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

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

Flame and Spectra for Strontium Emission Spectrum for Strontium

Flame and Spectra for Barium Emission Spectrum for Barium

Flame and Spectra for Calcium Emission Spectrum for Calcium

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

Flame and Spectra for Lithium Emission Spectrum for Lithium

Flame and Spectra for Potassium Emission Spectrum for Potassium

Flame and Spectra for Copper Emission Spectrum for Copper

Comparing Unknown Flame to Known Flame Colors Sr Ba Ca Na Unknown Flame is ??? Li K Cu

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

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”).

Bright Line (Emission) Spectrum for Hydrogen Ha 410.2 nm 486.1 nm 398.1 nm 434.1 nm 656.3 nm

Bright Line Spectra for Mercury

Bright Line (Emission) Spectra Helium Mercury Neon Sodium Na

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

Emission Spectra of the Elements

Emission Spectra of the Elements

Emission Spectra of the Elements

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

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

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

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

Pt 3 - Incandescent objects and Black Body Radiation

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

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

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

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.

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.

Incandescent Metals Temperature Color

Incandescent Metal Temperatures and Colors Infra-Red 500 - 550 °C Red Hot 750 – 850 °C Orange Hot 950 – 1050 °C Yellow Hot 1050 – 1150 °C White Hot >1450°C

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, http://www.windows.ucar.edu

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, http://www.windows.ucar.edu

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, http://www.windows.ucar.edu

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, http://www.windows.ucar.edu

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, http://www.windows.ucar.edu

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, http://www.windows.ucar.edu

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.

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.

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.

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

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

Harvard Spectral classification of stars Class O - Blue (super hot - 41,000o K) (Range = 28,000 - 50,000o K) Class B - Blue/White (Range = 10,000 - 28,000o K) Class A - White (Range = 7,500 - 10,000o K) Class F - Yellow-White (Range = 6,000 - 7,500o K)

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).

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.

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.

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.

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

Pt 5 dark line spectra of stars

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

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.

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

Absorption Spectrum of the Sun Emission Spectrum of Sodium

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

Absorption Line of Sodium by a Distant Planet’s Atmosphere

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

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

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

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

The End!!

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.