Carl Sagan went my school in Brooklyn NY PS 101 in Bensonhurst Brooklyn when he was a child.
In (I think it was) 1979 I was in 6th grade, Carl Sagan came to our class as that was his 6th grade classroom. They taped a Cosmo episode in our class ( Episode The Backbone of Night) I remember my school principal was going crazy telling us to behave ourselves in a nice fashion as "Carl" was coming. I had no idea what or who he was talking about. All I remember that he was a nice man that brought us pictures of the moons and planets. Geesh, If I only knew then, what I know now, I would have been really excited about meeting him, but what does a 10 year old know

As far as the lectures go you can try www.smartflix.com they do have some lectures there that you can rent (its like netflix) they do have some interesting ones by Dr Neil Tyson, I love his Black Hole stories.

Let me know if you find the lectures