Kruskal and Penrose diagrams for a Minkosky spacetime

[JeffOCA]

Hello

I'm looking for diagrams (Kruskal and Penrose diagrams) representing Minkosky spacetime.
I found two diagrams at http://nrumiano.free.fr/Estars/int_bh.html (the two first diagrams of the page). Do they represent a Minkowski spacetime ?

Thanks,
Jeff

 

[PeterDonis]

The first diagram looks OK, but I haven't heard the term "Kruskal diagram" used to describe such a diagram of Minkowski spacetime; I've only heard "Kruskal diagram" used to describe a diagram using Kruskal coordinates for black holes (which looks somewhat similar).

The second diagram looks similar to the one on the http://en.wikipedia.org/wiki/Penrose_diagram" . The latter form makes more sense to me since, as I understand it, Penrose diagrams are supposed to represent a "spherical" sort of coordinate system, where the spacelike dimension is radius r. In this interpretation having a left half of the diagram would correspond to a negative radius, which doesn't make sense.