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Are You Looking at the Same Moon?

This post was originally published in Capella: The Cambridge Astronomical Association newsletter.


In his 1997 top-ten (in Poland) hit-single “The Same Moon,” a then recently divorced Phil Collins asks his absent soulmate to choose a time when they could both look up at the titular lunar surface. Now, some two and a half decades later, it has come to my attention that TikTok users have taken this to a whole new level by asking if their soulmate’s birth moon phase matches up with their own. The so-called #MoonPhaseSoulmates trend involves overlaying images of the phases of the moon on a couple’s birth dates to see if they line up like one of those broken heart necklaces. This combination of elements intrinsic to all the most viral of TikTok trends: the gamification of personal data and the production of visually satisfying imagery, has proven unsurprisingly popular with the application’s youthful user base.


A consequence of this popularity is an abundance of these videos with an apparent match rate well above the 12.5% expected from the moon’s eight phases (ignoring, as the trend does, such complexities as tilt, angular size, and libration). However, while my own first quarter at 64.77% illumination fails to match well with my wife’s waning crescent at 28.83 illumination, I won’t be filling for divorce just yet. As I suspect this anecdotal data to be distorted by reporting bias as those, like me, whose moons didn’t match up are doubtlessly disincentivized from putting in the effort of producing a video and may even go so far as to fake their results in the pursuit of love (or possibly clicks). Although they needn’t have bothered as those same 8-1 odds suggest we all have around one billion soulmates waiting out there.


This already bias data set was further distorted by two more deviant developments the trend. First, in a process instantly recognisable as confirmation bias, as a slew of videos emerged showing the matching moons of BFFs, celebrities, and family members, while those that didn’t match were presumably quietly consigned to the file drawer of unreported data. Then, even more egregiously, post-hoc hypothesizing made even those moons that didn’t match up take on an apparent significance with the twin flames interpretation. In this variation if you and your partner’s lunar phases overlay each other exactly, rather than being soul mates, you share the same soul. An apparently rare phenomenon with again odds of around 8-1, bringing the chances of a significant result from this test up to 1 in 4.


Furthermore, there is a fatal flaw standing in direct opposition to the moon’s long association with love (and not just by former Genesis drummers) and peculiar proneness to romantic pseudoscience (with its phases unjustly blamed for everything from lunacy to lycanthropy) which this trend shares with its spiritual precursor of astrology. That flaw being that while the moon does indeed have a demonstrable effect on our planet in the form of tides, there is no known scientific mechanism by which its position (nor indeed that of any of the other celestial bodies) at the time of our births could have any significant effect upon our lives and/or loves. Proposed mechanisms including gravity, electromagnetism and even dark energy can largely be dismissed as the inverse square law makes their effect negligible at these extreme distances.


These trends tend to be fairly ephemeral affairs, and as this particular one is not it seems being taken particularly seriously it is, in my considered opinion, of no particular concern. What it is however is a reminder of a worrying post-pandemic resurgence in interest in astrology among the younger generations. And while we are far from the dark days of the 70s and 80s when astrologers were regularly consulted by the White House and a statement of concern was signed by 186 leading scientists, led by the astronomer Bart Bok and including such familiar names as Chandrasekhar, Drake, Hoyle, Oort and Thorne, we would do well to be on guard against the irrationalism and obscurantism that those signatories warned come with such magical thinking.


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