1															2
																	3
4
																				5
	6		7													8			9
10													11
							12
																													13
											14															15
																		16
17											18
													19
											20
																	21
																	22

Across 3. M31, the Milky Way's nearest galactic neighbor, separated by 2.5 million light years 4. large grouping of stars consisting of central galactic bulge surrounded by spiral arms, flat disk shaped, our Milky Way & Andromeda 9. gaseous clouds in space with matter depressed in free-falling molecules 10. a distance-measurement technique, luminosity changes with time, some erratically & others regularly, characteristic light curves 12. dark nebulae keep you from seeing most stars located in the center, many clusters found here 17. gargantuan collection of stellar & interstellar matter - stars, dust, gas, neutron stars, black holes - held together by own gravity 18. pulsating variable star, used to determine distances to globular clusters, periods of less than a day 19. visible light cannot penetrate these clouds 20. young, in spiral arms, hot & bright 21. located in the suburbs of our galaxy, 30,000 ly from central region 22. region of a galaxy extending far above and below where independent stars reside

Down 1. region of EM spectrum just outside visible range, shorter wavelengths than color red 2. discovered by Henrietta Leavitt, the correlation between average luminosity & pulsation period 5. pulsating variable star, WW Cygni, a period of several days 6. region of electromagnetic spectrum with longest wave length, special instruments needed to detect 7. most easily seen in the Northern Hemisphere during our summer 8. found in the halo of the galaxy, thousands & millions of tightly bound stars 11. contain luminous stars, open star clusters & emission nebulae, all found in star formation regions & all young 13. starts from compressed gas and dust entering a density wave 14. 18th Century English astronomer, estimated size and shape of our Galaxy 15. immense circular, flattened region containing most of the G luminous stars & interstellar matter 16. old, low temperature