When I was little, it was always "your AN-us"... but I remember very clearly that people started calling it "YOUR-uh-ness" from 1977, when the two Voyager spacecraft were launched (Voyager 2 visited Uranus in 1986). The general perception at the time was that TV presenters felt uncomfortable saying 'anus' out loud so they used a different pronunciation :p Ever since then, I've heard the latter pronunciation much more often in the media, but I've always thought of it with the former pronunciation because that's the one I learned first!

(Facts that may or not be relevant: I was born in 1964 and have always lived in the UK. Also, I've always been obsessed with astronomy (the first known photo of me is as a toddler looking at a newspaper photo of the moon!), and I was a member of an astronomical society as a teenager and went on to study astronomy at university.)