= Color index
{title2=$B-V$}
{wiki}
= Colour index
{synonym}
A <colour index> is the difference of an object's measured <apparent magnitudes> in two <photometric passbands>, such as $B-V$. Since magnitude is logarithmic, this difference measures a flux ratio after the respective <magnitude zero points> are accounted for. It describes spectral shape rather than the object's overall brightness, and changes with both intrinsic radiation properties and <interstellar extinction>.
Back to article page
