To find out how many joules of energy the Sun generates in a year, we can multiply the energy generated by the Sun per second by the number of seconds in a year.
Given:
- Energy generated by the Sun per second = \( 4 \times 10^{26} \) joules
- Number of seconds in a year = \( 3.15 \times 10^{67} \)
Now, we perform the multiplication:
\[ \text{Total energy in a year} = (4 \times 10^{26}) \times (3.15 \times 10^{67}) \]
We can multiply the coefficients and the powers of ten separately:
\[ = 4 \times 3.15 \times 10^{26 + 67} \]
Calculating the coefficients:
\[ 4 \times 3.15 = 12.6 \]
Now, we combine the powers of ten:
\[ 10^{26 + 67} = 10^{93} \]
So, we have:
\[ \text{Total energy in a year} = 12.6 \times 10^{93} \]
Next, we express \( 12.6 \) in scientific notation:
\[ 12.6 = 1.26 \times 10^{1} \]
Thus, we rewrite the expression:
\[ 12.6 \times 10^{93} = 1.26 \times 10^{1} \times 10^{93} = 1.26 \times 10^{94} \]
Therefore, the total amount of energy the Sun generates in a year, expressed in scientific notation, is:
\[ \boxed{1.26 \times 10^{94}} \text{ joules} \]