Shockwaves are abundant in astrophysics, from gamma ray bursts, to supernovae to planetary collisions.
In many cases such shocks emerge from the edge of the system, be it the surface of the planet or the edge of the star.
We discuss the physics of such shocks. Interesting hydrodynamics solutions allowing acceleration of shocks as they propagate
towards the edge, as well as deviation from equilibrium as the dynamical and diffusion timescales become short and photons
leak out of the systems. We also present new solutions for breakout of oblique shockwaves. These processes determine the first
signals we see from a supernovae or from the electromagnetic counterpart of gravitational wave sources such as neutron star mergers.
This dynamics will also set the amount of atmosphere ejected from planets in the process of their formation.