You're probably confusing this with the rule surrounding verifiable facts (ie, "I asked John if he was happy").
Subjunctive forms of verbs are typically used to
express various states of unreality such as wish,
emotion, possibility, judgment, opinion, necessity,
or action that has not yet occurred.
And yes, perhaps using the present tense would be more appropriate. Certainly I would have used something like:
The solar system plotted on a scale where the Moon is one pixel.
<Shrug /> It's the interwebs, people will write what they like, and declare that nothing is right, and nothing is wrong, it's all OK. In that case telling someone to use the subjunctive seems doubly inappropriate.