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# Distance of a Galaxy - from redshift and bubbles constant watch

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1. I've been given a question and I've tried finding formulae online (as they aren't in my notes) and have come up with nothing that's actually a realistic answer:

"A spectral line of hydrogen (wavelength 21.1cm in the lab) emitted by a galaxy is oversee to have a wavelength of 21.4cm. If Hubble constant has a value of 0.06 metres per second per parsec, how far is this galaxy from Earth (in parsecs)? Given c=3x10^8."

Can anyone provide an insight into how to go about doing this question?

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2. (Original post by ThatTallGuy)
I've been given a question and I've tried finding formulae online (as they aren't in my notes) and have come up with nothing that's actually a realistic answer:

"A spectral line of hydrogen (wavelength 21.1cm in the lab) emitted by a galaxy is oversee to have a wavelength of 21.4cm. If Hubble constant has a value of 0.06 metres per second per parsec, how far is this galaxy from Earth (in parsecs)? Given c=3x10^8."

Can anyone provide an insight into how to go about doing this question?

Posted from TSR Mobile
Do you know the doppler shift equation? You can use it to calculute the recessional velocity of the galaxy from the change in wavelength and hence the distance.
3. I believe it's (measured wavelength - true wavelength) / true wavelength = v/c. I don't see how you get the distance from that without a time?
4. I also came across a formula which gives velocity = hubbles constant x distance but I got 7.11E7 when I used both of these and not certain whether that's a realistic value (or if that distance is actually in parsecs)
5. Still need help with this if anyone will?

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