One, three, four, two; seven, eight, six, five.
Size, we're told, doesn't matter.
But if it did, there's the answer!
Four solid, yet light. Four airy, yet heavy.
One stands crooked, one has a twin.
One's got an eye, like one in a picture.
But there is another! A big one!
This one's not like the others:
That which holds it all together.
A few more attributes, our mystery has:
Two belts! One of them holds a member
That was once thought to be another.
What is the name of the collection of members that this poem describes?