<P> The Sun is roughly middle - aged ; it has not changed dramatically for more than four billion years , and will remain fairly stable for more than another five billion years . It currently fuzes about 600 million tons of hydrogen into helium every second , converting 4 million tons of matter into energy every second as a result . This energy , which can take between 10,000 and 170,000 years to escape from its core , is the source of the Sun 's light and heat . In about 5 billion years , when hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydrostatic equilibrium , the core of the Sun will experience a marked increase in density and temperature while its outer layers expand to eventually become a red giant . It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus , and render Earth uninhabitable . After this , it will shed its outer layers and become a dense type of cooling star known as a white dwarf , which no longer produces energy by fusion , but still glows and gives off heat from its previous fusion . </P>
<P> The Sun is roughly middle - aged ; it has not changed dramatically for more than four billion years , and will remain fairly stable for more than another five billion years . It currently fuzes about 600 million tons of hydrogen into helium every second , converting 4 million tons of matter into energy every second as a result . This energy , which can take between 10,000 and 170,000 years to escape from its core , is the source of the Sun 's light and heat . In about 5 billion years , when hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydrostatic equilibrium , the core of the Sun will experience a marked increase in density and temperature while its outer layers expand to eventually become a red giant . It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus , and render Earth uninhabitable . After this , it will shed its outer layers and become a dense type of cooling star known as a white dwarf , which no longer produces energy by fusion , but still glows and gives off heat from its previous fusion . </P>
where does the sun 's luminosity come from
where does the sun 's luminosity come from
, converting 4 million tons of matter into energy
, converting 4 million tons of matter into energy