Sciency Thoughts: The Draconid Meteor Shower.

Tuesday 8 October 2019

The Draconid Meteor Shower.

The Draconids are one of the most notable annual meteor showers, in some years producing several thousand meteors per hour (like most meteor showers the number of Draconids varies from year to year). The shower is expected to peak on Wednesday 9 October 2018, with best viewing in the evening (this will b e the same wherever you are on Earth), though visibility may be somewhat hampered this year, as the meteor shower peaks slightly before the Full Moon on Sunday 13 October, so that the meteors may be obscured by the brightness of the Moon. The Draconids take their name from the constellation of Draconis, with the meteors appearing to radiate from the mouth of the Dragon, between the stars Eltanin and Rastaban. Since this constellation is very high in the northern sky, the Draconids are an almost exclusively Northern Hemisphere phenomenon, which sightings from south of the equator being quite rare.

The radiant point (point from which the meteors appear to radiate) of the Draconid Meteor Shower. AccuWeather.

The shower is caused by the Earth passing through the trail of the Comet 21P/Giacobini-Zinner, and encountering dust from the tail of this comet (for this reason the shower is sometimes known as the 'Giacobinid Meteors'). The dust particles strike the atmosphere at speeds of over 200 000 km per hour, burning up in the upper atmosphere and producing a light show in the process. The name 21P/Giacobini-Zinner implies that the comet was the 21st Periodic Comet discovered (a Periodic Comet has an orbital period of less than 200 years) and that it was discovered by Michel Giacobini, who first observed the comet from the Nice Observatory in France in 1900, and Ernst Zinner who observed the comet from the Remeis Observatory in Bamberg, Germany, in 1913.

Two-panel mosaic image of Commet 21P/Giacobini-Zinner, taken from the Los Padres National Forest in California on 17 August 2019. Tom Masterson/Transient Astronomer/Flikr.

The Earth does not need to pass close to 21P/Giacobini-Zinner for the meteor shower to occur, it simply passes through a trail of dust from the comet's tail that is following the same orbital path. Comet 21P/Giacobini-Zinner itself visits the Inner Solar System once every 6.6 years, last doing so in 2018, when it reached about 58 434 00 km (0.39 AU) from Earth on 11 September. The comet has an eccentric orbit tilted at 31.9° to the plane of the Solar System, that takes it from 1.03 AU from the Sun (103% of the average distance at which the Earth orbits the Sun) to 6.00 AU from the Sun (6 times as far from the Sun as the Earth,slightly outside the orbit of Jupiter).