The lunar cycle is 29 days, and so is the average menstrual cycle, so somewhere along the way, people got the idea that the moon's phases controlled menstrual cycles. This is nonsense. If that were the case, there would be a run on menstrual products at the same time every month, papers would be written, and everyone would know about it. Besides, there is only one moon, but billions of women, with only an average cycle of 29 days. In reality, women vary in both cycle length and regularity.
See, correlation is not necessarily causation. But scientific studies tell us that a different celestial body may actually have an effect on menstrual cycles. Whether this has any significance for women's health or fertility is another question entirely, but at least we get a glimpse into sea urchin gonads from the folks at SciShow. This video has a 50-second skippable ad at 2:22. -via Geeks Are Sexy