The BBC released the first official full trailer for the Doctor Who 50th anniversary special, The Day of the Doctor, and the show's notoriously meticulous fans are parsing through what little footage they have to figure out what they can learn about the new changes. The BBC let the trailer loose on the Internet Friday evening, and sent Doctor Who fans into a tizzy in the process: 

There's more than enough packed into this forty second spot for Who fans to endlessly analyze. We see David Tennant, the Tenth Doctor, and Matt Smith, the Eleventh Doctor, together for the first time in the trailer. (That ringing sounds is fan girls and boys screaming because, oh. em. gee.) John Hurt appears as the Lost Doctor, and the special is supposed to fill in a lot of his backstory. Big red crystal buttons are prominently involved. It should be fun. 

For those clued in to the Doctor Who universe, there are intense discussions happening on fan boards that read like Russian if you're not in the know. The U.K. newspaper Metro has theories about possible callbacks and cameos that Doctor Who diehards may recognize: 

There’s plenty of action which echoes previous Who stories. As at the beginning of his debut episode, The Eleventh Doctor, we see Matt Smith dangling from the TARDIS above London. The Tenth Doctor rides a white horse through the TARDIS doors, reminiscent of The Girl in the Fireplace. And there has clearly been a large investment in the effects budget, with visuals of a Dalek fleet, space battles and plenty of explosions

If this Doctor Who talk is getting you excited but you have no idea what any of it means, there's still plenty of time to watch most of the series (start with the reboot!) before the 50th anniversary special on November 23.

(Correction: An earlier version of this post said the Twelfth Doctor, played by Peter Capaldi, would debut in the 50th anniversary special. In fact, Capaldi makes his debut during the Christmas special. Sorry for any confusion.)