No. Sun is a noun.
A noun doesn't describe something. That would be an adjective. An adjective of the sun is that its hot.
Sunny!
Bit hard to understand your question! Is this what you mean? What is an adjective in the sentence 'your sun is really a special star'? special is an adjective.
Sunny is an adjective, a word that describes a noun: a sunny day.
hot
Shining sun
Solar or sunny.
Solar
'Solar' , as in 'Solar System'.
Hot
adjective clause