Universe

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Across
  1. 3. a gravitational bound system
  2. 5. a force pulling an object to Earth
  3. 7. a pure substance
  4. 8. a small piece of matter
  5. 10. symbol is He on the periodic table
Down
  1. 1. first theory about the universe
  2. 2. atomic number 1
  3. 4. the entire range of electromagnetic radiation
  4. 6. where everything exists
  5. 9. Cosmic Microwave Background