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Why do we need the formula #v=H_oD# to measure the recessional velocity of a galaxy when instead we can just do #v=(dD)/(dT)#?

Answer 1

Hubble's formula is a correlation formula and is not in mathematical exactitude. The velocity of a galaxy is estimated by the Doppler effect. Galaxies appear to be receding from one another.

The definition of velocity is the rate at which a distance changes in relation to time; it ceases to function at discontinuities. The Doppler effect is the result of a light source's motion, which causes its wavelength to change.

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Answer 2

Levi Alexander

While v=(dD)/(dT) only takes into account the relative motion between the observer and the galaxy, the formula v=HoD is used to measure recessional velocity because it takes into account the expansion of the entire universe. The Hubble constant (Ho) in the first formula incorporates the overall rate of expansion, providing a more comprehensive measure.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.