SpaceWorks Puzzle 16

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Across
  1. 4. A date and time selected as a fixed reference.
  2. 6. A decrease in the wavelength of photons emitted by an approaching source of light.
  3. 7. Daily or during the day.
  4. 8. A localised concentration of dense material beneath the lunar surface.
  5. 9. A measure of how much a flattened sphere differs from a perfect sphere.
Down
  1. 1. A sudden, violent burning.
  2. 2. A small, dense, dark nebula.
  3. 3. Two stars revolving about each other.
  4. 5. An instrument for photographing the solar corona.