Answer:
The italicized phrase is an appositive.
Explanation:
An appositive could be only a noun or a noun phrase that mentions the original noun by another name, it is right after the original noun in the sentence and it is surrounded by commas, in this case, "The moon" and "a yellow and full disc" are a noun and a noun phrase which are describing the same thing, and the second description is between commas.
