Saturday, 9 October 2021

The Southern Taurid Meteors.

The Southern Taurid Meteor Shower is expected to peak on Sunday 10 October 2021, the first of two overlapping meteor showers associated with the constellation of Taurus, the second being the Northern Taurids which will peak on Friday 12 November. The showers take their name from the constellation of Taurus, where their radiant point (the point from which they appear to radiate) can be found. At peak activity this meteor shower only produced about five meteors per hour, however, they are typically quite bright and therefore relatively easy to spot, and since the shower occurs shortly after the New Moon on 6 October, viewing should be fairly good this year.

 
The radiant points of the Southern and Northern Taurid meteor showers. EarthSky.

Meteor showers are thought to be largely composed of material from the tails of comets. Comets are composed largely of ice (mostly water and carbon dioxide), and when they fall into the inner Solar System the outer layers of this boil away, forming a visible tail (which always points away from the Sun, not in the direction the comet is coming from, as our Earth-bound experience would lead us to expect). Particles of rock and dust from within the comet are freed by this melting (strictly sublimation, transforming directly from a solid to a gas due to the low pressure on it's surface) of the comet into the tail and continue to orbit in the same path as the comet, falling behind over time. 

 
The Earth passing through a stream of comet dust, resulting in a meteor shower. Not to scale. Astro Bob.

The Southern Taurid Meteor Shower is caused by the Earth passing through the trail of Comet 2P/Encke, this is particularly spread out, so that the Earth takes several weeks to pass through it. This is thought to be because Encke is a remnant of a much larger Comet, which has broken up over the past 20 000 to 30 000 years, giving a long, spread-out debris stream.

 
How the passage of the Earth through a meteor shower creates a radiant point from which they can be observed. In The Sky.

Comet 2P/Encke was first observed by French astronomer Pierre M├ęchain in 1786, but gets its name from the German astronomer Johann Franz Encke, who calculated its orbit in 1818. The designation 2/ implies that it was the second Periodic Comet (comet with an orbital period of less than 200 years) ever discovered.

 
Composite image of Comet 2P/Encke made from six 60-second exposures taken with the 16"-f/35 Tenagra III robotic telescope at Tenagra Observatories in Arizona on 21 February 2017. Gianluca Masi/Virtual Telescope/Michael Schwartz/Tenagra Observatories.

Comet 2P/Encke completes one orbit every 1204 days (3.3 years) on an eccentric orbit tilted at 11.8° to the plane of the Solar System, that takes it from 0.34 AU from the Sun (34% of the average distance at which the Earth orbits the Sun, and inside the orbit of the planet Mercury) to 4.09 AU from the Sun (4.09 times as far from the Sun as the Earth, considerably more than twice the distance at which the planet Mars orbits the Sun).  As a comet with an orbital period of less than 200 years 2P/Encke is considered to be a Periodic Comet; it also gives its name to the Encke Group of Comets, which have orbits entirely within that of Jupiter.

 
The calculated orbit and current position of 2P/Encke. JPL Small Body Database.

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