Question

A scientist is studying the light emitted by several celestial objects. He records the shifts in each object’s spectral lines (in nm). Based on these measurements, determine whether each object is moving toward or away from Earth. Use the diagram of the visible light spectrum to help you. 400 nm shifted to 430 nm 610 nm shifted to 580 nm 512 nm shifted to 480 nm 670 nm shifted to 690 nm

Answer 1

-- 400 nm shifted to 430 nm . . . longer than it should be; "red shifted"; moving away from Earth  

-- 610 nm shifted to 580 nm . . . shorter than at source; "blue shifted"; moving toward Earth

-- 512 nm shifted to 480 nm . . . shorter than at source; moving toward Earth

-- 670 nm shifted to 690 nm . . .longer than at source; moving away from Earth

Now I'd just like to ask one more itty bitty question, that you can think about while you're on this subject:  Astronomers really do this.  They measure how much the wavelength CHANGED, from the time it left the original source until the time they detect it. But HOW do they know what the wavelength WAS when it left the source ? ? ?

THIS is the part that blows my mind !