Within the Sun's core, immense pressure and the rapid motion of hydrogen atoms cause collisions that fuse hydrogen into helium. The helium and a stray neutron weigh slightly less than the hydrogen that created them, and the missing mass is converted into energy according to Einstein's E=mc2 formula, producing thermonuclear heat. Every second, the Sun converts 4 million tons of mass into energy, generating 386 billion billion million watts of power. About every 11 years, the Sun undergoes increased surface activity, including solar wind, sunspots, storms, and flares, which send high-energy particles and radiation through the solar system and can affect Earth by causing surges in power lines, disabling satellite communications, exposing airline passengers to harmful x-rays, and threatening astronauts on the moon. This bombardment also produces the Northern Lights when solar particles are trapped in Earth's magnetic field and collide with oxygen and nitrogen in the atmosphere, releasing colored light, and a sun quake can spread across the solar surface after a flare. The Sun is a star formed from a giant cloud of hydrogen atoms from the Big Bang that collapsed under gravity until nuclear fusion began. It has spent perhaps 4.5 billion years as an active nuclear furnace, has used half of its hydrogen fuel, and has about 5 billion years left. Over the next 1 billion years, it will brighten by about 10 percent, after which Earth's oceans will boil away and life will become very difficult. At the end of its life, hydrogen in the Sun will be exhausted, helium in the core will begin to fuse during the red giant phase, and the outer surface will cool and expand to 150 times its current size, incinerating all the planets in the Solar System. When the helium fuel is exhausted, fusion will cease, gravity will collapse the star to about the size of Earth, and the dead, cooling core will remain as a white dwarf.