Structure of the universe

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Across
  1. 2. they can be made up of 10 or more clusters of galaxies.
  2. 5. a large collection of stars, gas, and dust held together by gravity.
  3. 7. The four planets that orbit nearest to the sun.
  4. 9. the distance that light travels through space in one year.
  5. 10. The four planets that orbit farthest from the sun.
  6. 14. galaxies that look like spheres or ovals and don't have arms.
  7. 16. they contain as many as thousand galaxies.
Down
  1. 1. a process that emits energy in the core of the star.
  2. 3. absorbs harmful solar radiation and other gases that keep Earth warm enough for life to exist.
  3. 4. huge spherical areas where very little matter exists.
  4. 6. galaxies that appear as splotchy irregularly shaped blobs.
  5. 8. space and all the matter and energy in it.
  6. 11. a large celestial body that is composed of gas and emits light.
  7. 12. the collection of large and small bodies that orbit our central star, the sun.
  8. 13. galaxies that are shaped like pinwheels and have a central bulge
  9. 15. a spherical body that orbits the sun.