30. IE •• The Sun’s mass is 1.989 × 1030 kg and it radiates at a rate of 3.827 × 1023 kW.

(a) Over time, must the mass of the Sun (1) increase, (2) remain the same, or

(3) decrease?

(b) Estimate the lifetime of the Sun from this data, assuming it converts all its mass into energy.

(c) The actual lifetime of the Sun is predicted to be much less than the answer to part (b), even though its energy emission rate will remain approximately constant. What does this tell you about the 100%
conversion assumption?

(d) Theoretical calculations predict the Sun’s lifetime (in its current stage) to be about 5 billion years. During that time, what percentage of its mass will be lost?