1. Light emissions mini-lab Pt 1: Flame test Wrap up

2. Flame Test
Lithium Sodium Potassium
Electrons in the dissolved metal ions are excited by heat energy from the flame.

3. Flame and Spectra for Strontium
Emission Spectrum for Strontium

4. Flame and Spectra for Barium
Emission Spectrum for Barium

5. Flame and Spectra for Calcium
Emission Spectrum for Calcium

6. Flame and Spectra for Sodium
Vapor
Streetlight
Sodium
Flame
Emission Spectrum for Sodium

7. Flame and Spectra for Lithium
Emission Spectrum for Lithium

8. Flame and Spectra for Potassium
Emission Spectrum for Potassium

9. Flame and Spectra for Copper
Emission Spectrum for Copper

10. Comparing Unknown Flame to Known Flame ColorsSr Ba Ca Na
Unknown
Flame is
??? Li K Cu

11. Light emissions mini-lab Pt 2: review of Bright Line Spectra

12. Bright Line (Emission) Spectra
A bright line spectrum is created by the emission of light when electrons are excited within an atom.
Instead of the gradually changing blend of colors found in a continuous spectrum, there are anywhere from a handful to dozens of discrete (separate) spectral lines.
Each chemical element has a distinctive bright line spectral pattern (sometimes referred to as the spectral “signature”).

13. Bright Line (Emission) Spectrum for HydrogenHa
410.2 nm
486.1 nm
398.1 nm
434.1 nm
656.3 nm

14. Bright Line Spectra for Mercury

15. Bright Line (Emission) Spectra
Helium
Mercury
Neon
Sodium Na

16. Comparing Unknown Spectra to Known SpectraSr Ba
Flame Test – Revisited!!
What is the Unknown?? Ca Na Li K Cu
Emission Spectrum
for Unknown

17. Emission Spectra of the Elements

18. Emission Spectra of the Elements

19. Emission Spectra of the Elements

20. Emission Spectra of the Elements
Each Element has its own distinctive signature or “fingerprint”

21. Fireworks – Phosphorus, Magnesium
Electrons in fireworks are excited by heat energy from the explosive chemical reactions.

22. Neon Signs and Spectrum Tubes
Electrons in gas tubes are excited by high voltage electricity.

23. Emission and Planetary Nebulae
Electrons in nebular gases are excited by high energy ultraviolet radiation from nearby stars.

24. Pt 3 - Incandescent objects and Black Body Radiation

25. Continuous Visible Spectrum
Visible light is just one small part of the vast electromagnetic spectrum.
R O Y G B I V

26. Continuous Visible Spectrum
The visible spectrum is the part of the EM spectrum that our receptors on our retinas and optic nerves can detect!!
R O Y G B I V

27. Continuous Visible Light Spectrum 380 nm – 750 nm
Violet Indigo Blue Green Yellow Orange Red
High Energy
Low Energy

28. Blackbody Radiation
Max Planck noticed that incandescent - hot, glowing solids (such as iron and the tungsten filament in a light bulb) changed colors as they got hotter:
black  red hot  yellow hot  white hot  blue hot
Blackbody radiation is one of the most common forms of E/M radiation since it depends on the heat of a body. All stars obey the process of Blackbody radiation and it is the key to inferring the temperature of stars by observing their color.

29. Blackbody Radiation
(As the object gets hotter, wavelength gets shorter.)
So red hot is not really all that hot!!
The largest incandescent objects in the universe are stars:
black  red hot  yellow hot  white hot  blue hot
Blackbody radiation is one of the most common forms of E/M radiation since it depends on the heat of a body. All stars obey the process of Blackbody radiation and it is the key to inferring the temperature of stars by observing their color.

