Question

The human eye is most sensitive over the same wavelength range at which the Sun emits the greatest intensity of radiation. The Sun is a G-type star; see Table 17.1 in Section 17.2 for this classification scheme.

Suppose creatures were to evolve on a planet orbiting a star somewhat hotter than the Sun, let’s say an average F-type star. Let’s also assume that the atmospheric properties of their planet are the same as we find on earth today. To what wavelength ranges, approximately, do you think their vision would most likely be sensitive to? Explain your reasoning. For full credit, you should explore at least one resource besides your textbook. Be sure to cite references used.

Answer 1

To know the answer for this question, It is important to know why our eyes are sensitive to only visible spectrum of light.

In the Universe there are billions of stars. They are classified based on the spectral characteristics like temperature etc,. One of the type of classification is MK system.

Here these stars are classified under the alphabets like O, B, A, F, G, K and M. Here O is hottest star (above 30,000 K) and M is coolest star (2400 - 3700 K).

Our Sun is a G- type star with temperature around 5000 K to 6000 K. Though Sun is the black body emitting all frequencies, the major radiation it emits is the radiation corresponding to the effective temperature. The frequency range is calculated using Wien's displacement law ie,.

The range of frequency we obtained is visible range of electromagnetic spectrum.

The objects on the earth will majorly absorbs the visible radiation and emits in the same range. So majority of Living organisms have adapted themselves to have vision in this spectrum range. There are some organisms which are sensitive to the other wavelengths than visible. This is due to their life style and necessity for their survival.

Suppose there are creatures which evolved on a planet orbiting a star somewhat hotter than the Sun like F-type star, we have to know the effective temperature range of the star. For F- type star, effective temperature is around   6000 K to 7500 K. This temperature range comes under UV- Spectrum.

The objects in that planet absorbs the UV light from the star and emits majorly in that frequency. This makes the majority of creatures there to have vision sensitivity in the UV spectrum itself.

Hence the creature in the planet closer to F- type star will be more sensitive to UV radiation.