This is the 5232nd most frequent Korean word.
달이
"달이" means "moon" (subject marker used in context).
In this sentence, '달이' is the subject of the sentence and means 'the moon,' specifically referring to it as shining.
달이 밝게 빛나고 있어요.
The moon is shining brightly.
Here, '달이' is asking about the occurrence of the moon rising, serving as the subject in a question.
달이 언제 뜨나요?
When does the moon rise?
In this sentence, '달이' again means 'the moon' and is used as the subject in a statement describing its beauty.