At 7.23pm (11:23am GMT), the gap between the Earth and the moon was close to its shortest point, known as “perigee” – a distance of 356,510 km. Little bears joined the other lunatics in Kings Park to watch the event.
Tonight the moon became full within about two hours of perigee – making it an extra-supermoon. At the same time (around 1:30pm GMT), the Earth, sun and moon will be almost perfectly in a line (an effect known as a “syzygy”), with the moon directly opposite the sun. So essentially the moon is at its closest when it’s also at its fullest.
There are a number of other subtle effects that cause the moon’s orbit to vary slightly in size and shape, but this one pips the last few decades’ worth of super perigee full moons by a few hundred kilometres. In November 2034, when we’ll have a similarly big supermoon, it will occur within a few minutes of its closest approach, and even then it will be just 100km closer than today’s full moon.
Supermoon is not an astrological term. It’s scientific name is perigee-syzygy, but supermoon is more catchy. Since the moon has an elliptical orbit, one side of the orbit (the perigee) is about 48,000 kilometres closer to Earth than the other side (the apogee). When the Earth, moon and sun line up in an orbit, while the moon is on its nearest approach to Earth, we are treated to a so-called supermoon.