1. Stars, Galaxies, and the Universe
Chapter 2

2. Stars Section 1 Vocabulary Spectrum Apparent Magnitude
Absolute Magnitude
Light-Year
Parallax

3. Color of Stars Red and Yellow Blue Blue flame hotter than yellow flame
Cool
Blue
Warm
Blue flame hotter than yellow flame
Stars different color
Betelgeuse-Red
Rigel-Blue

4. Composition of Slides Different elements of gases Inner Layers
Very dense and hot
Outer Layers (Atmosphere)
Cool Gases
Elements in a star’s atmosphere absorb some of the light that radiates from the star.
Different wavelengths- different elements

5. The Colors of Light
The band of color produced when white light passes through a spectrum
Millions of colors- rainbow
Continuous spectrum- shows all color
Glowing wire
Spectrograph
Break star’s light into a spectrum
Composition and Temperature
Neon sign

6. Making and ID
Neon Sign
Emission lines-lines that are made when certain wavelengths of light, or colors, are given off by hot gases.
When an element emits light, only some colors in the spectrum show up, while other colors are missing.
Unique set of bright emission lines
Fingerprints

7. Trapping the Light-Cosmic Detective Work
Stars produce spectrums
Dark emission lines
A star’s atmosphere absorbs certain colors of light in the spectrum, which causes black lines to appear.

8. Identifying Elements Using Dark Lines
Absorption Spectrum- produced when light from a hot solid or dense gas passes through a cooler gas
A star gives off an absorption spectrum because a star’s atmosphere is cooler than the inner layers of the star.
The black lines represent places where less light gets through.

9. Identifying Elements Using Dark Lines
The pattern of lines in a star’s absorption spectrum shows some of the elements that are in the star’s atmosphere.
One element-Easy
More than one element- hard

10. Classifying Stars
1800’s- astronomers started to collect and classify the spectra of many stars.
Classified according to the elements
Classified in the wrong order

11. Differences in in Temperature
How hot
Temperature differences between stars result in color differences that you can see
O stars
Blue
Hottest
Highest temperature to lowest temperature

12. Differences in Brightness
Early astronomers created a system to classify stars based on their brightness.
First-magnitude –brightest stars
Sixth-magnitude – dimmest stars
Some stars are too dim to see
Added to the old system
Positive numbers- dimmer stars

13. Apparent Magnitude The brightness of a star as seen from Earth
Depends on the square of the ratio between the light and the light meter
Some stars are brighter than other stars because of their size or energy output, not because of their distance from Earth.

14. Absolute Magnitude
The brightness a star would have at a distance of 32.6 light years away
If all stars were the same distance away, their absolute magnitudes would be the same as their apparent magnitudes.
Sun-
Absolute Magnitude
+4.8
Ordinary
Apparent Magnitude
-26.8
Brightest object in the sky

16. Distance to the Stars
Light-Years to measure distances from Earth to the stars
Stars near the Earth seem to move, while more distant stars seem to stay in one place as earth revolves around the sun.
Parallax-an apparent shift in the position of an object when viewed from different locations
Location of the nearer star seems to shift in relation to the pattern of more distant stars
Only seen through telescopes
Parallax and simple trigonometry to find actual distances

17. Motions of the Stars Daytime and Nighttime caused by rotation
Each season-faces different parts of the sky
Different set of constellations

18. The Apparent Motion of Stars
Sun appears to move across the sky
Look long enough, the star appear to move
Polaris
Appear to make one complete circle around Polaris

19. The Actual Motion of Stars
Moving in space
Distance makes it hard to see
Star pattern slowly change their shape

20. The Life Cycle of Stars Section 2 Vocabulary Red Giant White Dwarf
H-R Diagram
Main Sequence
Supernova
Neutron Star
Pulsar
Black Hole

21. The beginning and End of Stars
First Stage- ball of gas and dust
Gravity pulls it together into a sphere
More Dense- Hotter
Nuclear Fusion- Hydrogen changes to Helium
Older-lose some materials
Materials returns to space
Forms new stars

22. Different Types of Stars
Stars can be classified:
Mass
Brightness
Color
Temperature
Spectrum
Age
Types of stars:
Main-sequence
Giants
Supergiants
White Dwarf
Classifications can change.

