The Zodiacal Light

The Zodiacal Light is a real astronomical term which describes what historically has been referred to as the “false dawn”.  This very real phenomenon has been observed by man since ancient times, being described as a ghostly twilight which occurs just before true dawn, but appears more of an apparition with form (conical or pyramidal) rather than the true horizontal dawn.  Typically it occurs several or within an hour of the actual sunrise, and can blend contemporaneously with the actual sunrise or sun set twilight period.  The false dawn is probably more mentioned due to it’s medieval importance in night watches, even today in modern times. The Zodiacal Light can occur however at either dusk or dawn approaches.

Zodiacal light is produced by the reflection of sunlight (same spectra) from interplanetary, or cosmic dust particles which occur along the ecliptic ( the plane in which the planets orbit around the Sun), concentrated within the inter planet orbits.  This location of this space dust is known as the Zodiac Cloud.  The origin of the interplanetary dust is believed to be remnant cometary dust and from asteroid collisions scattered throughout the orbits of the inter planets.  The size of the dust grains are on the order of micro millimeters, and spread very thinly throughout the Zodiac Cloud.

Image
Credit: ciber.caltech.edu

The best time for viewing is Spring and Autumn, due to the steep inclination of the ecliptic plane with the Earth’s horizon.  The Zodiac is simply those constellations which appear along the planets orbits, or within the ecliptic plane.  The light is very faint, similar to the Milky Way, and best seen under moonless, dark sky conditions.  The Zodiacal Light is to dim to be seen in most metropolitan areas due to light and smog pollution.

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