Zodiacal Light, Australia

Imaged by Peter Frankland 2h37m after sunset at Girraween National Park, Queensland.

Image ©Peter Frankland, shown with permission.

The Zodiacal light is a soft pearly cone of light extending upwards from the direction of the sun and along the plane of Earth's orbit projected against the stars - the ecliptic.

Search for it after sunset or before sunrise. The sky must be dark for the Zodiacal light is faint, perhaps the brightness of the Milky Way.   Light polluted skies will not do. Averted vision often shows it first and then it becomes obvious to the eye. It covers a larger area of sky than expected.

Visibility strongly depends on the angle that the ecliptic makes with the local horizon. Low latitudes help. The season matters. Now is not a good time in the Northern Hemisphere because the ecliptic lies low along the horizon after sunset. In Australia it is winter and the ecliptic rises sharply from the horizon.

A disk of dust out to the orbit of Jupiter and perhaps beyond produces it. The dust grains are 0.001 to 0.3 mm across and likely originate from comets.  

The dust grains are large compared to the wavelengths of visible light and consequently scatter sunlight strongly forwards. The glow is therefore brightest near to the sun.

A fainter Zodiacal Band extends around the sky to the gegenschein or counterglow directly opposite the sun.

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