Adolescence /ˌæd

earth /ɜːθ/ /ɝːθ/ noun PLANET
1. [ S or U ] ( usually Earth ) the planet third in order of distance from the Sun, between Venus and Mars ; the world on which we live
The Earth takes approximately 365 1 4 days to go round the Sun.
The Circus has been described as the greatest show on Earth (= in the world) .
exploration /ˌek.spləˈreɪ.ʃ ə n/ /-splɚˈreɪ-/ noun [ C or U ]
when you search and find out about something
Livingstone was the first European to make an exploration of the Zambezi river (= to travel to it in order to discover more about it) .
We need to carry out a full exploration (= examination) of all the alternatives.
The exploration (= search) for new sources of energy is vital for the future of our planet.
explorer /ɪkˈsplɔː.rə r / /-rɚ/ noun [ C ]
someone who travels to places where no one has ever been in order to find out what is there
Magellan was a famous sixteenth-century explorer.
galaxy /ˈgæl.ək.si/ noun
1. [ C ] one of the independent groups of stars in the universe
2. [ C ] a meeting of rich and famous people
Present tonight at the long-awaited opening of this film are a whole galaxy of stars from the acting and musical professions.
3. the Galaxy ( also the Milky Way )
the very large group of stars that contains the solar system (= the sun and all the planets, including Earth, that go round it)