Ch 26: The Universe

solar wind

a stream of electrically charged particles that flows from the sun outward through the solar system

sunspot

an area of gas in the sun's photosphere that is cooler than the surrounding gases

prominences

huge loops of gas that erupt from sunspot regions and extend upward from the photosphere

solar flare

a dramatic eruption on the sun's surface, usually near sunspots, that produces X-rays and send charged particles into space

light-year

the distance that light travels in a vacuum in a year, about 9.5 trillion kilometers

parallax

an apparent change in position of an object with respect to a distant background when viewed from different locations

apparent brightness

the brightness of a star as it appears from Earth

absolute brightness

a characteristic property of a star that does not depend on the star's distance from Earth

H-R diagram

the Hertzsprung-Russell diagram, a graph of the surface temperature versus absolute brightness of a sample of star

main sequence

a diagonal band on the H-R diagram, which represents about 90% of all stars

supernova

an enormous explosion in which the byproducts of a supergiant star's lifetime of fusion are flung into space

pulsar

a spinning neutron star that appears to give off strong pulses of radio waves

black hole

an object whose surface gravity is so great that not even electromagnetic waves can escape from it

constellation

a group of stars that appears to form a pattern as seen from Earth

star system

a group of two or more stars held together by gravity

galaxy

a huge group of stars, star systems, star clusters, dust, and gas bound together by gravity

quasar

enormously bright center of a distant young galaxy

red shift

a shift toward the red wavelengths of light from stars or galaxies moving away from Earth

Hubble’s Law

the direct variation of the speed at which a galaxy is moving away from Earth with is distance from Earth

big bang theory

the theory of the beginning of the universe in an instant, billions of years ago, in an enormous explosion

dark matter

matter that does not emit radiation that astronomers can detect