Doppler shift principle
Hiya, I have to hand in this assignment tomorrow but I'm stuck on a Doppler shift question, I genuinely need some help.Here it is:The spectrum of the galaxy is taken. The Ha line (atomic energy given off by Hydrogen) is 656.3nm yet it is observed at 661.5nm. Calculate the recessive speed of this galaxy using the Doppler shift principle:v=c*(delta*lambda)/lambda
Original post by M.Markland
Hiya, I have to hand in this assignment tomorrow but I'm stuck on a Doppler shift question, I genuinely need some help.Here it is:The spectrum of the galaxy is taken. The Ha line (atomic energy given off by Hydrogen) is 656.3nm yet it is observed at 661.5nm. Calculate the recessive speed of this galaxy using the Doppler shift principle:v=c*(delta*lambda)/lambda
So where did you get stuck?
fwiw delta lambda (Δλ... upper case delta, lower case lambda) just means 'difference in lambda'... the delta is not some new mystery variable that's popped up out of nowhere.
Im aware of that, im confused on replacing the variables, and what the outcome is supposed to represent
Δλ=λobserved-λ0
Δλ/λ0 has length units top and bottom of the fraction, so it's dimensionless... as long as you use a consistent unit you don't need to convert to SI
fwiw Δλ/λ0 is sometimes called z - e.g. you'll see literature talking about high z galaxies... which just means high redshift galaxies.
so in this case Δλ = 661.5-656.3 nm
=5.2 nm
and z=5.2/656.3
= 7.92x10-3
so the speed at which the galaxy is receding is 7.92x10-3 c
if you want the speed in SI units use the SI value of c from a databook
(7.92x10-3) 3.00x108
=2.38x106 m/s
Δλ/λ0 has length units top and bottom of the fraction, so it's dimensionless... as long as you use a consistent unit you don't need to convert to SI
fwiw Δλ/λ0 is sometimes called z - e.g. you'll see literature talking about high z galaxies... which just means high redshift galaxies.
so in this case Δλ = 661.5-656.3 nm
=5.2 nm
and z=5.2/656.3
= 7.92x10-3
so the speed at which the galaxy is receding is 7.92x10-3 c
if you want the speed in SI units use the SI value of c from a databook
(7.92x10-3) 3.00x108
=2.38x106 m/s
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