 Stars range in size from neutron stars , which vary anywhere from 20 to 40 km ( 25 mi ) in diameter , to supergiants like <unk> in the Orion constellation , which has a diameter approximately 1 @,@ 070 times that of the Sun — about 1 @,@ 490 @,@ 171 @,@ 880 km ( <unk> @,@ <unk> @,@ 878 mi ) . <unk> , however , has a much lower density than the Sun . 
