Space telescope and gas lamp: what they have in common

1. Step 1. Space telescope — has part — Solar panel. Solar panels.
2. Step 2. Solar panel — uses — Photovoltaic effect. The photoelectric effect in a semiconductor.
3. Step 3. Photovoltaic effect — is used in — Photoresistor. Photoconductivity.
4. Step 4. Photoresistor — is part of — Street light. Switching on at dusk.
5. Step 5. Street light — evolved from — Gas lamp. Gas lamps.

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