The illusion that the sun goes round the earth 是个同位语从句吗?

问题描述:

The illusion that the sun goes round the earth 是个同位语从句吗?
为什么不是The illusion is that the sun goes round the earth?或者
It is the illusion that the sun goes round the earth?那不又是表语从句了?很混乱,

你给的这句话是同位语从句,但不完全.