Unit #1: The Universe

4. | Leftover heat energy from the Big Bang |
5. | The part of the electromagnetic spectrum humans can see |
10. | A shift of light toward the red end of the spectrum when objects move away |
14. | Matter that cannot be seen directly but affects objects through gravity |
15. | An element formed shortly after the Big Bang |
17. | A huge group of stars, gas, and dust held together by gravity |
19. | All forms of electromagnetic radiation, including visible light, radio waves, and X-rays |
20. | A galaxy with spiral arms rotating around a center |
21. | The astronomer who discovered galaxies beyond the Milky Way and evidence of expansion |
22. | A rounded or oval-shaped galaxy mostly made of older stars |
23. | The theory that the universe began from a hot, dense point and expanded |
24. | The observation that galaxies are moving farther apart over time |
26. | The number of waves passing a point each second |
29. | Dark lines formed when atoms absorb specific wavelengths of light |

1. | A region in space where gravity is so strong that light cannot escape |
2. | Dark absorption lines seen in the Sun’s spectrum |
3. | A hypothetical collapse of the universe back into a single point |
6. | A complete range of colors without gaps |
7. | The distance between matching parts of a wave |
8. | A mysterious energy believed to cause the universe’s expansion to speed up |
9. | Everything that exists, including space, time, matter, and energy |
11. | A small galaxy containing fewer stars than large galaxies |
12. | The lightest and most common element in the universe |
13. | A galaxy with no clear shape |
16. | The change in wave frequency caused by motion between objects |
18. | Bright lines produced when atoms release energy |
20. | The range of colors or wavelengths produced when light is separated |
25. | A transparent object that separates light into colors |
27. | The idea that galaxies farther away move away faster |
28. | The distance light travels in one year |