When a spectral line of wavelength `lambda = 0.59 mu m` is observed in the directions to the opposite edges of the solar disc along its equator, there is a difference in wavelengths equal to `delta lambda = 8.0pm`. Find the period of the sun's revolution about its own axis.

Explanation

One end of the solar disc is moving towards us while the other end is moving away form us. The angle `theta` between the direction in which the edges of the disc are moving and the line of observation is small `(cos theta~~1)`. Thus
`(Delta lambda)/(lambda) = (2omegaR)/(c)`
where `omega = (2pi)/(T)` is the angualr velocity of the sum. Thus
`omega = (c Delta lambda)/(2R lambda)`
So `T = (4piR lambda)/(c Delta lambda)`
putting the values `(R = 6.95 xx 10^(8) m)`
we get `T = 24.85` days