30. Incandescent Metals
Temperature Color

31. Incandescent Metal Temperatures and Colors
Infra-Red °C
Red Hot 750 – 850 °C
Orange Hot 950 – 1050 °C
Yellow Hot 1050 – 1150 °C
White Hot >1450°C

32. Blackbody Radiation (cont’d)
This graph shows the amount of energy emitted at different wavelengths for three different temperatures.
This is the classic curve of a blackbody radiator. Each of the curves could represent a star at the noted temperatures. For example, a 3000 K star is cooler than our Sun and gives off most of it’s radiation in wavelengths we cannot see (In the Infared!)
Amount of energy vs. wavelength/color
(at different temperatures)
Courtesy of Windows to the Universe,

33. Blackbody Radiation (cont’d)
Notice that, at each of the three temperatures, a blackbody radiates some energy at all wavelengths, so you get a continuous spectrum…
This is the classic curve of a blackbody radiator. Each of the curves could represent a star at the noted temperatures. For example, a 3000 K star is cooler than our Sun and gives off most of it’s radiation in wavelengths we cannot see (In the Infared!)
Amount of energy vs. wavelength/color
(at different temperatures)
Courtesy of Windows to the Universe,

34. Blackbody Radiation (cont’d)
However, a blackbody emits a LOT more energy at certain wavelengths corresponding to the “color” represented by that wavelength:
This is the classic curve of a blackbody radiator. Each of the curves could represent a star at the noted temperatures. For example, a 3000 K star is cooler than our Sun and gives off most of it’s radiation in wavelengths we cannot see (In the Infrared!)
Amount of energy vs. wavelength/color
(at different temperatures)
Courtesy of Windows to the Universe,

35. Blackbody Radiation (cont’d)
At 4000 K, there is more red light being given off (red hot).
This is the classic curve of a blackbody radiator. Each of the curves could represent a star at the noted temperatures. For example, a 3000 K star is cooler than our Sun and gives off most of it’s radiation in wavelengths we cannot see (In the Infared!)
Amount of energy vs. wavelength/color
(at different temperatures)
Courtesy of Windows to the Universe,

36. Blackbody Radiation (cont’d)
At 6000 K, there is more yellow light being given off (yellow hot).
This is the classic curve of a blackbody radiator. Each of the curves could represent a star at the noted temperatures. For example, a 3000 K star is cooler than our Sun and gives off most of it’s radiation in wavelengths we cannot see (In the Infared!)
Amount of energy vs. wavelength/color
(at different temperatures)
Courtesy of Windows to the Universe,

37. Blackbody Radiation (cont’d)
At 8000 K, there is more blue light being given off (blue hot).
This is the classic curve of a blackbody radiator. Each of the curves could represent a star at the noted temperatures. For example, a 3000 K star is cooler than our Sun and gives off most of it’s radiation in wavelengths we cannot see (In the Infared!)
Amount of energy vs. wavelength/color
(at different temperatures)
Courtesy of Windows to the Universe,

38. Blackbody Radiation
Incandescent objects such as stars are called “blackbodies”.
A blackbody:
absorbs ALL radiation – molecules move faster when heated
reradiates ALL that energy back out into the environment
creates a continuous spectrum of light
radiates much more energy as it gets hotter.
blackbody:
Blackbody radiation is one of the most common forms of E/M radiation since it depends on the heat of a body. All stars obey the process of Blackbody radiation and it is the key to inferring the temperature of stars by observing their color.

39. Blackbody Radiation
as it gets hotter, wavelengths ( l ) get shorter & shorter:
Black  Red Hot  Yellow Hot  White Hot  Blue Hot
(Explains why blue giant stars are really hot and red giant stars are relatively cool.)
Black
Blackbody radiation is one of the most common forms of E/M radiation since it depends on the heat of a body. All stars obey the process of Blackbody radiation and it is the key to inferring the temperature of stars by observing their color.

