Hubble time in cosmology means the estimated age of the universe and the best calculation for it is T=1/H, where H is the Hubble constant
        
             
        
        
        
Since U=0, 
h=1/2gt^2 (h= ut+1/2gt^2, U=0)
h=1/2*10*4*4
h=80m
        
             
        
        
        
Answer:
use their own matter to create nuclear reactions
generate their own energy
are classified primarily by temperature
usually seem bright if they are close to Earth
Explanation: