1) Serena Williams is an American professional tennis player widely regarded as one of the greatest athletes in the sport. She has won numerous Grand Slam titles and Olympic gold medals and has become an influential figure both on and off the tennis court.

2) In Norse mythology, the Valkyries are divine maidens who serve Odin, the chief god. They are responsible for selecting warriors worthy of entering Valhalla and escorting them to the afterlife. They are often depicted as powerful and beautiful figures, riding winged horses and wielding spears.

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

4) The first successful consumer digital camera, the Apple QuickTake 100, was released in 1994 and had a resolution of 640 x 480 pixels.