How does the sun "burn" if there is no oxygen in space?

At first glance, an image of the sun may resemble a roaring fire. However when astronomers talk about the sun "burning" they are actually talking about a process called nuclear fusion. This process involves the forcing together of tiny hydrogen nuclei in the core. Nuclear fusion takes place in the core as nuclear fusion need high pressure and high temperatures, both of which are present in the sun's core.