Cosmic microwave background and submarine: what they have in common

1. Step 1. Cosmic microwave background — uses — Radio telescope. Detected by a radio antenna.
2. Step 2. Radio telescope — has part — Dish antenna. A parabolic antenna.
3. Step 3. Dish antenna — uses — Reflection of light. A paraboloid focuses the waves.
4. Step 4. Reflection of light — is used in — Periscope. Reflection.
5. Step 5. Periscope — is part of — Submarine. A periscope.

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