
However, I don't know of anything that'd be likely, other than the Sun itself.

selden wrote:Ren?©,

You have to determine what it is that's blocking your view.
Since I don't know where your viewpoint is located, I can't guess.
However, I don't know of anything that'd be likely, other than the Sun itself.

Yep; it seems to be the sun itself; how do I get to the middle of the sun,
and why should the sun be transparant when viewed from the middle ??


Ren?©

Hmmm. Going directly to the center of the Sun is a little more difficult than I thought.

One way is to create an invisible planet there. Here's an SSC catalog:


Hmm. It still doesn't work as well as I'd like.

3D objects in Celestia usually are invsible from the inside because of the design of their 3D models: their surface normals all point outward. Celestia draws a surface (makes it visible) only when its surface normals point toward the viewpoint. Unfortunately, since Celestia draws a photosphere around stars, that is still visible as a yellow glow. Also, I see flashing solar surfaces being drawn on my system. I suspect there's a bug in Celestia related to drawing a star from the inside.

It seems to work reasonably well when I define a dummy object that orbits just above the Sun's surface with the same orbital period as the Earth. Following that object and Tracking the Earth avoids the problems mentioned above. If you turn on the "Celestial Grid", you can see direction markers drawn around the Earth when you increase the magnification. They help to see how the Earth tips back and forth. They're drawn entirely behind the planet, though, so that the polar marks aren't drawn coming out of the Earth's poles.

Thanks Selden , that last piece of code did the trick.
Now to make things a bit more challenging (for you that is):
How about precession of the earth's axis, the one moving the axis around
in thousands of years: is it possible to view that rotation or the effect of it also ??


Ren?©

Unfortunately, not accurately.

As I understand it, it isn't handled properly when using the accurate VSOP-87 Earth and Moon orbits. However, if you're willing to use the less accurate Keplerian orbits (comment out the lines starting with CustomOrbit in data\solarsys.ssc), then you can add a PrecessionRate statement in the Earth's definition and it'll do something reasonable.


Unfortunately, I don't recall the units. I think it's degrees/day. (See the comment in solarsys.ssc about the PrecessionRate used for Hyperion.)

Thanks, I will try it.
I am always amazed to see
how flexible this program has been written,
just by commenting out things or adding a few lines
the behaviour can be tuned to ones needs.

Cheers for you programmers ...


Ren?©