Final answer:
The phrase in question is an example of a metaphor, which is a direct comparison between two unlike things without using 'like' or 'as.'
Step-by-step explanation:
The phrase 'Shadows indicate riddles, illuminating unseen stars' is a metaphor. A metaphor is a figure of speech involving a direct comparison between two unlike things. Unlike a simile, which uses 'like' or 'as' to make a comparison, a metaphor states that one thing is another, to suggest a likeness between them. Here, 'shadows' do not literally illuminate 'unseen stars,' but rather, the metaphor describes how shadows, or perhaps the mysteries they represent, can reveal truths that are not immediately visible, akin to how stars might be revealed in a night sky once conditions allow.