Most scientists say a star can never become a planet, but the boundaries between these stellar objects can sometimes be murky.
Cities like Lahore, Pakistan, Hotan China and Delhi, India have consistently poor air quality, but it's impossible to accurately identify the city with the world's worst air pollution.
Photos show what looks like a line between the Atlantic and Pacific with different water colors on either side, but is there some kind of barrier or do the two oceans mix?
The Greek writer Plutarch proposed this question: If a ship's planks are replaced over time due to wear and tear until none of the original pieces remain, is it still the same ship?
Artificial lights can be deadly to the insects that fly around them, so why do these critters do it?
Cats may purr because they're happy, but also for a slew of other reasons, including getting their owner's attention and stress.
Coal takes tens if not hundreds of millions of years to form; it all starts with living plants that eventually fossilize.
Pangaea was one of the largest continents in world history, but now it's broken up. So which continent today is the largest, and which is the smallest?