When we step outside on a moonless night and gaze up at the sky, it may not appear to be as dark as we imagine it to be. The presence of streetlights and porch lights, especially the bluish-white LEDs that have become increasingly common, create a background glow that fills the air. This light pollution in our neighborhoods hinders our ability to see more than just a few bright stars. Even in rural areas, the illumination is such that the majestic sight of the Milky Way is often concealed from view. Astonishing as it may seem, only about a quarter of children in North America and Europe have actually seen the Milky Way with their own eyes. To truly experience the dark expanse of the night sky, one must venture to remote corners of our planet. The Andean desert in Chile, home to several major observatories, offers some of the darkest skies in the world, providing a matchless opportunity to witness the wonders of the universe.
Unveiling the true darkness of the cosmos requires escaping the clutch of light pollution. And the best way to achieve this is by exploring the most remote regions on Earth. Andean desert in Chile is one such place, where major observatories are situated, enabling stargazers to witness skies as dark as one could possibly hope for. In this serene setting, on a moonless night, the Milky Way shines resplendently, painting the sky with a plethora of stars and shadow constellations. The magnificent galactic center mesmerizes observers with its multicolored glow, while the Milky Way itself casts a faint and ethereal shadow when viewed with completely adapted eyes. However, even in this pristine location, complete darkness remains elusive.
Our atmosphere plays a role in ensuring that darkness is never truly attained. Even on the darkest night, a faint glow emanates from the atmosphere. This glow, known as airglow, arises due to the ionization of Earth’s upper atmosphere by ultraviolet sunlight and cosmic rays. Though not noticeable when we look directly overhead, it restricts the view of telescopes based on Earth. Consequently, some of the best observatories around the world are still affected by light pollution, leading scientists to turn their gaze towards the heavens.
A Pure View from Space
In an effort to escape the constraints of Earth’s atmosphere, telescopes such as the Hubble and Webb have been launched into space. With no atmospheric interference, these space-based observatories are able to capture breathtaking images of the cosmos. However, even they fall short of capturing the true darkness of the night sky. The glow of sunlight, known as sunglow, is a persistent issue that permeates our Solar System. Dust particles scattered throughout our solar neighborhood reflect light back towards Earth, resulting in the zodiacal light, which is faintly visible from space. Hence, while interplanetary space may be dark, it remains insufficiently so.
Into the Outer Reaches
To genuinely experience the darkest skies, one must journey far beyond the realm of dust and venture to the outermost edges of our Solar System. This unfathomable expanse lies beyond the orbit of Pluto, a realm explored by the Voyager and Pioneer spacecrafts. Although contact with the Pioneers has been lost, the Voyagers still communicate with us, albeit unable to transmit images. However, there is one spacecraft that holds the potential to capture the elusive darkness of the Universe – New Horizons.
Having flown past Pluto in 2015 and the Kuiper Belt Object Arrokoth thereafter, New Horizons now finds itself twice as distant from the Sun. Equipped with powerful cameras, it continues to gather valuable data. Recently, the New Horizons team aimed their instruments at a specific patch of sky – far away from the Milky Way, the Sun, and bright stars – in an attempt to measure the darkness of the Universe. Comparing the amount of light captured by New Horizons with Hubble’s view of the dark sky, researchers discovered a slightly darker picture, as expected. However, there remains an unexplained faint glow that intrigues astronomers.
The Quest for Answers
The discrepancy between Hubble’s observations and New Horizon’s measurements has given rise to questions about the nature of this mysterious background glow. To provide further insight, the team plans to observe 15 other dark locations over the next month, hoping to witness the naked dark expanse of the cosmos and, perhaps, unravel the enigma that shrouds this lingering glow. It is through these darkest skies that scientists may finally perceive the light that reveals the secrets of the Universe.
The true darkness of the night sky remains an elusive phenomenon, even in the most remote corners of our planet. Earth-based telescopes wrestle with light pollution and atmospheric glow, while space-based observatories still contend with scattered light from our Solar System. However, the journey does not end there. In the expanse beyond Pluto, the New Horizons spacecraft holds promise for unveiling the mystery of the darkest skies. As scientists continue to explore and observe, we inch closer to understanding the nature of the Universe and the profound beauty that lies within its depths.