One of the absorption lines of hydrogen has a rest wavelength of 656 nm (at rest means with respect to the observer, like in a lab). You observe several stars and measure the wavelength of this same hydrogen absorption line in each star. Based on the measured wavelength of this line, which star is moving towards the Earth the fastest?
A) 640 nm
B) 670 nm
C) 656 nm
D) 630 nm
E) 680 nm

Question

Quizplus · Accepted Answer

The wavelength of the hydrogen absorption line gives us information about the speed of the object relative to us. A shorter wavelength (blueshift) indicates that the object is moving towards us, while a longer wavelength (redshift) indicates that the object is moving away from us.

Based on the given wavelength values, we can see that option D has the shortest wavelength (630 nm) compared to the rest wavelength of hydrogen (656 nm). This indicates that this star is moving towards us the fastest, making it the correct answer.

One of the Absorption Lines of Hydrogen Has a Rest