“Touch not with iron that part of the body ruled by the sign the moon is transiting,” commanded an ancient medical-astrology tract. Meaning, since Taurus rules the neck and throat, you should not get a cyst removed from your neck when the moon is in Taurus. Likewise, no hysterectomies when the moon is in Scorpio (the ruler of sex organs).

We don’t talk much about lunar cycles in the average doctor’s office today, but this doesn’t mean timing is irrelevant in modern medicine.

According to one bit of popular lore, you should avoid being hospitalized in July, when that year’s graduating medical students begin working as residents. Every physician has to have a first day, but in the U.S. system, July 1 is everyone’s first day. Could this confluence of rookie doctors mean more medical errors? Researchers at Johns Hopkins reviewed almost 3,000 surgeries for spinal metastases and found a higher rate of complications during July surgeries, as well as a higher mortality rate [1]. Still, other studies have found that surgical outcomes are no worse in July than in any other month, perhaps due to increased vigilance by senior doctors [2].

Which is not to say that the calendar doesn’t make a difference: people admitted to the hospital on an emergency basis on public holidays are, compared with patients admitted on non-holidays, 48 percent more likely to be dead one week later [3]. The clock matters, too: with each hour that passes on a given day of performing colonoscopies, the average gastroenterologist is 4.6 percent less likely to detect a colon polyp [4]. Similarly, in a study of surgeries at Duke University Medical Center, the likelihood of problems related to anesthesia increased from a low of 1 percent during surgeries starting at 9 a.m. to a high of 4.2 percent for those starting at 4 p.m., possibly because practitioners grew tired over the course of the day [5].