Recessional_velocity
Recessional velocity
The rate at which an astronomical object becomes more distant from an observer
Recessional velocity is the rate at which an extragalactic astronomical object recedes (becomes more distant) from an observer as a result of the expansion of the universe.[1] It can be measured by observing the wavelength shifts of spectral lines emitted by the object, known as the object's cosmological redshift.
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