Zodiacal light

Zodiacal light in the eastern sky before the beginning of morning twilight.
Astronomers at ESO's observatories often encounter zodiacal light.

Zodiacal light is a faint, diffuse, and roughly triangular white glow visible in the night sky that appears to extend from the vicinity of the Sun along the ecliptic or zodiac. [1] Sunlight scattered by interplanetary dust in the zodiacal cloud 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 zodiacal light decreases in intensity with distance from the Sun, but in naturally dark skies, it is visible as a band completely around the ecliptic. In fact, the zodiacal light covers the entire sky and is largely responsible [2] for the total natural skylight on a moonless, clear night. Another phenomenon—a faint, but slightly brighter, oval glow—directly opposite of the Sun is the gegenschein.

The dust in the Solar System forms a thick, pancake-shaped cloud collectively known as the zodiacal cloud, which straddles the ecliptic plane. The dust particles are between 10 and 300 micrometres in diameter, most with a mass around 150 micrograms. [3]


Zodiacal light seen with a green and red Orionid meteor striking the sky below the Milky Way and to the right of Venus

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
català: Llum zodiacal
Deutsch: Zodiakallicht
Ελληνικά: Ζωδιακό φως
español: Luz zodiacal
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
Tiếng Việt: Ánh sáng hoàng đạo
中文: 黃道光