Assuming that these two circles were created with the circle (Ellipse) Tool then you could use the Pen Tool and have Smart Guides on, place a point at the center of the circle #1, lock the point in the layers panel, repeat the steps for circle #2, unlock both points in the layers panel and then select Paths>"join" but that seems like a lot of work when you could just drag a line using the Line tool and Smart Guides on between the centers of the two circles.
It seems a bit strange to want to create an action for this since any constellation is not that complex and just selecting the two circles is about as complex as drawing the line and would take the same time and that would be excluding the invocation of the action. ?
Why do you think you need this?
Thanks for your reply. My description of creating a constellation star map, is an oversimplification of the scope of my project. The time consuming part is locating the exact center of the small circles. I assume that I'll have to draw each segment by hand, but I thought it'd be worth asking if there was a shortcut.
With View>Smart Guides ticked, as mentioned in the first post, it should be very easy to select the Pen Tool, move the cursor to the centre of the first circle, close enough to wake it up (a cross and the word Center turning up), click it, and then do the same over the other the next circle.