Journey from the Sun

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Across
  1. 2. a short journey
  2. 3. a colorless, odorless, flammable gas that combines chemically with oxygen to form water: the lightest of the known elements. Symbol: H; atomic weight: 1.00797; atomic number: 1; density: 0.0899 grams/liter at 0°C and 760 millimeters pressure.
  3. 5. more than one nucleus
  4. 6. a force under the influence of which objects tend to move away from each other, e.g. through having the same magnetic polarity or electric charge
  5. 9. alone
  6. 10. the process or result of joining two or more things together to form a single entity.
  7. 12. the SI base unit of thermodynamic temperature (equivalent in size to the degree Celsius), first introduced as the unit used in the Kelvin scale.
  8. 13. rays electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei.
Down
  1. 1. a particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass
  2. 3. an inert gas which is the lightest member of the noble gas series (He)
  3. 4. the property of matter and radiation which is manifest as a capacity to perform work
  4. 7. (the central and most important part of an object, movement, or group, forming the basis for its activity and growth)
  5. 8. relating to or using nuclear reactions that occur only at very high temperatures
  6. 11. strip (something) of its covering, possessions, or assets; make bare