| Answer | Crossword Clue |
|---|---|
| RAYS | Travelers at the speed of light |
| BEAM | It travels at the speed of light |
| GAMMARAYS | Radioactive emissions moving at the speed of light |
| CONSTANT | Like the speed of light |
| OUCAVNI | How the speed of light is measured |
| INVACUO | Where the speed of light is constant |
