1. A bundle of light energy thought of as a particle but not having real mass.
3. 186,284 miles per second or 299,796 kilometers per second. (3 words)
7. Solar ______ - a very rapid release of energy from the Sun's surface.
8. Abbreviation for 21 down.
10. The negatively charged particle in the portion of an atom outside the 
    nucleus.
11. A unit of electrical current equivalent to about 6 X 1018 electrons 
    per second.
12. Earth and Jupiter are two examples of this.
13. Usually the most distant planet.
15. The regions in the magnetosphere of a planet where the magnetic field 
    lines of force have a geometrical shape like a funnel.
17. The huge region around the Sun that encloses the solar wind and its 
    magnetic field.
19. The abbreviation for a period of time encompassing parts of years 1957 
    and 1958; this marked the beginning of major cooperation in the Space 
    Age among space and Earth scientists.
22. Refers to something, usually a particle, moving at a speed near the 
    speed of light.
23.  ____-8. A NASA spacecraft launched in October 1973, in order to study 
    the space around the Earth out to about the distance of the Moon.
25. A spherical region in which a trillion or so comets are stored. (2 words)
28. An instrument that measures the strength of the magnetic field.
32. X-_____.  Light waves with wavelengths shorter than those of ultraviolet
    light but longer than those of gamma rays.
34. The abbreviation for part of a worldwide program of scientific space 
    studies.
35. The abbreviation for the amount of energy needed to move an electron 
    through a one volt electrical potential.
36. A fragile body of ice and dust in orbit around the Sun.
37. The last giant outer planet, measured by distance from the Sun, of 
    the four giant outer planets.

1. The boundary of the heliosphere.
3. A series of disturbances on a planet causing auroras (in Earth's case) 
   at lower latitudes.
4. Atoms of one type which cannot be broken down further into a more 
   fundamental type by chemical reactions.
5. Anything having to do with the Earth.
6. The atom's discrete energy level. (2 words)
9. The process of emitting visible light after a gas has absorbed 
   ultraviolet light (or other short wavelength light).
11. The gas envelope that surrounds a body in space which is held to that 
    body by gravity.
13. A spacecraft, launched in 1995, which is orbiting above the Earth's 
    north and south poles.
14. The path or trajectory of a body in space.
16. A thing appearing as an abrupt change in pressure and temperature in 
    a fluid (or gas) in which its speed is faster than some signal speed 
    in the fluid.
18. The planet upon which we live.
20. Very high frequency electromagnetic waves with very small wavelengths. 
    (2 words)
21. The mass of a thousand grams.
24. The natural satellites orbiting around planets.
26. The layer of gas and dust (100's of thousands of kilometers across)
    surrounding a comet nucleus.
27. A very common structure of magnetic field lines in nature.
29. The fourth planet from our Sun.
30. The abbreviation for 11 across.
31. The abbreviation for a 3-axis coordinate system, with Earth at 
    its center. 
33. The abbreviation for bundles or clouds of electrically charged gas 
    ejected from near the Sun's surface.