The sun after sunset

Where can you see sunlight after the sun has set? In the zodiac or sometimes directly opposite the sun in the night sky.

Gegenschein
ESO/Y. Beletsky / CC BY

You can see the sun at night, if you know where to look. But first, let’s talk about the interplanetary dust cloud. In the space between planets, on or near to the plane around which they orbit (the ecliptic), is a huge cloud of tiny particles. They are probably the leftovers from asteroid and comet smashes out in space. Because it is concentrated along a relatively narrow band, when the sun hits them just right this interplanetary dust cloud scatters sunlight to the Earth’s night sky.

The zodiacal light runs above and below the ecliptic plane – roughly the band of the zodiac – and is visible just after sunset and just before dawn. Islamic astronomers called it the false dawn (especially relevant because of the timing of the dawn daily prayer Fajr). Most of the time its faint light is drowned out by the moon or human-generated light pollution, but if you find a place and a time dark enough the glow is quite apparent.

The gegenschein is even weirder. This light also comes from sunlight being scattered by interplanetary dust, except instead of appearing on the zodiac it appears directly opposite the sun. (At the antisolar point – which is also the point around which all rainbows appear.) Like the zodiacal light it’s very faint, but this glow is clearly visible in the right conditions.

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