<Tr> <Th> Unit of </Th> <Td> length </Td> </Tr> <Tr> <Th> Symbol </Th> <Td> a or r </Td> </Tr> <Tr> <Th> Named after </Th> <Td> Niels Bohr </Td> </Tr> <Tr> <Th_colspan="2"> Unit conversions </Th> </Tr>

In the equation for the orbital radius in hydrogen-like atoms a0 is called the