Celestia is open source.
This means that you can copy it to make your own program which includes whatever features you want to try out. You can't call the result Celestia, of course.
Mostly Harmless is a program based on Celestia which at one point included gravitational effects applied to the observer. Contact its author for details.
Capt Rooster wrote:Honestly, noone here is an expert at Physics. If that was the case, Celestia would not be as readily available and this person would be working for government agencies that would not allow them to be online here. .
Fortunately you are incorrect about some of your assumptions.
Fridger Schrempp
is a professional physicist and knows whereof he writes. Don't take my word for it. Do a Web search.
Not all physicists work for government agencies. Many of them work for educational institutions. Others work for corporations. I know several who work on Wall Street, applying what they've learned to other ends.
None of them are prevented from contributing their free time to publicly available software projects like Celestia.
People working for NASA contribute to Celestia, and have even done it as part of their jobs. Examples of their work are at
http://learn.arc.nasa.gov/planets/ and
http://exp.arc.nasa.gov/downloads/
Educational institutions have used Celestia's source code as a teaching tool, with students modifying it to run in other environments. One example is at
http://www.lsi.usp.br/~paiva/glass/glass.htm
It shows the results of porting Celestia to the Cave envrionment. (The Cave is a room which provides an immersive 3D environment. Quite a few universities have Caves in their graphics facilities.)
However, Chris Laurel is the primary author of Celestia and makes the final decisions on what features get included.
I hope this clarifies things a little.