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[monmarfori]

Our sun is only 4.55 years old. in the future will increase and grow in size and to expand in the red giant phase. then cool to white dwarf and to black dwarf.
4.55 present sun, 5778 K, present.
5 expands big a little, earth evaporates at 5823 K, 1.1 billion years.
6 will be a subgiant, earth near hot at sun cooling bright, 3 billion years.
8 will be a red giant, 5 billion years. Mercury engulfed. Venus at 1.0 AU. Earth is at 1.7 AU (250,000,000 km) away from the red giant in 7.6 billion years
12 will be a white dwarf, A dozen billion years. Our sun reached the white dwarf, 17 billion years.
13 will be a black dwarf, A many billion years, will reach that type. at 43 billion years.

[atommo999]

yes the expansion is due to chemical fusion.
41H → 22H + 2e+ + 2νe (4.0 MeV + 1.0 MeV)
21H + 22H → 23He + 2γ (5.5 MeV)
23He → 4He + 21H (12.9 MeV)
thats the formula for the chemical fusion the elements of the sun go through before the outer layer drifts off into space.