How can a ship 100 km in diameter cause any significant dimming of a star, which is 21,980,000 km in diameter? It would have to be pretty close to here and lined up just so perfectly.
Why even assume it's a spaceship and not an asteroid or a rogue planet?
The moon is smaller than the sun, and yet still we have eclipses. It's just a matter of perspective.
The object[s] would have to be lined up. That's why an artificial object intentionally traveling to Earth is in some sense more plausible than an asteroid, which could be headed in any direction.
Why even assume it's a spaceship and not an asteroid or a rogue planet?