| A | B |
|---|
| gravity | An invisible force that pulls a less massive object to a more massive object |
| orbit | the path of one object in space around another object |
| solar system | the sun and everything that revolves around the Sun |
| galaxy | a system that is made up of billions of stars, star clusters and glowing clouds of dust and gas |
| universe | all of the galaxies and the space around them; everything in space |
| nebula | a cloud of dust and gas within a galaxy |
| Big Bang Theory | the theroy that the universe was created by a huge explosion |
| trajectory | the curve that a body in space takes in orbit |
| revolution | an object spinning around another object (Earth traveling around the sun) |
| rotation | a planet spinning on its axis; an object spinning in isolation |
| geocentric | the theory that Earth is the center of our solar system; it stated that the sun revolves around the Earth |
| heliocentric | the correct theory that the sun is the center of our solar system; Earth revolves around the sun |
| Ptolemy | astronomer who came up with the first theory about the universe; geocentric theory |
| Copernicus | astronomer who challenged the geocentric theory; came up with the heliocentric theory |
| Galileo | first astronomer to use the telescope |
| lunar eclipse | an eclipse of the moon; when the moon passes into the shadow of Earth/ |
| solar Eclipse | an eclipse of the aun; when the moon passes directly between our space on Earth and the sun |
| gibbous | the moon phase when approximately 3/4 of the surface is reflcting the sun's light |
| crescent | thin curved shape of the moon when it's at its smallest |
| waning | growing smaller |
