Помогите правильно расставить артикль.1) ___ Earth is ___ planet.2) ___ Sun

Помогите правильно расставить артикль.
1) ___ Earth is ___ planet.
2) ___ Sun is ___ star.
3) ___ Earth moves around ___ Sun.
4) ___ galaxy is ___ large group of stars.
5) People started to travel to ___ space in the 20th century.
6) There are thousands of millions of stars in ___ Galaxy.