Outer Space

3. a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
7. the movement of an object around another object
9. the spinning of a planet on its axis
12. an object that orbits a star, is large enough to have become rounded by its own gravity, and has cleared the area of its orbit.
16. period of time when the sun shines at a maximum on one hemisphere and a minimum on the other
18. one of the highly dense planets nearest to the sun that have a solid surface; Mercury, Venus, Mars, and Earth
19. a thin disk of small ice and rock particles surrounding a planet.
20. the distance light travels in one year; about 6 trillion miles
21. dark area of gas on the sun's surface that is cooler than surrounding gases.
22. Space and all the matter and energy in it

1. planetary bodies made mainly of gases and no solid surface, including Jupiter, Saturn, Uranus, and Neptune
2. path of one object around a more massive object due to gravity
4. the collection of planets and their moons in orbit around a sun, together with smaller bodies in the form of asteroids, meteoroids, and comets.
5. a pattern of climate and weather changes that occur during a year
6. A force of attraction between objects that is due to their masses.
8. rise and fall of the Earth's water due to the pull of the moon's gravity
10. a round depression formed on the surface of a planet, moon, or other space object by the impact of a meteorite
11. period of time when the sun shines equally on the northern and southern hemispheres
13. unit of length used for distances within the solar system; 1 AU = about 93 million miles
14. large spiral galaxy that is home to Earth and the rest of our solar system, and about a trillion stars.
15. the outermost layer of the sun's atmosphere
17. elongated circle, or oval shape; the shape of the planets orbit.