Friday 31 December 2021

The Quadrantid Meteor Shower.

The Quadrantid Meteor Shower is one of the brightest meteor showers of the year, often producing over 100 meteors per hour at its peak, which falls on the night of 3-4 January each year, and is predicted to peak at about 10.00 pm GMT on Monday 3 January 2022; as this is only a day after the new moon, which fells on Sunday 2 January 2022, visibility for the shower could potentially be very good this year. The meteor shower originates in the constellation of Boötes, high in the northern sky, which is slightly confusing, as most meteor showers are named for the constellation in which they originate. This is because the constellation was named in the sixteenth century by astronomer Tycho Brahe, before the introduction of standardised constellations used by modern astronomers, though to make matters a little more confusing, Brahe didn't name the meteors this way either; the name comes from the constellation of Quadrans Muralis, introduced by Joseph Jérôme Lefrançois de Lalande in 1795, and dropped by the International Astronomical Union in 1922. Because Boötes is visible only from the Northern Hemisphere, the Quadrantid Meteor Shower is not visible from the Southern Hemisphere, and is best viewed from northerly locations such as Canada or Scandinavia.

The radiant point of the Quadrantid Meteors (i.e. the point from which the meteors seem to radiate). Greg Smye-Rumsby/Astronomy Now.

Meteor streams are thought to come from dust shed by comets as they come close to the Sun and their icy surfaces begin to evaporate away. Although the dust is separated from the comet, it continues to orbit the Sun on roughly the same orbital path, creating a visible meteor shower when the Earth crosses that path, and flecks of dust burn in the upper atmosphere, due to friction with the atmosphere.

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

The Quadrantid Meteors are unusual in that they typically are only visible for a few hours either side of this peak, whereas other showers are typically visible for days or even weeks. This is thought to be because they originate from an asteroid (196256) 2003 EH1, rather than the tail of a comet as with most meteor showers. The orbit of this asteroid is tilted at an angle of 71.9° to the plane of the Solar System, so that the Earth only very briefly passes through the debris trail left by it, rather than remaining in it for some time, as is the case with the trail of a comet with an orbit in roughly the same plane as the Earth.

The calculated orbit and current position (196256) 2003 EH1.  JPL Small Body Database

(196256) 2003 EH1 is a 2.6-4.0 km diameter object with a 2017 day (5.52 year) orbital period, with an elliptical orbit tilted at an angle of 70.8° to the plain of the Solar System which takes in to 1.19  AU from the Sun (119% of the distance at which the Earth orbits the Sun) and out to 5.05 AU (505% of the distance at which the Earth orbits the Sun slightly inside the orbit of the planet Jupiter). This means that close encounters between the asteroid and Earth happen occasionally, with the last calculated to have happened in December 1936 next predicted in December 2052.  It is therefore classed as an Amor Group Asteroid (an asteroid which comes close to the Earth, but which is never closer to the Sun than the Earth is). (196256) 2003 EH1 also has occasional close encounters with the planet Jupiter, with the last having happened in June 1984, and the next predicted for March 2044.

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