Grammarians say tense is time in language . In English , we have two tense forms : past and present. For teaching purposes, some teachers tell their students that there are three tenses: past , present and future. However, this is not really true. Anyway, Aspect is defined as " how the action happened" or " how the speaker/writer describes the action : simple , progressive (continuous) , perfect and progressive.
e.g.
I wrote a letter . The tense here is past.The aspect is simple .It indicates an action which happened in the past and finished.
I was writing a letter . Tense is past . Aspect is continuous. It shows that the action was continuous when I reported the action .
As for the poem , I think there two tenses : past and present and the aspect is simple but you have active and passive voice forms in some verb phrases. Past tense verbs show the poet's experience about the world . Whereas, the present show the facts about our world.