Encyclopedias by definition aren't primary sources.
Much less so, one that can be edited in realtime by anybody with Internet access. I use it the same way you do, the way our parents might have used the encyclopedias they bought "for the children" from the door-to-door salesman.
[I discovered Chesley Bonestell in my family's set, at a tender age: the entry on the Solar System had color plates of some of his paintings tipped in.]