\magnification=\magstep2


$$
   (m_1 - m_2) =  2.5 * \log_{10}{ {I_2} \over {I_1} }
$$

$$
   { {I_2}\over{I_1} } = 10^{0.4(m_1 - m_2)}
$$

$$
   (m - M) = 5 \log_{10}d - 5
$$

$$ 
   I_1 \neq 2 I_2
$$

$$ 
   I_1 \sim 10\thinspace I_2
$$




\bye