Star Shining Bright

Classical Mechanics Level pending

A cepheid variable star's brightness can be predicted by observing the period over which its luminosity varies.

A particular cepheid variable is found by this method to have a luminosity of 4 × 1 0 31 W 4\times 10 ^ {31} \text{ W} . The intensity of its light on Earth is 0.00025 W/m 2 0.00025 \text{ W/m}^2 . How far away is the star in metres?

1 0 17 10^{17} 1 0 18 10^{18} 1 0 16 10^{16} 1 0 19 10^{19}

Andrew Normand by Andrew Normand , 31, United Kingdom

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1 solution

Andrew Normand
Jan 29, 2017

Use the equation for luminosity and radiation intensity:

I = 1 4 π r 2 I = \frac{1}{4\pi r^2}

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