Stars, Galaxies & The Electromagnetic Spectrum

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)

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 tuljooz), 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