Flat-Earthers like to mention an astronomical event or a specific celestial geometry and insist it cannot possibly occur if Earth is a rotating sphere orbiting the sun. They would incorrectly proclaim it as “evidence” of a flat, stationary Earth.
We can ask them the time of the event and the observer’s location, then use Stellarium or a similar app to simulate the event. If it produces the same result as the actual observation, then they have nothing to complain about. And the problem was just caused by their failure to understand and to create the correct model.
Stellarium is a planetarium software. It can render a realistic projection of the sky in real-time and any time in the past or the future, with relatively good accuracy. Stellarium is free software and costs nothing to download. It is freely available for all the major desktop operating systems. In addition, there is a version for mobile phones/tablets, albeit a paid one, and a simpler web-based version.
Stellarium uses the spherical Earth model. If the result produced by Stellarium matches the actual observation, then there is nothing wrong with the spherical Earth model. We can use the app to tell us if it is just an error in the model or an actual discrepancy between observation and expectation. The latter will be much rarer.
Stellarium Using Flat Earth Claim
Some flat-Earthers claim that Stellarium is made using the flat Earth model. However, we can easily prove this wrong by using Stellarium to simulate how the Earth appears from the surface of the Moon:
- Find the Moon: Ctrl-F, type “moon”, Enter
- Move observer to the selected object (Moon): Ctrl-G
- Find the Earth: Ctrl-F, type “earth”, Enter
- Turn off horizon if the Earth is below the horizon: G
- Zoom on to the selected object (Earth): /
If done correctly, Stellarium will show the spherical Earth in all its glory, as seen from the Moon.