The Zodiacal light is a rarely seen yet intriguing spectacle in a dark sky. Sinead McNicholl reveals the connection between the zodial light and a famous rockstar!
Have you ever noticed a whitish glow in the night sky which appears to extend upwards in the shape of a triangle or pyramid? Over the next month, on some clear moonless evening, if you are lucky enough to be far from any light pollution, keep a watch on the western horizon just after sunset and you might just see this column of light in the night sky. What is this ghostly light display? Well, I thought I would shed some “light” on this phenomenon and find out what exactly it is!
This strange glimmer in the night sky is visible after sunset or just before dawn and at certain times of the year it can be observed with the naked eye. It has also been known as a ‘false dawn’ down through the years as it is often confused with the light of the dawn, but its proper title is Zodiacal light. Giovanni Domenico Cassini (1625 -1712) was the first astronomer to investigate Zodiacal light and came to the conclusion in 1683 that it was of cosmic origin and not meteorological as some had previously thought. However, it was a Swiss mathematician, Nicolas Fatio de Duillier (1664 -1753) who became the first person to successfully explain the nature of Zodiacal light in 1684. In fact this was personally his greatest success.
Basically the display is caused by sunlight reflecting on dust that is floating in orbit around the Sun. This cosmic dust lies in the plane of our Solar System (also called the ecliptic) which holds the path of the Sun, the Moon and the planets. This pathway is called the Zodiac or the Pathway of Animals as the constellations which fall within this path are the ones that we know today as the signs of the Zodiac (you might know them from reading your horoscope at the back of a magazine!). These grains of dust can range in size from being as small as a grain of sand to meter-sized objects.
Zodiacal light can be quite bright, clearly visible to anyone who looks in the hours after dusk, or before dawn. The best times for viewing are during moonless nights in the months of February and March looking west just after evening twilight, and October provides us with the display just before morning twilight in the east. It can even be bright enough to become a nuisance to amateur astronomers attempting to view objects in the night sky through their telescopes. At the same time it is a sign of good clear dark skies, as it is otherwise hidden by the glow of artificial light. The slightest amount of moonlight or light pollution and this glow disappears from our sight.
An interesting fact is that it can only be seen with the unaided eye and is not visible through optical instruments such as telescopes and binoculars. This is because it has a low surface brightness and large size. It can also been seen in the southern hemisphere, the video below from the European Southern Observatory shows timelapse footage of zodiacal light in Chile.
We are still learning about this spectacle of light in the sky. Until recently we thought that the dust originated from the tails of comets and collisions between asteroids in the asteroid belt, but last year (2010) a new theory was proposed. In an article in the Astrophysical Journal, David Nesvorny and Peter Jenniskens attributed over eight-five percent of the cosmic dust to be fragmentations of Jupiter Family Comets. The gas giant planet’s strong gravitational pull scatters dust from these comets, according to the study. This dust then falls into orbit around the sun, continuously replenishing the zodiacal cloud.
A minimal amount of research on this topic has been carried out. This is emphasised by the fact that in August 2007 Brian May, (Yes, he was the lead guitarist with the band Queen), handed in his PhD thesis on zodiacal light thirty-six years after first starting it! Perhaps a good title for his thesis would have been ‘Another one bites the dust’, but he entitled it “Radial Velocities in the Zodiacal Dust Cloud” (A great name for an album, don’t you think?) At the time he had abandoned his studies in favour of pursing a career in music, but in 2006, after finding his unfinished thesis in the attic, he decided ‘The Show must go on’ and swapped his guitar for a telescope! A little interesting aside is that Dr. May also has an asteroid called after him; Asteroid 52665 Brianmay was named in his honour on 18 June 2008.
Although zodiacal light it is an eerie sight, it is a spectacle that you will remember, so this month get outside and spot this interstellar cosmic dust! We have a New Moon phases on 3 March. Let us know if you see it!
Article by Sinead McNicholl.