1. Stars, Galaxies & The Electromagnetic Spectrum
4.f. Describe the hierarchical structure (stars, cluster, galaxies, galactic clusters) of the universe & examine the expanding universe to include its age & history & the modern techniques (e.g. radio, infrared, ultraviolet & x-ray astronomy) used to measure objects & distances in the universe. (DOK 2)
2.e. Contrast various components of the electromagnetic spectrum (e.g. infrared, visible light, ultraviolet) & predict their impacts on living things. (DOK 2)
Stars, Galaxies & The Electromagnetic Spectrum

2. Vocabulary Words – Chapter 4 & 21
Electromagnetic wave
Electromagnetic radiation
Electromagnetic spectrum
Radio waves
Microwaves
Radar
Infrared rays
Visible light
Ultraviolet rays
X-rays
Gamma rays
Incandescent light
wavelength
Spectrum
Constellation
Light-year
Apparent brightness
Absolute brightness
Spectrograph
Parallax
Hertzsprung-Russell diagram
Main sequence
Open cluster
Globular cluster
Galaxy
Milky Way
Universe

3. Definitions
Electromagnetic wave – transverse waves that transfer electrical and magnetic energy
Electromagnetic radiation – the energy transferred through space by electromagnetic waves
Electromagnetic spectrum – the complete range of electromagnetic waves placed in order of increasing frequency
Radio waves – electromagnetic waves with the longest wavelengths and lowest frequencies
Microwaves – radio waves with the shortest wavelengths and the highest frequencies
Radar – a system that uses reflected radio waves to detect objects and measure their distance and speed
Infrared rays – electromagnetic waves with wavelengths shorter than radio waves, but longer than visible light

4. Definitions
Visible light – electromagnetic waves that are visible to the human eye
Ultraviolet rays – electromagnetic waves with wavelengths shorter than visible light, but longer than x-rays
X-rays – electromagnetic waves with wavelengths shorter than ultraviolet rays, but longer than gamma rays
Gamma rays – electromagnetic waves with the shortest wavelengths and highest frequencies
Incandescent light – light bulb that glows when a filament inside it gets white hot
Wavelength – the distance between the crest of one wave and the crest of the next wave
Spectrum – the range of wavelengths of electromagnetic waves
Constellation – an imaginary pattern of stars in the sky

5. Definitions
Light-year – the distance that light travels in one year, about 9.5 trillion kilometers
Apparent brightness – the brightness of a star as seen from Earth
Absolute brightness – the brightness a star would have if it were at a standard distance from Earth
Spectrograph – an instrument that separates light into colors and makes an image of the resulting spectrum
Parallax – the apparent change in position of an object when seen from different places
Hertzsprung-Russell diagram – a graph relating the surface temperatures and absolute brightness of stars
Main sequence – a diagonal area on a H-R diagram that includes more than 90% of all stars

6. Definitions
Open cluster – a star cluster that has a loose, disorganized appearance and contains no more than a few stars
Globular cluster – a large, round, densely-packed grouping of older stars
Galaxy – a huge group of single stars, star systems, star clusters, dust and gas bound together by gravity
Milky Way – a spiral galaxy that contains our solar system
Universe – all of space and everything in it

7. The Electromagnetic Spectrum
Objective 2.e.

8. The electromagnetic spectrum (EM spectrum)
The complete range of electromagnetic waves placed in order of increasing frequency
Made up of radio waves, infrared rays, visible light, UV rays, x-rays, and gamma rays

9. Electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light

10. Speed = wavelength x frequency
Wavelength – the distance between the crest of one wave and the crest of the next wave
Frequency – the number of occurrences of a repeating event per unit of time
The speed of all electromagnetic waves is the same
Wavelength decreases, frequency increases
Wavelength increases, frequency decreases

11. Waves with long wavelengths have lower frequencies
Waves with shorter wavelengths have higher frequencies
The amount of energy carried by an electromagnetic wave increases with frequency
The higher the frequency of a wave, the higher its energy

12. the higher the
frequency of a
wave, the
higher its energy

13. Parts of the EM Spectrum
Radio waves
Electromagnetic waves with the longest wavelengths and lowest frequencies
Includes:
Broadcast waves
Radio and TV waves
Longer wavelengths
Microwaves
Shorter wavelengths
Cellular devices
Radar

14. Parts of the EM Spectrum
Infrared rays
Electromagnetic waves with wavelengths shorter than those of radio waves
If you turn on a burner on an electric stove, you can feel it warm up before the heating element starts to glow
The invisible heat you feel is infrared rays
Have a higher frequency than radio waves, so they have more energy
You feel the energy as heat
Examples:
Heat lamps
Infrared cameras
Thermograms

