the brightness of a star as seen from Earth

a unit of distance equal to the average distance between Earth and the sun, or about 150 million kilometers

a star system with two stars

one of the rocky objects revolving around the sun that are too small and numerous to be considered planets

the middle layer of the sun’s atmosphere

the fuzzy outer layer of a comet

a loose collection of ice and dust that orbits the sun, typically in a long, narrow orbit

the outermost layer of the sun

a mysterious force that appears to be causing the expansion of the universe to accelerate

an orbit in which a satellite orbits Earth at the same rate as Earth rotates and thus stays over the same place all the time

a large, round, densely packed grouping of older stars

the observation that the farther away a galaxy is, the faster it is moving away

a region where many small objects orbit the sun and that stretches from beyond the orbit of Neptune to about 100 times Earth’s distance from the sun

a streak of light in the sky produced by the burning of a meteoroid in Earth’s atmosphere

a meteoroid that passes through the atmosphere and hits Earth’s surface

a chunk of rock or dust in space, generally smaller than an asteroid

a large cloud of gas and dust in space

the small, dense remains of a high-mass star after a supernova

a spherical region of comets that surrounds the solar system

the inner layer of the sun’s atmosphere that gives off its visible light; the sun’s surface

a huge, reddish loop of gas that protrudes from the sun’s surface, linking parts of sunspot regions

an eruption of gas from the sun’s surface that occurs when the loops in sunspot regions suddenly connect

a stream of electronically charged particles that emanates from the sun’s corona

a dark area of gas on the sun’s surface that is cooler than surrounding gases