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Magnitude of Stars The magnitude $M$ of a star is a measure of how bright a star appears to the human eye. It is defined by\[M=-2.5 \log \left(\frac{B}{B_{0}}\right)\]where $B$ is the actual brightness of the star and $B_{0}$ is a constant.(a) Expand the right-hand side of the equation.(b) Use part (a) to show that the brighter a star, the less its magnitude.(c) Betelgeuse is about 100 times brighter than Albiero. Use part (a) to show that Betelgeuse is 5 magnitudes less bright than Albiero.
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5 \log \left(\frac{B}{B_{0}}\right)$. We can use the property of logarithms that $\log(a/b) = \log a - \log b$ to rewrite the right-hand side of the equation. Show more…
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The magnitude M of a star is a measure of how bright a star appears to the human eye. It is defined by M = -2.5 log(B/B0) where B is the actual brightness of the star and B0 is a constant. (a) Expand the right-hand side of the equation. (b) Use part (a) to show that the brighter a star, the less its magnitude. Suppose B1 and B2 are the brightness of two stars such that B1 < B2, and let M1 and M2 be their respective magnitudes. Since log is an increasing function, we have log(B1) ? log(B2) log(B1) - log(B0) ? log(B2) - log(B0) log(B1/B0) ? log(B2/B0) -2.5 log(B1/B0) ? -2.5 log(B2/B0) M1 ? M2 Thus, the brighter star has less magnitude.
The brightness of stars is expressed in terms of magnitudes on a numerical scale that increases as the brightness decreases. The magnitude $m$ is given by the formula $$ m=6-2.5 \log \frac{L}{L_{0}} $$ where $L$ is the light flux of the star and $L_{0}$ is the light flux of the dimmest stars visible to the naked cyc. (A) What is the magnitude of the dimmest stars visible to the naked eye? (B) How many times brighter is a star of magnitude 1 than a star of magnitude $6 ?$
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