As we all know the observatories' scanning ability is determined by the energy in it. However I've never seen the energy meter, is there none or am I simply not putting enough attention?

It is a counter when you click on the Observatory. I think (not sure at the moment) that it starts at 100. Each scan uses 25 and then it slowly recharges over time. The number of the energy level is in the bottom of the description in the middle of the display.

It starts at 25 .

I took a screenshot yesterday evening so I could look at it in peace, I finally found it now.