23. Main-Sequence Stars Second and Longest Stage
Energy is generated in the core of the star as hydrogen atoms fuse into helium atoms
Releases an enormous amount of energy

24. Giants and Supergiants
Third stage of life
a large, reddish star late in its life cycle
Loss of hydrogen causes center of the star to shrink
Atmosphere of the star grows very large and cools
Red giants- 10 times bigger than the sun
Supergiants- 100 times bigger than the sun

25. White Dwarfs Final Stages- Same mass as the sun or smaller
A small, hot, dim star that is the leftover center of an old star
No hydrogen left and can no longer generate energy by fusing hydrogen atoms into helium atoms
Can shine billions of years before cooled

26. A Tool for Studying Stars
1911-Hertzsprung compared the brightness and the temperature of stars on a graph
1913-Russell made some similar graphs
Different data- same results
Hertzsprung –Russell Diagram H-R Diagram
Tool for studying the lives of stars

27. Reading the H-R Diagram
Temperature is on the bottom
Absolute Magnitude is on the left side
Blue stars on the left
Red stars on the right
Bright stars on the top
Dim stars on the bottom
Main sequence
Most of the lifetime

29. When Stars Get Old Do not stay on the main sequence forever
Average stars- red giants then white dwarfs
Stars that are larger than the sun- may explode
Supernovas
Neutron stars
Pulsars
Black holes

30. Supernovas Blue stars May Explode
use their hydrogen much faster than stars like the sun
generate more energy that stars like the sun
Do not have long lives
May Explode
Supernova
Brighter than an entire galaxy for several days

31. Neutron Stars and Pulsars
After a supernova
Material in the center are squeezed together to form a new star
About two times the mass of the sun
The particles are forced together to form neutrons
Pulsars
Neutron Star spinning
Sends out a beam of radiation that spins rapidly
Beam is detected on Earth by radio telescopes as rapid clicks or pulses

32. Black Holes
The leftovers of a supernova are so massive that they collapse to form a black hole
Do not give off light, finding them is difficult
If a star is nearby, some gas or dust from the star will spiral into the black hole and give off X-rays

33. Galaxies Section 3 Vocabulary Galaxy Nebula Globular Cluster
Open Cluster
Quasar

34. Types of Galaxies Many Different Types 1920’s-classify galaxies
By shape
Edwin Hubble
Still use the galaxy classification

35. Spiral Galaxies Bulge at the center Spiral Arms
Gas, Dust, and New Stars
Denser Regions of Gas and Dust

36. The Milky Way Hard to tell what type of galaxy
Gas, dust, and stars keep astronomers from having a good view
They think it is a spiral galaxy.

37. Elliptical Galaxies
One-third of all galaxies are massive blobs of stars.
Elliptical Galaxies- bright centers and very little dust and gas
Contain mostly old stars
No to little free flowing gas
Giant elliptical galaxies
Dwarf elliptical galaxies

38. Irregular Galaxies Group of leftovers- “irregulars”
Do not fit into any other class
Shape-irregular
Large Magellanic Cloud
close companions of large spiral galaxies

39. Contents of Galaxies
Composed of billions of stars and some planetary systems
Form large features
Gas clouds
Star clusters

40. Gas Clouds Nebula Large clouds of dust and gas Some Glow
others absorb light and hide stars
Others reflect starlight and produce some amazing images
Some are regions that form new stars
Spiral-nebulas
Elliptical-very few

41. Star Clusters Globular clusters- groups of older stars
Up to one million stars
Located in a spherical halo that surrounds spiral galaxies
Common near giant elliptical galaxies
Open clusters-closely grouped stars
Located along the spiral disk of a galaxy
Newly formed-many bright blue stars
Few hundred to a few thousand stars

42. Origin of Galaxies Observing objects far away
Takes time for light to travel through space, looking through a telescope is like looking back in time
Shows what early galaxies looked like
How they change over time and what caused them to form

43. Formation of the Universe
Section 4 Vocabulary
Cosmology
Big Bang Theory

44. Raisin-Bread Model Imagine a loaf of bread before its baked
Each raisin is a certain distance apart
As the dough rises, it expands and all of the raisins begin to move apart
Other raisins are moving away from it
The universe is expanding
Raisins as galaxies
Galaxies move apart

45. The Big Bang Theory What it would look like in reverse
It look like it is contracting.
All matter would come together at a single point
Squeezed into one small space

46. A Tremendous Explosion
Big Bang Theory
13.7 billion years ago- all the contents of the universe was compressed under extreme pressure, temperature, and density in a very tiny spot
Rapidly expanded
Matter began to come together and form galaxies

48. Cosmic Background Radiation
1964- twos scientists using a huge antenna accidentally found radiation coming from all directions in space
Cosmic background radiation
Kitchen oven
Big Bang Theory- the thermal energy from the original explosion was distributed in every direction as the universe expanded
Now fills all of space

49. Structure of the Universe
Universe stretches out farther than astronomers can see with their advanced instruments
Not simply scattered through the universe in a random pattern
Has structure

50. A Cosmic Repetition Part of a larger system
Cluster or group of galaxies can be made up of smaller star clusters and galaxies
Can include planetary systems
Other planets can be detected in orbit around other stars
common

51. How Old Is the Universe?
One Way scientists can calculate the age of the universe is to measure the distance from Earth to various galaxies
Estimate the age of the universe and predict its expansion
To calculate the ages of old, nearby stars

53. A Forever Expanding Universe
As they move farther apart they get older and stop forming stars
The expansion of the universe depends on how much matter the universe contains
Gravity could eventually stop expanding
Eventually start collapsing
Not enough matter
Will continue to expand forever
cold and dark