There is a great deal of material on the internet, on astronomy and on physics (and on any other subject under the sun).

Unfortunately, there is no certain way to tell by looking at any particular material you might come across whether it is crackpot material, illucid, fringe science, pseudo-science, good science, or anything in between.

You can find several 'crackpot' detectors online - webpages that give a few, quick guidelines (lack of math, equations, numbers; lack of references to papers published in relevant peer-reviewed journals; invoking Galileo; and so on) - and they are often quite good at making a first cut.

The case of Marmet: the material is most certainly ATM (Against The Mainstream).