Download Astronomy Unit 4 Galaxies

Name: __________________________________________
Astronomy Unit 4 Galaxies
1. A collection of millions or billions of stars held together by their gravity.
____________________
2. Our galaxy. ____________________________
3. Flattened, circular region our solar system is within. _______________________
4. Central region of the Milky Way that contains older stars. ___________________
5. Spherical region of faint stars that surrounds our galaxy. ____________________
6. First person to estimate the size of our galaxy by counting stars in all directions.
___________________________
7. This prevents us from seeing the true shape of our galaxy. __________________
8. These stars are used to estimate the distance to distant parts of our galaxy.
_________________________
9. Variable stars represent which stage in evolution of stars? ___________________
10. Low mass variable stars. _____________________________
11. High mass variable stars. _____________________________
12. Variable stars are used to estimate distance because the period of variability is related to
the star’s ______________________.
13. Harlow Shapley discovered the Sun’s true place within our galaxy by measuring variable
stars in ________________________ that surround the Milky Way.
14. The Sun is located _________________ from the center of our galaxy with the
______________.
15. The Milky Way takes approximately __________________________ years to revolve
once at the Sun’s distance from the center.
16. The closer to the center of the Milky Way, the __________________ the stars revolve
around the center.
17. These are used to “see” through the gas and dust that permeates our galaxy.
___________________________
18. At the center of our galaxy resides a __________________________________ which is
a strong radio source called _____________________________.
19. To measure the mass of our galaxy, the _____________________ of stars at the
_________________________ regions is measured.
20. The speed of stars in the outer parts of the Milky Way are moving ____________ than
they should be implying that there is _______________ mass than can be seen in the
Milky Way.
21. This mass that cannot be seen is called __________________________.
22. Galaxies are categorized based on their ________________________ in a scheme called
the _________________________________.
23. The four types of galaxies:
a. ____________________
b. ____________________
c. ____________________
d. ____________________
24. The type of galaxy the Milky Way is. _____________________________
25. Easily seen objects with luminosities that are known and are used to measure distances in
the universe are called _______________________________.
26. Galaxies tend to congregate in groups called _____________________________.
27. These groupings of galaxies themselves form larger groupings called
__________________________
28. Measuring the mass of superclusters of galaxies has led to the discovery that 90% of the
universe is composed of this. __________________________
29. Galaxies grow through collisions with other galaxies in a process known as
______________________________________.
30. Edwin Hubble observed the spectra of galaxies and noticed that the farther a galaxy is
away from us the ______________ its redshift and the ______________ it is moving
away from us.
31. The rate at which a galaxy recedes is directly proportional to its distance is known as this.
___________________________
32. Hubble’s Law implies that all galaxies are moving _________________ from us and
______________________.
33. Hubble’s Law shows us that the universe is doing this. ____________________
34. The redshift caused by the expansion of the universe. ______________________
35. Hubble’s Constant tells astronomers how _______________ the universe is expanding.
36. The approximate age of the universe determined by using Hubble’s Constant.
__________________________________
37. The distribution of galaxies in the universe is not ___________________, but clusters of
galaxies lie within structures called ___________________ which surround empty
regions called __________________.
38. Galaxies that are brighter than normal are called __________________________ and
emit most of their radiation at ________________ wavelengths.
39. The source of energy in active galaxies changes over short periods of time implying they
come from regions which are _______________ in size.
40. Explosive activity in active galaxies is often emitted in two large extended regions called
__________________________.
41. Quasi-stellar radio sources are better known as _____________________.
42. Quasars show large _________________ which means they are very
_________________, so they must be the __________________ objects in the universe.
43. The energy from active galaxies comes from _____________________________ found
at the center of these galaxies where gas is ___________________ onto it.
44. Active galaxies represent an _______________ stage in evolution of galaxies from a time
when the universe had lots of gas to accrete onto supermassive black holes.
45. Some quasars evolved to form _________________ galaxies which evolved into normal
spirals while others evolved into _______________ galaxies which evolved into elliptical
galaxies.