I'm not sure if they simulate the moon accurately or not (and don't really care), but I'm using a pair of 12 volt cold-cathode neons designed for use in decorating a car inside the hood of my 29 gal ... got them from Meijer for ~$20 (a lot imho, maybe cheaper sources online?)
I think they also had 12" and 16" models, for those lucky enough to have bigger tanks :)
Gordon
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