The not so super Supermoon

Each 29 days the moon rotates around Earth. Moon’s orbit’s not circular, but egg-shaped. So there’s a point at which it’s closest to Earth. This point’s called the lunar perigee. It’s not a fixed distance. On average it’s 364,397 kilometres. But two nights ago it was 356,577 kilometres. This is the closest the moon’s been to Earth since 1993. When one lunar perigee’s in the lowest 10% of the range of all lunar perigees, the moon’s called a Supermoon [1, 2, 3]. When the moon’s at perigee it exerts more gravitational pull, creating higher tides (and a bigger difference between high and low tides). So a Supermoon causes high tides that are slightly higher than normal. And it has some impact on seismic activity due to the stronger gravitational pull between the sun, the moon and Earth. But even so, there’s no clear evidence the Supermoon was a causal factor in the earthquate and tsunami that hit Japan on 11 March – which was eight days before the Supermoon. On 11 March the moon was at an average distance from Earth. The 19 March Supermoon was about 20% brighter and 15% bigger than an average full moon. These increases were insufficient to be noticeable to the casual observer. But that didn’t prevent media hype [4]. I was tempted to look. But the entire time between moonrise at 7:28 p.m. on 19 March and moonset at 6:55 a.m. on 20 March, the Mole Creek sky was in full cloud. Ho hum.

P.S. Still on matters astronomical, happy southern hemisphere autumnal equinox to you.