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→Modern definition
The apparent magnitude of a star, ''m''<sub>*</sub> can be computed using,<ref>{{cite web|url=http://astronomyonline.org/Science/Magnitude.asp#:~:text=A%20Magnitude%20is%20the%20measure,of%20Magnitude%3A%20apparent%20and%20absolute.|title=Formulas - Magnitudes|accessdate=July 28, 2020|publisher=astronomyonline.org}}</ref>
The apparent magnitude of a star, ''m''<sub>*</sub> can be computed using,<ref>{{cite web|url=http://astronomyonline.org/Science/Magnitude.asp#:~:text=A%20Magnitude%20is%20the%20measure,of%20Magnitude%3A%20apparent%20and%20absolute.|title=Formulas - Magnitudes|accessdate=July 28, 2020|publisher=astronomyonline.org}}</ref>
::<math>m_* - m_c = -2.5 \log_{10} \frac{b_*}{b_c}</math>
::<math>m_* - m_c = -2.5 \log_{10} \frac{b_*}{b_c}</math>
where ''m''<sub>c</sub> is the apparent magnitude of a comparison star and ''b''<sub>*</sub> and ''b''<sub>c</sub> are the brightness of the star and comparison star as seen on Earth. The <math>\log_{10}</math> refers to a base 10 [[logarithm]].
where ''m''<sub>c</sub> is the apparent magnitude of a comparison star and ''b''<sub>*</sub> and ''b''<sub>c</sub> are the brightness of the star and comparison star as seen on Earth. Historically, the star [[Vega]] was used as a comparison and defined to have an apparent magnitude of +0.0, though recent measurements have meant it is now +0.3 in order to be consistent with other stars.<ref name=space.com/> The <math>\log_{10}</math> refers to a base 10 [[logarithm]].
The apparent magnitude of an object depends not only on how much light the object emits, but also on how far away the object is. To compare the instrinsic brightness of objects, the absolute magnitude is often used. It is defined as the magnitude of an object as seen from 10 [[parsec]]s (32.6156 [[light year]]s). The absolute magnitude, ''M'', can be calculated using,<ref>{{cite web|url=https://astronomy.swin.edu.au/cosmos/A/Absolute+Magnitude|title=Absolute Magnitude|accessdate=July 28, 2020|publisher=astronomy.swin.edu.au}}</ref>
The apparent magnitude of an object depends not only on how much light the object emits, but also on how far away the object is. To compare the instrinsic brightness of objects, the absolute magnitude is often used. It is defined as the magnitude of an object as seen from 10 [[parsec]]s (32.6156 [[light year]]s). The absolute magnitude, ''M'', can be calculated using,<ref>{{cite web|url=https://astronomy.swin.edu.au/cosmos/A/Absolute+Magnitude|title=Absolute Magnitude|accessdate=July 28, 2020|publisher=astronomy.swin.edu.au}}</ref>