To find angle $ \alpha $ use formula:
$$ \sin \left( \alpha \right) = \dfrac{ h }{ a } $$After substituting $ h = \frac{ 1 }{ 2 } $ and $ a = 1 $ we have:
$$ \sin \left( \alpha \right) = \dfrac{ \frac{ 1 }{ 2 } }{ 1 } $$ $$ \sin \left( \alpha \right) = \frac{ 1 }{ 2 } $$ $$ \alpha = \arcsin\left( \frac{ 1 }{ 2 } \right) $$ $$ \alpha = 30^o $$