The spectrum of a galaxy is observed to have an H$\alpha$emission line at a wavelength of 856.3 nm. What is its distance if the Hubble constant is 70 km/s/Mpc? Note that the rest wavelength of the H$\alpha$ emission line is 656.3 nm.

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The Answer of The spectrum of a galaxy is observed to have an H$\alpha$emission line at a wavelength of 856.3 nm. What is its distance if the Hubble constant is 70 km/s/Mpc? Note that the rest wavelength of the H$\alpha$ emission line is 656.3 nm.

The Spectrum of a Galaxy Is Observed to Have an H