5. The answer to the previous question implies that there might be a relationship between the color index of a star and its main-sequence lifetime. What is that possible relationship

What would the difference of spectral lines emitted by hydrogen gas in distant galaxies which is normally found at a wavelength of 21 cm on earth, be observed at 21.1 centimeters?

True or false: the revolution of the earth creates day and night as it rotates around the sun

Does anyone know how to solve this problem? i really need . i made an attempt but i just cant get it. a metal rod is 25.000 cm long at 25.0 degrees celsius. when heated to 102.0 degrees celsius, it is 25.054 cm long. what is the coefficient of linear expansion for this metal.