How many famous explorers are mentioned in this passage? Who are they?

Through history there have been many great explorers. Have you, for example, heard of Mar co Polo, the famous Italian traveller? He was one of the first Europeans to travel to China. He arrived in China in the late 13th century. About 200 years later Christopher Columbus sailed from Spain by ship. He was looking for a new way to reach India. However, as you probably know, he did not reach India. He landed in America. Five hundred years after Columbus, in the 1930s, a famous explorer named Richard Byrd was one of the first persons to fly over both the North and the South Poles.
     Today we continue to explore this world, and are starting to explore other worlds, too. In the late 1950s and the 1960s Russian and American scientists sent many unmanned spacecrafts to the moon. These spacecrafts sent back valuable information about the moon. Then on July 16,1969, the first manned spaceship to the moon left earth. On that day Apollo 11 blasted off with three American astronauts on board. Four days after blast-off, two of the astronauts landed on the moon. They then explored the surface of the moon. About two days after landing on the moon, they started back to earth. They arrived safely back to earth a few days later.
     Today we are sending unmanned spacecrafts to other planets. In the future we might walk in Mars or Venus the way we did on the moon. We might even travel to other galaxies! Who knows? One thing we know for sure is that we will continue to explore this world and other worlds, too.