ESOcast 82: Zodiacal Light

By | January 6, 2020

The Atacama Desert in northern Chile is famed for its dark night skies, which can be enjoyed in their full glory thanks to the absence of light pollution. But even the darkest sky is not completely dark. Astronomers at ESO’s observatories often encounter a natural light phenomenon above ESO’s telescopes known as the zodiacal light. This is the ESOcast! Cutting-edge science and life behind the scenes at ESO, the European Southern Observatory. Exploring the ultimate frontier with our host Dr J, a.k.a. Dr Joe Liske. Hello and welcome to another episode of the ESOcast! ESO’s observatories are such incredibly dark sites that normally the only thing that illuminates them on a moonless night is the faint light from the billions of stars in the Milky Way. But there are a number of other interesting phenomena that can be observed in the skies above the telescopes. These include, for example, the faint veil of airglow, and the occasional appearance of red sprites above the odd distant thunderstorm. And then, every night, especially in the hours just after dusk or before dawn, this faint, fuzzy column of light appears in the sky, just above the horizon, extending upwards. This ghostly glow is known as zodiacal light. Shortly after sunset, just as stars begin to appear in the sky, the first hints of zodiacal light also become visible. As darkness sweeps over the desert, this light becomes more prominent and can be seen as a bright column of light reaching up from the horizon. This luminous column follows the starry background across the sky, eventually disappearing below the horizon as the Earth rotates on its axis. Even after the brightest part of the zodiacal light has dropped below the horizon, traces of it are still present. Although it now resembles an extremely faint wispy bridge that brightens again in the early morning, just before daybreak. The origins of zodiacal light are to be found in the inner Solar System. The Sun is surrounded by tiny grains of ice and dust, that are constantly being replenished by crumbling icy comets and colliding asteroids. These grains are distributed within the same flat disc of space inhabited by the planets. When viewed from Earth this disc appears as a narrow path across the sky, called the ecliptic, which the Sun, Moon and planets all appear to follow as they move in the sky. Zodiacal light is created when light coming from the Sun is scattered forwards off the particles in this disc in the direction of Earth. When viewed from Earth, this creates the appearance of a continuous band of light along the ecliptic, that gets fainter as you look further away from the Sun. The constellations of the Zodiac of course also lie along the ecliptic, and that’s why we call this ghostly glow zodiacal light. Along the the ecliptic, high in the sky, an oval patch of illumination can also appear, known as Gegenschein or counter-glow. Named by the German explorer Alexander von Humboldt, this phenomenon is created by sunlight that is scattered backwards off interplanetary dust particles. It can be seen at the point in the sky opposite the Sun. A similar phenomenon can be experienced here on Earth. When you turn your back to the Sun in foggy weather, a halo of light called a glory sometimes appears around your shadow on the ground. The zodiacal light phenomenon seems to have been first investigated in the late 1600s, by the Italian astronomer Giovanni Cassini and the Swiss mathematician Nicolas Fatio de Duillier. They were absolutely fascinated with this light in the sky and, of course, back in the 17th century, there was very little light pollution, and so for them it was relatively easy to observe this phenomenon, even from cities. Modern observations have shown that the Solar System might not be the only one to exhibit zodiacal light. Data from the Very Large Telescope Interferometer at ESO’s Paranal Observatory has revealed that numerous other planetary systems are also surrounded by interplanetary dust. Zodiacal light is a really photogenic feature and so it’s no surprise that it’s become a popular subject for night-time photographers in the Atacama Desert. The fact that it’s so prominent at ESO’s observatories is a beautiful demonstration of how incredibly good the observing conditions at these sites actually are. This is Dr J signing off for the ESOcast. Join me again next time for another cosmic adventure. Transcription by ESO; translation by —

17 thoughts on “ESOcast 82: Zodiacal Light

  1. Brian Mahoney Post author

    These videos are priceless. Please keep on making them.

  2. Heizenberg Post author

    Thanks for the effort and the precious information . Keep going 👍🏻

  3. Mohamed Safras Post author

    This phenomena has been mentioned 1500 centuries ago in Islam, where as the Muslim worshiper are been asked to stay away from this Zodiacal light till the real dawn happen before they can initiate their prayers in the morning. It is called Fajr prayer and Zodiacal light here referred to as Fajr l-Kadib.

  4. Beadybonce Post author

    Kristian Birkeland was confident he had witnessed oscillations in the zodiacal light and went to Sudan in 1910 to study the phenomenon. Birkeland’s suspicion was that the pulsation in “the intensity and shape of the light … surely testifies to an electric origin …His conclusion, that the earth’s magnetic field affects both the path and the spread of electrically charged particles from the sun, and is therefore significant in the development of zodiacal light. Indeed, it would have to be akin to the pulsation which is sometimes seen in auroral lights and the oscillations in terrestrial magnetism.

  5. serge gainsbourg Post author

    Beautifully cool explanation …being once for a while in the desert of Atacama , I can confirm this marvellous spectacle from the outer space …!

  6. The Roaring Twenties Post author

    It must be the Magpie Bridge that the Ancient Chinese speak of. There are 1700 spots on earth that do this. Very little light pollution in the 1700s? Um, there was NONE, ZERO light pollution.

  7. Maria da Luz Moutinho Post author

    Que maravilha….Os efeitos fascinantes…Que bela partilha de informação, beleza e um fenómeno mui luminoso! Espantosamente absorta!! Simplesmente um espectáculo lindo!!!


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