1) The Hubble Space Telescope, launched in 1990, has provided breathtaking images of distant galaxies and deep space.

2) The Danube River, flowing through ten countries in Central and Eastern Europe, is the second-longest river in Europe. It has played a significant role in the cultural and economic development of the regions it traverses and is a popular waterway for river cruises.

3) The Southern Ocean surrounds Antarctica and is the coldest and least-visited ocean.

4) The novel "To Kill a Mockingbird" by Harper Lee has been translated into more than 40 languages and has sold over 40 million copies worldwide.