The real reason why Sherlock doesn’t know the solar system
Headcanon: When Sherlock was younger, his aunt gave him a book of constellations.
He’d never bothered with astronomy, well not until he’d started playing pirates with Redbeard at least. After all, one needs the stars to map out a safe course on the high seas.
He’d thanked his aunt and clutched the book closely to his chest, bounding up into his room to peruse it further, knowing from the beginning that it was going to be special.