Question

Try out some of the principles of light by comparing Polaris to the sun.

a. The intensity of sunlight at a satellite in earth orbit is 1360 W/m2. What is the magnitude of the electric and magnetic field ?

b. Astronomers estimate the distance to Polaris is 431 light years and its intrinsic luminosity (energy per second) is 2200 times that of the sun. Use proportional reasoning and your answer to part a to estimate the intensity and the magnitude of the electric field at the earth. You can give it in terms of A.U., factors of earth’s distance from our sun.

c. A planet in the “habitable zone” around Polaris should receive a light intensity similar to our planet. Again use proportional reasoning to estimate what distance might be a good one.

d. The color of a star depends on temperature of the outer regions of the star. The peak wavelength for polaris is 400 nm and for the sun is 500 nm. Another famous star, Betelgeuse, has its peak wavelength at 828 nm. What color light are these specific wavelengths, and what is the frequency of this light? Actually, we perceive the first two stars to be “white” and Betelgeuse to be distinctly “red”. Explain in your own words.

Answer 1

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