The perpendicular bisectors of the sides $AB$ and $CD$ of the rhombus $ABCD$ are drawn. It turned out that they divided the diagonal $AC$ into three equal parts. Find the altitude of the rhombus if $AB = 1$.
1. Let \( a \) be the horizontal distance from \( A \) to \( B \) and let \( b \) be the vertical distance from \( A \) to \( B \). Since \( AB = 1 \), by the Pythagorean Theorem, we have:
   \[
   a^2 + b^2 = 1
   \]

2. Let \( \theta \) be the angle \( \angle BAC = \angle DAC \) and let \( x \) be any of the three equal parts of the diagonal \( AC \). Since the perpendicular bisectors of \( AB \) and \( CD \) divide \( AC \) into three equal parts, we have:
   \[
   AC = 3x
   \]

3. Using the Law of Cosines on \( \triangle ABC \) or \( \triangle ADC \), we get:
   \[
   1^2 = 1^2 + (3x)^2 - 2 \cdot 1 \cdot 3x \cdot \cos \theta
   \]
   Simplifying, we have:
   \[
   1 = 1 + 9x^2 - 6x \cos \theta
   \]
   \[
   0 = 9x^2 - 6x \cos \theta
   \]
   Since \( x \neq 0 \), we can divide by \( x \):
   \[
   0 = 9x - 6 \cos \theta
   \]
   \[
   \cos \theta = \frac{3x}{2}
   \]

4. Given that \( \cos \theta = \frac{1}{2x} \), we equate the two expressions for \( \cos \theta \):
   \[
   \frac{3x}{2} = \frac{1}{2x}
   \]
   Multiplying both sides by \( 2x \):
   \[
   3x^2 = 1
   \]
   \[
   x^2 = \frac{1}{3}
   \]
   \[
   x = \frac{1}{\sqrt{3}}
   \]

5. Let \( E \) be a point outside of the rhombus such that \( BE = a \) and \( AE = b \). Then \( \triangle AEB \) is a right triangle, and we have:
   \[
   (3x)^2 = (1 + a)^2 + b^2
   \]
   Substituting \( x = \frac{1}{\sqrt{3}} \):
   \[
   \left(3 \cdot \frac{1}{\sqrt{3}}\right)^2 = (1 + a)^2 + b^2
   \]
   \[
   3 = (1 + a)^2 + b^2
   \]

6. Using \( a^2 + b^2 = 1 \), we substitute \( b^2 = 1 - a^2 \) into the equation:
   \[
   3 = (1 + a)^2 + (1 - a^2)
   \]
   \[
   3 = 1 + 2a + a^2 + 1 - a^2
   \]
   \[
   3 = 2 + 2a
   \]
   \[
   1 = 2a
   \]
   \[
   a = \frac{1}{2}
   \]

7. Substituting \( a = \frac{1}{2} \) back into \( a^2 + b^2 = 1 \):
   \[
   \left(\frac{1}{2}\right)^2 + b^2 = 1
   \]
   \[
   \frac{1}{4} + b^2 = 1
   \]
   \[
   b^2 = 1 - \frac{1}{4}
   \]
   \[
   b^2 = \frac{3}{4}
   \]
   \[
   b = \frac{\sqrt{3}}{2}
   \]

Since \( b \) is the altitude of the rhombus, the altitude is \( \frac{\sqrt{3}}{2} \).

The final answer is \( \boxed{\frac{\sqrt{3}}{2}} \).