On Earth, gravity determines how the flame burns. All the hot gases in the flame are much hotter (and less dense) than the surrounding air, so they move upward toward lower pressure. This is why fire typically spreads upward, and it’s also why flames are always “pointed” at the top.
In microgravity or zero gravity, such as an environment in outer space, convection no longer occurs, and the flame becomes spherical. This effect is demonstrated in the fire ball exhibit.