>>our sun is of the correct size to turn into a red giant and will one day expand until the earth is inside the sun - and the earth will end. ---------
Where did you get that nonsense from? Christians KNOW the world will NEVER end.....world without end. Amen.<<
One of the limitations of the Internet is that its sometimes hard to tell the tone of the poster... I can't tell if you being ironic or straight forward or something else...
But basically a star converts hydrogen to helium, light and other radiation. As a star below a certain mass runs short of hydrogen the star collapses and compresses so much that it can start to burn helium into carbon. The tremendous energy released causes the star to expand.
In the case of our sun, the scientific consensus is that it has about 5 billion years worth of hydrogen left but after that time it will expand to a radius larger than the distance to the earth. The earth will be inside the sun and the earth will end.
Before the earth ends, there will be enough time to repeat recorded human history 625,000 times.