Question: once in a blue moon origin of phrase
[{'answer': 'rarity of a blue moon', 'provenance': [{'wikipedia_id': '316038', 'title': 'Blue moon', 'start_paragraph_id': 5, 'start_character': 13, 'end_paragraph_id': 5, 'end_character': 34, 'bleu_score': 1.0, 'section': 'Section::::Definition.\n'}]}, {'provenance': [{'wikipedia_id': '316038', 'title': 'Blue moon', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 137, 'bleu_score': 0.9321022168949711, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9648550363134548304}, 'section': 'Section::::Definition.\n'}]}]