1) The sitcom "Friends" is known for its iconic Central Perk coffee shop, where the main characters often gather.

2) The Atlantic Ocean is the second-largest ocean and is known for its strong ocean currents, including the Gulf Stream.

3) The Great Wall of China is not visible from space without aid, contrary to popular belief.

4) The smallest unit of time is known as a zeptosecond, which is equal to one trillionth of one billionth of a second.