40. Blackbody Radiation
Which star below has the hottest surface temperature?
Sol (The Sun – a yellow dwarf)
Alnitak (Blue Giant)
Betelgeuse (Red Supergiant)
As the object gets hotter, the wavelength gets shorter- So red hot is not really all that hot!!
The largest incandescent objects in the universe are stars.
(Explains why blue giant stars are really hot and red giant stars are relatively cool.)
Blackbody radiation is one of the most common forms of E/M radiation since it depends on the heat of a body. All stars obey the process of Blackbody radiation and it is the key to inferring the temperature of stars by observing their color.

41. Pt 4 ...back to spectral classes of stars !!

42. Spectral classes of stars
Stars “burn” at different temperatures. Each temperature of star has a distinctive spectrum.

43. Harvard Spectral classification of stars
Class O - Blue (super hot - 41,000o K) (Range = 28, ,000o K)
Class B - Blue/White (Range = 10, ,000o K)
Class A - White (Range = 7, ,000o K)
Class F - Yellow-White (Range = 6, ,500o K)

44. The most commonly seen visible spectral lines in stars are: Hydrogen, neutral and ionized Helium, H & K lines of ionized Calcium, the bright yellow pair of neutral Sodium lines, as well as lines for Iron and Magnesium, and a few compounds/molecules (Titanium oxide, CH).

45. Which spectral lines will show up in a class of stars depends more on the element’s sensitivity to the star’s surface temperature than any actual differences in chemical composition.

46. For example, while Hydrogen is present in all stars, H spectral lines are strongest in the white-hot temperatures of a Class A star, followed by Blue-White Class B and Yellow-White Class F stars.

47. In the cooler stars (K and M), the H electron does not receive enough energy to create a bright H spectra, so H lines are weak there.
In hot Class O stars, Hydrogen’s electron gets ripped away, so H lines are weak for Class O.

48. Hertzsprung - Russell Diagram
So, the spectral classes of the stars are based not only on each star’s temperature, but also the variety of elements that are able to create dark line spectra at that temperature.
Main Sequence Stars I II
III IV V VI wd
Spectral Class

49. Pt 5 dark line spectra of stars

50. Corona of the Sun
Cooling gases in the sun’s outer corona absorb certain frequencies of solar radiation.

51. Absorption (Dark Line) Spectrum
An electron in a cooling gas can absorb a photon of a particular wavelength as it jumps to a higher energy level. The photon of light/radio wave “disappears” having been “used” or “absorbed” by the electron. For each wavelength of light absorbed, a black “dark line” appears.

52. Comparison of Emission Spectrum (top) and Absorption Spectrum (bottom) for Hydrogen
410.2 nm
486.1 nm
398.1 nm
434.1 nm
656.3 nm
410.2 nm
486.1 nm
656.3 nm
398.1 nm
434.1 nm

53. Absorption Spectrum of the Sun
Emission Spectrum of Sodium

54. Absorption Spectrum of the Sun
Emission Spectra:
Hydrogen
Helium
Mercury
Uranium

55. Absorption Line of Sodium by a Distant Planet’s Atmosphere

56. Absorption Lines Superimposed on a Star’s Blackbody Curve
Ha Line

57. Absorption Lines Superimposed on a Star’s Blackbody Curve
Spectral Class A Star
Ha Line
Spectral Class K Star

58. A star’s spectrum is a combination of a continuous incandescent black body spectrum with the spectral lines of certain elements removed (dark line spectra)!
Spectral Class A Star
Ha Line
Spectral Class K Star

59. The Spectral Class A star (in blue) shows a distinct absorption line for Hydrogen (the Ha line). The Spectral Class K Star (red line) does not show a distinct Ha absorption line because it is too cool to “activate” its Hydrogen.
Spectral Class A Star
Ha Line
Spectral Class K Star

60. The End!!

61. Hertzsprung - Russell Diagram
Main Sequence Stars I II
III IV V VI wd
Spectral Class
Main sequence stars are “hydrogen-burners”. Going up to the left, stars get brighter and hotter, going from red hot to yellow hot to white hot to blue hot.