What does counterglow mean?
The counterglow is a faint, diffuse patch of light that appears in the night sky at a point directly opposite the sun — the so-called antisolar point. It arises when sunlight reflects off a cloud of interplanetary dust particles concentrated along the plane of the solar system, scattering light back toward the observer. The phenomenon was first described by Danish astronomer Theodor Brorsen in the nineteenth century and is more widely known by its German-derived name, the gegenschein. Observing the counterglow requires exceptionally dark skies, free of moonlight and artificial illumination, which makes it one of the more elusive sights available to amateur astronomers. Though subtle, it offers direct evidence of the dusty environment through which the Earth moves, and it remains a subject of interest in studies of interplanetary matter.
nounA faint glow in the night sky appearing at a point directly opposite the sun; an astronomical phenomenon also known as the gegenschein.
- A faint luminous patch visible on very dark nights at the antisolar point — directly opposite the sun's position — caused by sunlight reflected off interplanetary dust in the ecliptic plane.
"On the darkest nights, observers at high altitudes can sometimes detect the elusive counterglow opposite the sun."
"From the mountaintop observatory, away from all city lights, the astronomers could just make out the faint counterglow opposite the setting sun."
"The zodiacal counterglow, though difficult to observe, provides evidence of the vast cloud of interplanetary dust surrounding the sun."
Rarely pluralized, since only one counterglow is observable from any given point at any time; the plural would apply only in theoretical or multi-perspective contexts.
"Observers on different planets would each see their own counterglows at their respective antisolar points."
"Counterglow" is simply the English translation of the German "Gegenschein" — literally "counter-shine" — a ghostly patch of light that hides in plain sight directly opposite the sun in the night sky.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of counterglow
The word counterglow combines "counter-," from Latin "contra" meaning "against" or "opposite," with "glow," from Old English "glōwan," meaning to shine or glow. It arose as an English equivalent of the German "Gegenschein" (literally "counter-shine"), coined in the mid-nineteenth century to describe this antisolar phenomenon. Other words built on the same "counter-" element include "counterpart" and "encounter."
How counterglow is actually used
Counterglow is a technical astronomical term used mainly by amateur and professional astronomers; it is far less common than its synonym "gegenschein." It is best observed from very dark sites and can be challenging even for experienced observers.
Easily confused with counterglow
Airglow is a faint, permanent luminescence of the upper atmosphere occurring everywhere in the sky, whereas counterglow is a specific patch of light always located directly opposite the sun.