Question: How did Sauron take the form of a fiery eye? Isn't he powerless without the ring?
Answer:Most of Sauron's power was poured into the One Ring, but not all of it. Sauron cannot take a true physical form until the ring is returned to him but he can still use his power to form the eye to keep watch over Middle Earth.
If by "true form" you mean the form he originally took when he was created, it is unlikely. Sauron was a good, just, and respected being prior to being corrupted and likely wouldn't have such an evil appearance in his original form. It is important to note, however that the Eye of Sauron takes on a much more physical form in Peter Jackson's film that it does in the books. In the books, the eye is a red light hovering over the tower that has the vague appearance of an eye. The films makes the eye look like an actual, literal eyeball that moves and seems to have a personality.
Answer: Most of Sauron's power was poured into the One Ring, but not all of it. Sauron cannot take a true physical form until the ring is returned to him but he can still use his power to form the eye to keep watch over Middle Earth.
BaconIsMyBFF
Is the eye actually his true form?
If by "true form" you mean the form he originally took when he was created, it is unlikely. Sauron was a good, just, and respected being prior to being corrupted and likely wouldn't have such an evil appearance in his original form. It is important to note, however that the Eye of Sauron takes on a much more physical form in Peter Jackson's film that it does in the books. In the books, the eye is a red light hovering over the tower that has the vague appearance of an eye. The films makes the eye look like an actual, literal eyeball that moves and seems to have a personality.
BaconIsMyBFF
I meant has the eye been his true form ever since he lost the ring?
Sort of, yes. Sauron's spirit existed in a non-corporeal form and eventually built enough strength to form the eye.
BaconIsMyBFF
No, his true form is seen at the beginning of the film.