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Why is the sky dark at night?
- red-shift (to infrared) causes far away stars to be invisible to the human eye
- universe not old enough to have stars everywhere
Why is glass transparent?
- in specific atoms where the electron energy gap is too high for photons with visible wavelengths to excite the electrons into a higher energy level, the photon is not absorbed and will pass through.
Why are there two tides per 24h on earth when there's just one moon?
- water and earth are pulled on the near side, lagging water bulge on the far side.