1. The theory that all matter and energy in the universe was compressed into an extremely small volume that 13 billion to 15 billion years ago exploded and began expanding in all directions.
2. Hertzsprung-Russell diagram, a graph that shows the relationship between a star's surface temperature and absolute magnitude.
3. An extremely large collection of stars held together by gravity.
4. The apparent path that the Sun sraces annually on the celestial sphere.
5. The constellations on the celestial sphere through which the ecliptic passes.
6. All of matter and energy.
7. The study of the overall structure and evolution of the universe.
8. The name given to the event thought to mark the birth of the universe.
9. The name of our galaxy and to refer to the band of light we see in the sky when we look into the plane of our galaxy.
10. Galaxies that look like flat white disks with yellowish bulges at their centers. The disks are filled with cool gas and dust, interspersed with hotter ionized gas, and usually display beautiful spiral arms.
11. A place or an obiect with extremely high density, mass and gravity that can attract everything even light cannot excape its gravity.
12. The star that represents our nearest stellar neighbor in the universe and is a red dwarf about 4.3 light-years from the Sun.