大象传媒

The Sun

The Solar System was formed around 4.6 billion years ago from a large cloud of dust and gas, called a . This collapsed under its own gravity, transferring to in its particles. As the nebula collapsed it became denser, and rotated more rapidly. Collisions between particles caused kinetic energy to be transferred as and . The core of the nebula began to form a hot, dense .

Brian Cox explains how the Earth was formed

When the Sun鈥檚 core became hot enough and dense enough, reactions began. In these reactions:

  • hydrogen join together to form helium nuclei
  • energy is transferred by radiation

A star like the Sun is at equilibrium - gravity tends to pull it inwards, and radiation pressure from the nuclear reactions tends to expand it outwards. In other words, the gravitational collapse is balanced by the expansion due to fusion energy.