Space

3. A star system with two stars.
5. Very bright stars at the upper right of the H-R diagram.
6. An object whose surface gravity is so great that even electromagnetic waves, at the speed of light, can't escape it.
7. Below the main sequence in the lower part of the H-R diagram.
9. The innermost layer of the sun's atmosphere.
12. A set of dark lines that show where light has been absorbed.

1. An explosion so violent that the dying star becomes more brilliant than an entire galaxy.
2. How bright a star really is.
4. A large cloud of gas and dust spread out over a large volume of space.
8. A spinning neutron star that appears to give off strong pulses of radio waves.
10. Found just below the super giants in the H-R diagram.
11. The outermost layer of the sun's atmosphere.