So maybe Una's story is set before this colossal act of Divine meddling, and young Faramir CAN see Sirius on a warm Midsummer's evening. Of course, it's odd that no one in LotR makes even the slightest allusion to this recent cosmic upheaval (which occurred within the lifetimes of all the story's major characters), but then again, they WERE a bit preoccupied...

Maybe it all happened on that day when the Sun doesn't rise. Or, perhaps it happens later in the Fourth Age. If the upheaval was massive enough, it would also explain why we've never found any archaeological remains from Gondor and Arnor...


(Sorry, but the explanation that Tolkien probably wasn't aware of the effects of precession of the equinoxes is just TOO prosaic for me.)

Those kinds of explanation are never as much fun!