What is the Hubble Constant?

Question

If a number varies, then it's not a constant.,,, but the Hubble Constant seems to vary. Why?

And why is it important to us?

To what degree of accuracy can it be meaasured?

Answer 1

Here is the answer but remember, if this is a homework question, please do your own research and do not turn in these words as your homework.  Please rephrase my answer in your own words.

The Hubble constant is a proportionality constant in the Hubble Law which relates the speed a distant galaxy is receding away from us and the distance of that galaxy from us.  

V=Ho x D

where V is in km/s

D is in parsecs

Why is it important?

The Hubble Law is direct evidence of the Big Bang Theory (why is this?) and the Hubble Constant can be used to estimate the age of the Universe since the Big Bang

According to Wikipedia the Hubble Constant is

70.1 ± 1.3 (km/s)/Mpc.  this is a fairly accurate measurement because the uncertainty is so low.

Is it a true constant?

If the Hubble Constant is currently 70.1 ± 1.3 (km/s)/Mpc,  then it has that value everywhere in the Universe at this time, but in the distant past and the future, the universe may expand faster or slower, so this number may be seen to vary.  So while it is a universal constant, it may slowly change over time.