地球

1. Origins, structure, and basic meaning

• Structure: 地球, read ちきゅう, names Earth, the planet we live on.
• Basic usage: In 宇宙船から見た地球は、青く輝いていた。, Earth seen from the spacecraft was shining blue.

2. Common pitfalls and similar expressions

• Compared with 世界
  • 地球 focuses on the planet itself; 世界 can refer to countries and human society. The planet viewed from the spacecraft is 地球.
• Long sound
  • ちきゅう ends with a long きゅう. The small ゅ and following う are part of that sound; the reading is not ちきゆ.