To solve the equation \( a^2 = 26 \), we take the square root of both sides. This gives us:
\[ a = \pm \sqrt{26} \]
Thus, the solutions for \( a \) are:
\[ a = \sqrt{26} \quad \text{and} \quad a = -\sqrt{26} \]
The answer in simplest radical form is:
\[ a = \pm \sqrt{26} \]