Last week saw two interesting astronomical phenomena, a ‘supermoon’ and the peak of the annual Perseid meteor shower.
The moon’s orbit around the Earth is elliptical rather than circular, which means that sometimes it is closer to the Earth and sometimes further away. As a result, the distance between the moon and the Earth varies by about 238,000 miles. If the moon is at its closest to the Earth when it is full it is referred to as a ‘supermoon’, whereas a full moon occurring at the furthest point of its orbit is referred to as a ‘micro moon’.
A supermoon occurs, on average, every 13 months, and appears around 16% larger than a micro moon, and over 40% brighter. Last week’s supermoon was bigger and brighter than it has been for 20 years, and astronomers feared that it would reduce the number of shooting stars visible during the Perseid meteor shower.
A meteor is a particle, often no larger than a grain of sand, travelling at thousands of miles per hour through the Earth’s atmosphere and burning up in the process. It appears as a streak of light moving rapidly across the sky. The Perseid meteors originate from the comet Swift-Tuttle. Comets contain ice, which becomes gas as the comet approaches the sun, and the exploding jets of gas pull dust out of the comet into its orbit. As the Earth passes through the orbit, which happens at the same time each year, the dust produces a meteor shower.
The Perseid meteor shower appears every year from mid-July until late August, peaking at around 12 August when it can produce more than 80-100 shooting stars per hour. It is named after the constellation Perseus, from which the meteors appear to radiate. Perseus was a Greek hero who killed the one-eyed Gorgon, Medusa. Medusa’s head was covered in snakes in place of hair, and anyone who looked at her was turned to stone. So Perseus used a mirror to slay her without looking directly at her.
By the fifth century BC most of the constellations had become associated with ancient myths. However, around AD 150 the Roman Ptolemy produced a catalogue in which he grouped over a thousand stars into 48 constellations, including Perseus. The catalogue gave the latitude and longitude of each star, its brightness, and the constellation to which it belonged.