Answer:
Astronomical unit
a unit of measurement equal to 149.6 million kilometers, the mean distance from the center of the earth to the center of the sun.
Light year
a unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 1012 km (nearly 6 trillion miles).
Planet
a celestial body moving in an elliptical orbit around a star.
Solar system
the collection of eight planets and their moons in orbit around the sun, together with smaller bodies in the form of asteroids, meteoroids, and comets. The planets of the solar system are (in order of distance from the sun) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Galaxy
a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
Universe
all existing matter and space considered as a whole; the cosmos. The universe is believed to be at least 10 billion light years in diameter and contains a vast number of galaxies; it has been expanding since its creation in the Big Bang about 13 billion years ago.
Star
a fixed luminous point in the night sky which is a large, remote incandescent body like the sun.
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