Astrophysics Question – quite simple?
2.a The Sun’s surface temp measured 5700k . Calculate peak wavelength – I got 5.1X10^-7m
b. The peak wavelength from the sun is in fat measured on Earth as being 470nm . Why is the measured value different from your calculated value ?
For the above question I was thinking something to do with absorption by the atmosphere of different colored light would cause the change in values.
Second , for graphs which shows the distribution of power emitted over different wavelengths . Stars with higher temperatures will have more of their energy in the visible spectrum , while ones with lower temperatures will have less energy in this . Is this the correct reason why a star with say 11000k temp would appear blueish ? Or is there something else to consider .
Hopefully this is clear , thanks for any help .
Simple in terms of complex calculations .
a) Wien’s displacement law: L (nm) = 2.9 x 10^6 nm·K/ T (K)
Using your number of T=5,700 K I find: 510 nm like you.
Using the effective black body temperature of T=5,780 K this becomes 500 nm.
But as can be seen here, the Sun is not a perfect black body: http://en.wikipedia.org/wiki/File:EffectiveTemperature_300dpi_e.png
Absorption by the atmosphere is *not* the correct answer, as can be seen here: http://en.wikipedia.org/wiki/File:MODIS_ATM_solar_irradiance.jpg It leaves the peak at the same place.
2) Wien’s displacement law again: L (nm) = 2.9 x 10^6 nm·K/ 11,000 K = 263 nm So the peak clearly lies in the ultra-violet. But as this is outside the visible spectrum, we observe the peak as blue, the closest visible colour. Or more technically: it’s the star’s spectrum multiplied by the observation function of our eye, which is zero outside the visible.
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