I think as we pretend to go to space, everyone shoould get at least a basic knowledge of orbital mechanics or something like that.

I thought of making somekind of PDF or powerpoint explaining the basics of the topic. Other way to go would be giving lectures for limited people (say 50 for example) repeating every 2 weeks in skype or something like that . All that would be with less math as possible so all the people could understand.

Other topics to cover may be geology, astronomy, biology,...

You should consider knowledge repository formats and move away from fixed things like the PDF format. PowerPoint is intended to be proprietary, also no good idea. Go HTML5 and build markup for a slide: https://www.polymer-project.org/1.0/

.pdf, powerpoint(eww) - these are accessible for multiple, in their own time, so not an overly poor choice, although as nihylum mentions, you should attempt to avoid using proprietry formats where possible.

For a "lecture" why not record video footage? it can reach a wider audience over a longer period of time. A fortnightly "Q&A" session could cover people's questions(tho if this was archived, over time it could answer people's questions, too).

As to a medium to conduct this, I'm sure you could come up with a better solution than one that would require participants to trash local security. Skype, or anything like it - a set of spyware tools and server side exploits - is definitely something worth avoiding.

Of course it wouldn't be with any propietary formats, but just for people to get and idea of what I'm trying to say. Also I like the idea of doing videos in youtube instead of live lectures but doing some Q&A in some way, e-mail, live Q&A and things like that.

If we try to universalize the knowledge we have to start somewhere.

have you tried collaborating as a teacher with https://www.khanacademy.org/