- In a galaxy, the volume of space above and below the plane of its main structure. The halo contains old stars and globular clusters as well as gas clouds consisting mainly of neutral hydrogen. The halo contains a far lower density of matter than the main body of the galaxy, which is crammed with stars and other material.
- Atmospheric phenomenon consisting of a circular ring of light around the Sun, caused by refraction of sunlight by ice crystals high in the Earth’s atmosphere. These crystals can also form a faint second image of the Sun.
- On the screen of a CRT, such as that of a TV, an unwanted light or dark zone which surrounds an image, especially bright spots.
- synonym halation
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