Doctor Who: 20 Things You Didn’t Know About A Christmas Carol
13. It Aired On A Brand-New Channel
The first episode of Doctor Who to air in high definition was the 2009 Easter special Planet of the Dead, because everyone really needed to see Lee Evans' face in the clearest resolution possible.
However, that episode (and every subsequent HD broadcast) was shown on a channel just called BBC HD, which showed high-def content from all across the BBC.
BBC One HD, which is dedicated entirely to HD content from the Beeb's main channel, didn't launch until November 2010, just in time for A Christmas Carol to be the first Doctor Who episode to grace its airwaves.