The upper atmosphere of the earth where the sun, moon, stars, and clouds appear.
Gloss: STAR/\ CL:innumerable-in-sky(aah) [nod] MANY PLURAL-PRONOUN STUDY THEY FINISH TRY COUNT++ [neg] FAIL.
English equivalent: Many astronomers have tried to count the innumerable stars in the sky and have failed.
These glosses are rough. In this ASL sentence, there is a relative clause approximately as "those who study stars" that is referred to 'astronomers'.
In topicalization, STAR is the topic.