I have three questions. 1. Why are galaxies disk shaped and not spherical? 2. Theoretically speaking, if there were a hollow sphere at the exact center of the Earth and you were in it then what would you feel from a gravitational point of view? Would you hover and be able to bounce from wall to wall of the sphere as if in zero G as you were pulled in all directions by gravity? 3. A: I saw a documentary about the Sun recently. It said that the sun uses five milion tons of hydrogen per second. I think it converts it in fusion with soemthing else and exess energy is given off. How much space would that amount take up. A swimming pool, a small lake? B: The sun is a delicate balance between the force of gravity crushing inward and the force of the fusion raction blasting outward. How does this fusion force work. Is it like a hydrogen bomb. That's splitting the hydrogenatom isn't it? But fusion just gives off excess energy. Does it radiate out as a shock wave or is it just heat/light. C: What substance is between the surface of the sun and the core which is super dense? I guess it's more hydrogen, is that stuff just wating its turn to be sucked in so it can too be fused for the reaction? D: I used to simplistically think of the sun as a massive globule of flamable liquid floating in space with only the surface burning like when they set fire to a liquer drink in a restraunt. I thought that the sun was so huge that it took billions of years to burn off just as it can take a long time for an iceberg to melt if it was towed to a hot area. If the heat and power of the sun comes to us from its core then why is the surface on fire? What is burning, is hydrogen flamable and if so why doesnt the whole lot go up.