Milky Way

2. a unit of distance equal to 1000 pc or 3260 ly
3. orbital motion in accord with kepler's laws of planetary motion
8. stars that are poor in atoms heavier than helium
10. the process by which the birth of stars compresses the surrounding gas clouds and triggers the formation of more stars
13. the powerful radio source located at the center of the galaxy
14. in astronomical usage, any atom heavier than helium
15. a material confined to the plane of the galaxy
18. the relation between period and pulsation
19. the spherical region of a spiral galaxy containing a thin scattering of stars

1. objects used to map the spiral arms
4. the rate at which a star moves across the sky
5. stars rich in atoms heavier than helium
6. a graph of orbital velocity versus radius in the disk of a galaxy
7. the spheriodal cloud of stars at the center of most spiral galaxies
9. a region of hr diagram in which stars are unstable to pulsation
11. variable star with a period of 12 to 24 hours
12. non luminous material that is detected only by its gravitational influence
16. the production of elements heavier than helium by the fusion of atomic nuclei in stars and during supernovae explosions
17. a variable star with a period of 1 to 60 days