Glossary term: Zodiacal Light

Description: Within the Solar System, planets and other bodies mostly orbit within the plane of the ecliptic. Interplanetary dust in our cosmic neighborhood is also concentrated near that plane. Some light from the Sun is reflected by those interplanetary dust grains in the ecliptic towards Earth. In principle, that produces a faint glowing ribbon across the night sky, along the Zodiac – the region in the night sky close to the ecliptic. In practice, that glow is only visible with the naked eye to the east shortly before sunrise or to the west shortly after sunset, only close to the horizon, and only from a naturally dark observing location. That visible part of the glow is the zodiacal light: a diffuse glowing region shaped like a rounded, elongated triangle that reaches from the horizon a short way along the ecliptic.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

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A smooth, diffuse glow extends from the horizon towards the upper left. In the top left there is a pair of two bright stars

Zodiacal Light over GTC Observatory

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   Taken from La Palma, Canary Islands, in May 2022, this image captures the Zodiacal light, three prominent constellations (Gemini, Cancer and Auriga), and the Beehive Cluster, which appears as a small nebulosity to the unaided eye under dark skies. The Zodiacal light is a triangular white glow stretching along the ecliptic that is visible here at the western horizon shortly after sunset.The Canary Islands were considered the westernmost land of the inhabited world by the ancient Greeks. The dim shimmer in the Zodiac might have inspired the Greek philosopher Plato to think that the Sun leaves a trace of sunny glitter in its wake, and that the current path of the Sun, the ecliptic, has not always been its path. Plato believed that the Milky Way was a former path of the Sun and that its bright clouds are sparks of the Sun’s glory left behind. Today, we know that these two phenomena in the sky have different causes; while the Zodiacal light is really caused by reflection of sunlight from very tiny dust particles in the plane of the ecliptic, the Milky Way consists of billions of stars. The Zodiacal light is a smooth cone of light from the horizon upwards, while the Milky Way crosses the whole sky and also includes dark clouds. The Zodiac is described by Indigenous Australians as the Dreaming Road, and the Zodiacal light is a celestial rope connecting Venus to the Sun. The two bright stars in the top-left of the image are Castor (the bluish star) and Pollux (the whitish star), which are part of the constellation Gemini, the Twins. The two bright stars towards the bottom-right of the image are Menkalinan (the dimmer one) and Capella (the brighter one), which are part of the constellation Auriga, the Charioteer. The Wergaia people of Western Victoria in Australia see Castor and Pollux as brothers who hunt the kangaroo Purra in their stories. This has coincidental similarities to the Babylonian story, where they are considered two strong gods of the Netherworld, depicted with weapons. The Greco-Roman myth of the twins describes them as two brothers who accompanied the first ocean sailor, Jason, on voyages with the The Ship, Argo. A similar myth exists in the Blackfoot traditions of the First Nations people of Canada and the USA, where they are considered the two brothers Ashes Chief and Struck-behind.
Credit: Amirreza Kamkar/IAU OAE

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