Astronomy Fundamentals

Matter and Energy

What is energy?

Energy is that which makes things happen in the universe. It is that which is exchanged between any two particles in order for those particles to change—their motion, their properties, or anything else—in any way. Energy is everywhere around us; it takes so many different forms that it is hard to pin down. Heat is energy; light is energy; everything that moves carries kinetic energy. Even matter itself can be converted into energy, and vice versa.

