I came across this thing the other day and I've been wondering about it ever since. Curious if anyone else has come across this or know what it is.

I was heading to Markarth and I saw a pillar of light off of the road so I went to check it out. It was coming straight out of a dragon mound and looked a bit like the aurora borealis.

There were no dragons around and I waited around but no dragon came out. There was nothing that could be activated. I tried several different dragon shouts while standing in the light and deep mumbling voice that said something that sounded like: "You can speak but can you listen." Although even after hearing it several times I'm still not sure exactly what was being said.

Thanks to anyone who has info on this mystery.

That can happen if Alduin summoning the dragon is interrupted somehow. His summoning magic remains but the trigger for the dragon to emerge doesn't happen.

It's just a glitch.

It happened to me, too. It seems to be a bug. Was it near Dragon Bridge? Are you going through the main quest? Came across Alduin at the mound on my way to Sky Haven Temple, who did the whole resurrect sequence but nothing else happened. Interestingly, re-loading the game (saved there) and then travelling to Dragon Bridge appeared to have activated the dragon (when I returned to the mound it was empty).

As far as I know, all the dragons in mounds are named.

It also happened to me on my way to Rorikstead (I never travelled there after 100 hours of gameplay, so I thought "why not?"). I walked into the pillar of light and some named dragon started attacking me. I'd assume it's just some glitch.