Yes, it is a bit hit and miss....the last couple of years it was too misty for the sun to light the chamber. Also because of a slight tilt in the axis of earth's rotation, slightly less light enters.
People tend to think that intelligence evolved over time, but this megalithic tomb was constructed using measurement. Amazing. And it took many years to construct.
I also found it fascinating that it is older than Stonehenge and the Giza pyramids.
Yes, you're right. People forget how ancient these monuments actually are. Our ancestors were a lot smarter than we tend to give them credit for.