Actually if you take a few light years at light speed without something to deflect or absorb energy from free floating hydrogen and dust your ship would be destroyed before you even reach the closest star outside our solar system. and they constantly say light from anything far away goes through alot of gases and stuff which is why they can see some of it in the first place.

Also at least 1 ok art of f hydrogen or dust poo er square meter. That's alot of stuff over several light years.