NIGHT WATCH
The super moon – an astronomer’s kryptonite
The term “super moon” gains more traction in the media every year, much to astronomers’ irritation. American astrologer Richard Nolle coined the term in 1979 to market a book he’d written: According to him, a full moon becomes a super moon when it’s “near its closest approach to earth in a given orbit”. Nolle calculated the “closest approach” by taking the difference between the moon’s furthest and closest points to the earth in a given year and working out 90 % of that figure, then subtracting it from the furthest point. In 2019, the calculation will work like this: The moon’s furthest point from earth will be 406 555 km on 5 February; later that month on 19 February it will reach its closest point: 356 761 km. The difference between the two points is 49 794 km; 90 % of which is 44 814 km. Now, subtract 44 814 km from the furthest point and you get 361 741 km. According to Nolle’s definition, any full moon closer to the earth than 361 741 km will be a super moon. So complicated – and arbitrary! Nolle’s definition allows for more than one super moon per year. Maybe he allowed for so many super moons in order to support his theory that a super moon can cause natural disasters on earth. The more super moons, the better the chances of one coinciding with a natural disaster! Of course this isn’t true: The moon moves close to the earth every month, just not always during full moon. According to the Nolle calculation, there will be three super moons in 2019: 21 January, 19 February and 21 March. The full moon in February will be closest to earth (356 846 km) and the biggest full moon of 2019. But it won’t be massive. In fact, the effect will be hardly noticeable to the naked eye. The best way to see the difference in size and brightness between a “normal” full moon and a super moon is to take photos of both using identical focal lengths and exposure settings.