I read What would make scientists realize they were on a flat world?, and I decided to make a similar one.
Scenario: While poking around in an alien ruin, scientists discover a gateway which offers instant transportation to an planet.
The Observed World: The gateway leads to a planet. The planet is in a planetary system that has a star. 42 planets rotate around it. The planetary system doesn't have any other celestial object. Besides the planetary system, there are other stars that form constellations.
The Actual World: The planetary system is actually inside an artificially constructed hollow sphere. The solid part of the sphere is of made of 2-Methyl-1,3,5-trinitrobenzene. Its hollow part is a sphere that is concentric with the hollow sphere. It produces no gravity in its hollow part. But it is thick enough that things outside it can feel gravity.
On the discontinuity between the solid and hollow part, there is a screen that displays the stars. The resolution of the screen is high enough, the paths of the stars and light are simulated well enough.
The hallow part of the sphere is large enough. No planet will hit the inside of the sphere.
Question: If a team of scientists are sent through the gateway with the purpose of investigating the planetary system, how would they realize that they are inside a hollow sphere?
Particularly, what would stand out to someone with a good grasp of physics, or astrophysics, even if they had no reason to suspect that they are in a hollow sphere?
Going out of the planetary system is not in their plan.
I'm not looking for a mathematical proof, but rather something that visibly stands out and would make a scientist decide to perform such a proof in the first place.
Their available technology is modern-day: spaceships, space shuttles, space stations, telescopes, etc.