Halo is a luminous ring or a disk of light that surrounds an object. Halos commonly appear in Christian religious art as a symbol of saintliness or divinity. In many religious paintings created since the 400’s, Jesus Christ and the Virgin Mary, as well as the angels and saints, have been portrayed with a shining circle around the head. The golden or jeweled crowns worn by royalty were originally modeled after the sacred halo. Such a crown was meant to signify the wearer’s “divine right” to rule.
The term halo is also used in connection with various natural phenomena. The pale ring of light that occasionally appears around the sun or moon is called a halo. Such rings are most often seen during winter. They appear when light rays are refracted (bent) by ice crystals in the earth’s upper atmosphere.
Another type of halo is the sphere of stars that surrounds a spiral or elliptical galaxy (see Galaxy ). This galactic halo consists of older stars containing few elements heavier than hydrogen and helium. This type of halo may extend hundreds of thousands of light-years from the center of a galaxy. Astronomers also speak of a halo of comets surrounding the solar system. These comets all orbit the sun at a distance of about 9.3 trillion miles (15 trillion kilometers). Many of the comets themselves are enveloped by a halo made of hydrogen gas. This halo forms when a comet travels close enough to the sun for the frozen methane and ammonia in the comet’s head to change directly into gas.
