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Astronomy & Telescopes Glossary - B
Bailey's Beads - Bead-like lights that appear just before and after totality during a solar eclipse. Bailey's beads are caused by light shining through valleys on the edge of the moon.
Barlow lens - A lens placed in front of a telescope eyepiece that increases focal length and magnification.
Barred spiral galaxy (SB) - A spiral galaxy whose center is elongated or bar-shaped.
Bayer system - A classification system in constellations where every star is assigned a Greek letter in order of decreasing brightness. The brightest star in a constellation is alpha, the second-brightest is beta, the third is gamma, and so on.
Binary Star - Two (or more) stars that rotate around a common center of mass.
Bino-viewer - An optical device that splits the beam of light from a telescope into two parts, so you can observe objects with both eyes at once.
Black Drop Effect - An optical effect that happens in a transit of Venus, when Venus just travels in front of the solar disk. The light from the Sun is refracted by the dense atmosphere of Venus, making it look stretched-out.
Blue moon - When a single month has two full moons, the second full moon is called a Blue Moon.
Bolide - A meteor, asteroid or comet that hits the Earth (or other planet) and explodes.