To find the value of the function \( y = \sin \theta \) when \( \theta = \frac{\pi}{3} \), we can use the known values of the sine function for common angles.
The sine of \( \frac{\pi}{3} \) (or 60 degrees) is:
\[ \sin\left(\frac{\pi}{3}\right) = \frac{\sqrt{3}}{2} \]
Thus, the response that corresponds to this value is:
\[ \text{Start Fraction Start Root 3 End Root over 2 End Fraction} \]
Therefore, the correct answer is \( \frac{\sqrt{3}}{2} \).