Zodiacal light

Zodiacal light in the eastern sky before dawn twilight begins
Astronomers at ESO's sites often see zodiacal light.

Zodiacal light (also called false dawn[1][2][3] when seen before sunrise) is a faint, diffuse, and roughly triangular white glow that is visible in the night sky and appears to extend from the Sun's direction and along the zodiac, straddling the ecliptic.[4] Sunlight scattered by interplanetary dust causes this phenomenon. Zodiacal light is best seen during twilight after sunset in spring and before sunrise in autumn, when the zodiac is at a steep angle to the horizon. However, the glow is so faint that moonlight and/or light pollution outshine it, rendering it invisible.

The brightness of zodiacal light decreases with distance from the Sun. In naturally dark night skies, the glow is visible as a band along the entire zodiac, completely straddling the ecliptic. In fact, zodiacal light spans the entire sky and largely[5] contributes to the total natural light in a clear and moonless night sky. Another phenomenon – a faint but slightly brighter oval glow – directly opposite of the Sun's direction is the gegenschein, which is caused by backscattered sunlight.

The interplanetary dust in the Solar System collectively forms a thick, pancake-shaped cloud called the zodiacal cloud, which straddles the ecliptic plane. The particle sizes range between 10 and 300 micrometres, most with a mass around 150 micrograms.[6]

Viewing

Zodiacal light seen behind the Submillimeter Array from the summit of Mauna Kea

In the mid-latitudes, the zodiacal light is best observed in the western sky in the spring after the evening twilight has completely disappeared, or in the eastern sky in the autumn just before the morning twilight appears. The zodiacal light appears as a column, brighter at the horizon, tilted at the angle of the ecliptic. The light scattered from extremely small dust particles is strongly forward scattering, although the zodiacal light actually extends all the way around the sky, hence it is brightest when observing at a small angle with the Sun. This is why it is most clearly visible near sunrise or sunset, when the sun is blocked, but the dust particles nearest the line of sight to the sun are not. The dust band that causes the zodiacal light is uniform across the whole ecliptic.

The dust further from the ecliptic is almost undetectable except when viewed at a small angle with the sun. Thus it is possible to see more of the width at small angles toward the sun, and it appears wider near the horizon, closer to the sun under the horizon.

Other Languages
Afrikaans: Sodiaklig
العربية: ضوء بروجي
azərbaycanca: Zodial işıq
català: Llum zodiacal
Deutsch: Zodiakallicht
Ελληνικά: Ζωδιακό φως
español: Luz zodiacal
فارسی: صبح کاذب
galego: Luz zodiacal
한국어: 황도광
italiano: Luce zodiacale
Lëtzebuergesch: Zodiakalliicht
lietuvių: Zodiako šviesa
മലയാളം: രാശിപ്രഭ
Nederlands: Zodiakaal licht
日本語: 黄道光
norsk nynorsk: Zodiakallys
Piemontèis: Lus zodiacal
português: Luz zodiacal
slovenčina: Protisvit
slovenščina: Zodiakalna svetloba
srpskohrvatski / српскохрватски: Zodijačka svjetlost
svenska: Zodiakalljus
اردو: صبح کاذب
Tiếng Việt: Ánh sáng hoàng đạo
中文: 黃道光