15. Visible light
Shorter wavelengths and higher frequencies than infrared rays
Electromagnetic waves that you can see
Only make up a small part of the EM Spectrum

16. Visible light
Visible light waves with the longest wavelengths appear red
As the wavelengths decrease, you can see other colors of light
The shortest wavelengths of visible light appear violet in color
Colors in order of longest wavelength to shortest wavelength
Red, orange, yellow, green, blue, violet

17. Visible light
Visible light that appears white is actually a mixture of many colors

18. Ultraviolet rays (UV rays)
Electromagnetic waves with wavelengths just shorter than those of visible light
Higher frequencies than visible light, so they carry more energy
The energy of UV rays is great enough to damage or kill living cells
UV lamps are often used to kill bacteria on hospital equipment

19. UV rays Small doses of UV rays are useful
Example: UV rays cause skin cells to produce vitamin D, which is needed for healthy bones and teeth
However, too much exposure to UV rays is dangerous
UV rays can burn your skin, cause skin cancer, and damage your eyes
Wear sunscreen to block UV rays

20. X-rays
Electromagnetic waves with wavelengths just shorter than those of UV rays
Higher frequency than UV rays, so they carry more energy
They can penetrate through most matter

21. X-rays Bone and lead are considered dense matter
They absorb x-rays and do not allow them to pass through
X-rays are used to make images of bones inside the body or of teeth

22. X-rays Too much exposure to x-rays can cause cancer
If you’ve ever had a dental x-ray, you’ll remember that the dentist gave you a lead apron to wear
The lead prevents the x-ray from reaching your body
X-rays are also used in industry and engineering

23. Gamma rays
Electromagnetic waves with the shortest wavelengths and highest frequencies
Greatest amount of energy
Some radioactive substances and certain nuclear reactions produce gamma rays
Can be used to kill cancer cells inside the body
Some objects in space give off bursts of gamma rays, but they are blocked by Earth’s atmosphere

24. Discussion Questions
Why are shorter wavelengths more damaging than longer wavelengths
Does exposure to any type of energy on the EM Spectrum cause cellular damage? Why or why not?
Which wavelengths are visible to the human eye and which are not?
Which part of the EM Spectrum has the shortest wavelengths?
What is the order of visible light from longest wavelengths to shortest?
How are wavelengths and frequency related?
How are frequency and the amount of energy present related?
What is the best way to avoid skin cancer?
How do we feel the energy of infrared rays?

25. The Universe
4.f. describe the hierarchical structure of the universe and examine the expanding universe to include its age and history and the modern techniques used to measure objects and distances in the universe (DOK 2)

26. Hierarchical structure of the universe
Smallest to largest
Stars
Clusters
Galaxies
Galactic clusters

27. Classifying stars Characteristics used to classify stars include:
Color
Temperature
Size
Composition
Brightness

28. Color and temperature
If you look at the night sky, you can see slight differences in the colors of the stars
Example:
Betelgeuse (BAY tul jooz), the bright star in Orion’s shoulder, looks reddish
Rigel, the star in Orion’s heel, is blue-white

31. Color and temperature
Like hot objects on Earth, a star’s color reveals its surface temperature
If you watch a toaster heat up, you can see the wires glow red-hot
The wires inside a light bulb are even hotter and glow white
Similarly, the coolest stars appear reddish in the sky
The hottest stars appear bluish
Medium temperature stars appear yellow

32. Size
When you look at stars in the sky, they all appear to be points of light of the same size
Many stars are about the same size of the sun, which is a medium sized star
Some stars are much larger than the sun
Very large stars are called giant stars or supergiant stars
Giant stars are 10 to 100 times larger than the sun

33. Size
If the supergiant star Betelgeuse were located where our sun is, it would be as far out as Jupiter
Betelgeuse is 420 million kilometers in diameter

34. Size Most stars are much smaller than the sun
White dwarf stars are about the size of Earth
Neutron stars are even smaller
20 kilometers in diameter

35. Composition
Astronomers use spectrographs to determine the elements found in stars
A spectrograph is a device that breaks light into colors and produces an image of the resulting spectrum

36. Brightness of stars Depends upon both its size and temperature
The hotter the star, the brighter it shines
The bigger the star, the brighter it shines
How bright a star looks from Earth depends on both its distance from Earth and how bright the star truly is

37. Brightness of a star
Because of this, the brightness of a star can be described in 2 ways:
Apparent brightness
Absolute brightness

38. Apparent brightness A star’s brightness as seen from Earth
Astronomers can measure apparent brightness fairly easily using electronic devices
However, astronomers can’t tell how much light a star gives off just from the apparent brightness

39. Apparent brightness
Just as a flashlight looks brighter the closer it is to you, a star looks brighter the closer it is to Earth
Example: the sun looks very bright
This does not mean the sun gives off more light than all other stars
The sun looks so bright simply because it is so close
In reality, the sun is a star of only average brightness

40. Apparent brightness

41. Absolute brightness
The brightness the star would have if it were at a standard distance from Earth

42. Measuring distances to stars
Imagine that you could travel to the stars at the speed of light (300,00 km/s)
To travel from Earth to the sun would take about 8 minutes!
The next nearest star, Proxima Centauri, is much farther away
A trip there at the speed of light would take 4.2 years!

