The two BIG issues in Astronomy are: Dark Energy and Dark Matter.

These two things really are HUGE. Not knowing what they are is like hearing an elephant stomping around and trumpeting loudly in your garage and NOT being able to find the elephant. (I am talking about an ordinary two car garage with the lights on.) You look in your garage and there is no elephant, nonetheless, you can feel it stomping around had hear its blaring trumpeting WHILE YOU ARE WALKING AROUND IN THE GARAGE LOOKING IN BRIGHT LIGHT. You hear it and feel it shaking the garage, but you cannot touch it or smell it. But it IS there. Saying that it is an invisible, incorporeal elephant is just a cop-out.

DFM