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By Wien's law, the peak emission wavelength is inversely proportional to a body's absolute temperature. Stars A and B have surface temperatures 3000 K and 6000 K, are at the same distance from Earth, and have equal radii. Which statement about their emitted radiation is correct?

1. Both A and B look equally bright in the visible.
2. A looks brighter than B in the infrared.
3. B looks brighter than A in the infrared.
4. A emits more in the visible range than in the infrared.

Correct answer: A looks brighter than B in the infrared.

Solution

Star A at 3000 K peaks in the infrared (lambda_max ~ 966 nm), so it is the brighter of the two in the infrared region, while the hotter star B peaks toward the visible.

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