Why is the sky blue? Modern-day scientists know it’s because of the way the sun interacts with air molecules when sunlight enters the Earth’s atmosphere. In Leonardo da Vinci’s time, however, the answer wasn’t so clear. He questioned assumptions of the day, even those that seemed simple.

“It’s that type of always asking ‘Why?’ that led (da Vinci) to be the self-taught genius he is,” said Walter Isaacson, journalist and author. “An ordinary guy who sometimes procrastinated on his projects, but always loved the connection of beauty to nature to engineering and always asked the big why.”