Bohr Radius

$a_0=\frac{4\pi {\epsilon }_0{\hslash }^2}{m_e{e}^2}\approx 0.529\stackrel{\text{lower}.5em\circ }{\mathrm{A}}$

• $\stackrel{\text{lower}.5em\circ }{\mathrm{A}}$ is the Angstrom