Important terms:

astronomical unit (AU) - a unit of distance equal to the average distance between Earth and the sun, about 150 million kilometers

ellipse - an oval shape, which may be elongated or nearly circular; the shape of the planets’ orbit

dwaf planets - an object that orbits the sun and is spherical, but has not cleared the area of its orbit

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

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

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

meteorite - a meteoroid that passes through eh atmosphere and hits Earth’s surface

nuclear fusion - The process in which two atomic nuclei combine to form a larger nucleus, forming a heavier element and releasing huge amounts of energy; the process by which energy is produced in stars

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