It’s the largest feature in the solar system visible to the naked eye, and yet most people have never seen it, explained Richard Fleet, talking about the elusive zodiacal light. In a single exposure taken from the Cerro Tololo Inter-American Observatory (CTIO) in Chile, astrophotographer Petr Horálek was able to combine that ethereal glow with the fiery center of the Milky Way, making a bright ‘X’ over the Andes.
The galactic core of the Milky Way, a tight grouping of stars, nebulae, and interstellar dust, is brightest from the Southern Hemisphere, where Scorpius, Sagittarius, and Ophiuchus come up high in the sky. From CTIO’s vantage point at 2,200 meters in the Atacama Desert, the atmosphere is thin, arid, and free of most light pollution conditions that let the galaxy’s complex dust lanes and star clouds break out in stunning detail. Southern viewers have a more oblique angle of view to the core than northern viewers, and it shows rich objects like the Lagoon Nebula and the Carina Nebula in dramatic detail.
The second beam in Horálek’s photo, the zodiacal light, is much more subtle to the human eye. It appears as a dim, triangular column near the ecliptic, and it is sunlight scattered by a huge disk of dust particles that move around the Sun. Its birth was disputed for centuries. Asteroid impacts or comet fragments were early hypotheses, but new spacecraft information has changed the picture. NASA’s Juno mission to Jupiter became a serendipitous dust observatory after its star- tracking cameras captured thousands of high-speed collisions minute grains at about 16,000 km/h. Analysis showed that most of these particles move in nearly circular orbits between Mars and just beyond Earth, their numbers following the distribution of orbital elements of the Red Planet.
The discovery indicates that Mars, the planet most heavily coated with dust, could be a main source of the zodiacal cloud. How the particles break free of Mars’ gravity is still an open question, although global dust storms are the prime suspect. Jupiter’s gravitational pull creates a barrier at around 2 astronomical units, which stops the dust from escaping into outer space and trapping it within the inner solar system. Material trapped this way, when bathed in the Sun’s light, is the biggest visible feature in the solar system a glowing veil across the night.
Capturing zodiacal light as an astrophotographer takes a lot of planning. The most intense glow occurs near the equinoxes, when the ecliptic is steeply inclined relative to the horizon. In the Southern Hemisphere, it shows up after darkness from late August to early November and before dawn from late February to early May. A moonless night and a dark location distant from artificial light are necessary; even the slightest skyglow can obliterate it. Long-exposure photography, usually with wide-angle lenses between 14–24 mm, shows its full range and nuanced gradations.
Horálek’s location at CTIO put him alongside some of the world’s most sophisticated optical equipment, including the U.S. Naval Observatory Deep South Telescope and the Planetary Defense 1.0-meter Telescope. These facilities are located here for the same reasons astrophotographers converge on the Atacama: calm atmospheric conditions, low water vapor, and some of the darkest skies on the planet. These conditions not only increase visual contrast but also minimize scattering, enabling faint objects such as the zodiacal light to be prominent against the star field.
In the composite, the Milky Way’s vertical arc crosses the zodiacal beam to create a natural cross of galactic and solar system light. The contrast highlights the layered complexity of the night sky our galaxy’s central bulge tens of thousands of light-years distant, the zodiacal dust mere millions of kilometers from Earth. To the trained eye, it is also a reminder that astrophotography is as much a matter of timing and geometry as of optics.
Scientifically, such images are more than just visual triumphs. They offer visual validation of dust distribution models, aid in the honing of scattering simulations, and encourage public engagement with phenomena that are in growing danger of being destroyed by light pollution. As NASA’s Goddard Space Flight Center’s Jack Connerney pointed out, “Each piece of debris we tracked records the impact of an interplanetary dust particle, allowing us to compile a distribution of dust along Juno’s path.” That distribution, now anchored to Mars, could impact the design of future spacecraft to resist micrometeoroid impacts.
In Chile’s high desert, under such dark skies that the Milky Way has shadows, the crossing lines of Horálek’s photo provide both spectacle and data a unusual convergence of science and beauty translated in starlight and in dust.
