SkipCaptcha
1,279
edits
Changes
Jump to navigation
Jump to search
Line 8:
Line 8: − + − + + + + + + + + +
Expand definitions of apparent and absolute magnitudes
With Galileo and the telescope, it was possible to make out stars that were much dimmer than sixth magnitude.
With Galileo and the telescope, it was possible to make out stars that were much dimmer than sixth magnitude.
== Today ==
== Modern definition ==
In the 1800s, Norman R. Pogson proposed and codified magnitude to be a logarithmic scale where the difference between the first and fifth magnitude is one hundred times brighter. The ratio of one number to the next is the fifth root of one hundred, or about 2.512 - known as the Pogson ratio.<ref>http://www.astro.ufl.edu/~guzman/ast4402/lectures/lect06.html</ref>
In the 1800s, Norman R. Pogson proposed and codified magnitude to be a logarithmic scale where the difference between the first and fifth magnitude is one hundred times brighter. The ratio of one number to the next is the fifth root of one hundred, or about 2.512 - known as the Pogson ratio.<ref name=britannica/> For example, this means a magnitude +5.0 star is about 2.512 times brighter than a magnitude 6.0 star.
The apparent magnitude of a star, ''m''<sub>*M/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>
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]].
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>
:<math>M = m - 5 \log_10 \frac{d}{10}</math>
where ''m'' is the apparent magnitude and ''d'' is the distance to the object from Earth.
== Examples ==
== Examples ==