43. The light-year
Distances on Earth’s surface are often measured in kilometers
However, distances to the stars are so large that kilometers are not very practical
Astronomers use a unit called a light year to measure distances between the stars

44. A light-year In space, light travels at a speed of about 300,000km/s
A light-year is the distance that light travels in one year
9.5 million million kilometers
A light-year is a unit of distance, NOT TIME!

45. Clusters Many stars belong to larger groupings called clusters
There are 2 types of clusters
Open clusters
Globular clusters

46. Open Clusters
Have a loose disorganized appearance and contain no more than a few thousand stars
They often contain many bright supergiants and much gas and dust

47. Globular clusters Large grouping of older stars
Are round and densely packed with stars
Some may contain more than a million stars

48. Galaxies
A huge group of singe stars, star systems, star clusters, dust and gas bound together by gravity
There are billions of galaxies in the universe
The largest galaxies have more than a trillion stars
Significantly larger than our solar system
Astronomers classify most galaxies into the following types:
Spiral
Elliptical
irregular

49. Spiral galaxies
Galaxies that have a bulge in the middle and arms that spiral outward, like pinwheels.
The spiral arms contain many bright, young stars as well as gas and dust
Most new stars in spiral galaxies form in these spiral arms
Relatively few new stars are forming in the central bulge

50. Spiral galaxies

51. The Milky Way
Our solar system is located in a spiral galaxy called the Milky Way
The center of the galaxy is about 25,000 light-years away

52. Galactic clusters
A structure that consists of hundreds of galaxies bound by gravity
Hold the greatest number of stars in the universe
Are the largest known gravitationally bound objects in the universe

53. The Universe, The Milky Way, & Our Solar System

54. Sequence from smallest to largest
Our solar system
The Milky Way
The universe

55. Our Solar System Our solar system includes:
The sun – center of our solar system
Planets
Belts of rock, ice and dust

56. The Milky Way
name derives from its appearance as a dim "milky" glowing band arching across the night sky
Contains our solar system
Contains about 200 billion stars
Almost everything that we can see in the sky belongs to the Milky Way
We are located on one of its spiral arms out towards the edge

57. The Milky Way

58. The Universe All of space and everything in it ENORMOUS!
Almost beyond imagination
Older than our solar system and the Milky Way

59. Is the universe expanding?

60. The expanding universe
Most astronomers believe the universe is expanding in size
Edwin Hubble studied the spectrums of many galaxies at various distances from Earth
By examining a galaxy’s spectrum, Hubble could tell how fast the galaxy is moving and whether it is moving toward our galaxy or away from it
Hubble discovered that, with the exception of a few nearby galaxies, all galaxies are moving away from us and from each other

61. The expanding universe
Hubble found that there is a relationship between the distance to a galaxy and its speed
Hubble’s law states that the further away a galaxy is, the faster it is moving away from us.

62. The expanding universe

63. How can we tell if a star/galaxy is moving toward or away from us?

64. Red shift or blue shift? Red shift
When an object is moving away, it appears red in color
The wavelengths increase and the color SHIFTS towards the red end of the spectrum
Giving the star a reddish color

65. Blue shift
When an object is moving toward our galaxy, it appears blue in color
The wavelengths decrease and this SHIFTS the color from the red end of the spectrum to the blue end
Giving the star a bluish color

66. Cosmic background radiation
Leftover thermal energy that is distributed in every direction as the universe expands

67. Age of the universe
Since astronomers can measure approximately how fast the universe is expanding now, the can infer how long it has been expanding.
Based on careful measurements of how fast distant galaxies are moving away from us and the cosmic background radiation, astronomers estimate that the universe is about 13.7 billion years old

68. The future of the universe
The universe will continue to expand and eventually all of the stars will run out of fuel and burn out. The universe will be cold and dark
The force of gravity will begin to pull the galaxies back together. All of the matter in the universe would be crushed into an enormous black hole
New observations lead many astronomers to conclude that the universe will likely expand forever