Yes. Summer is a noun.
Direct objects are always nouns or pronouns.
I think you're confused about the 8 parts of speech (noun, pronoun, adjective, adverb, verb, preposition, conjunction, interjection) and parts of a sentence (subject, verb, direct object, etc.)
You can get explanations about the parts of speech (noun, pronoun, etc.) and the parts of sentences (subject, verb, etc.) by using the list at the left.
And here ... in the Terms section.
And here ...