Chapter 33, Problem 13RQ

To determine

The time that the Sun will reach the red-giant stage.

Answer to Problem 13RQ

Sun will reach its red-giant stage, 500 million years from now.

Explanation of Solution

Continuous fusion happens in the Sun’s core between hydrogen and helium. From 500 billion years from now, that is in the old age, the hydrogen gets used up and gravity is more impactful than thermal pressure and Sun will pull inwards. The temperature will rise and the burned put hydrogen core contracts because of gravity.

Later, the fusion from helium to carbon will start. The helium carbon fusion will happen inside the Sun while the helium hydrogen fusion will occur outside the Sun in the shells. This causes the Sun to grow larger.

The much more intensity of nuclear fusion now increases the power of the thermal pressure and it will win over gravity. This will swell the Sun and the energy of the Sun will increase at a high rate. This is called the red-giant stage of Sun.

Conclusion:

Therefore, Sun will reach its red-giant stage, 500 million years from now.