Across
- 1. the celestial firmament
- 4. transparent substance used to change the convergence of light
- 7. dealing with the phenomena of visible and invisible light
- 8. changing the direction of light
- 9. casting back a light to show an image
- 10. a grouping of stars with a name
Down
- 1. a natural body that revolves around a planet
- 2. the boundary between the earth and sky
- 3. optical instrument used to make distant objects appear larger
- 5. a position on a line from one point to another
- 6. polished metal or glass with a metallic backing; reflects light