Chapter 5 Key Summary1. Almost all knowledge of the universe beyond Earth comes from light. Light can tell us about objects in space: temperature, composition, speeds, and more.2 Light is an electromagnetic wave,Wavelength (λ) : length between crests.Amplitude: height, high amplitude means brighter light.Frequency (f): number of waves that pass by each second.Period (P): time to complete one cycle.3. speed of light c= λf (wavelength x frequency) , speed light is constant=3x108 m/s in vacuum, this means that higher frequency light has smaller wavelength.Four diagrams that show that a wave is characterized by the distance from one peak to the next wavelength, the frequency of the peaks, the maximum deviations from the medium's undisturbed state (amplitude), and the speed at which the wave patterns travels from one place to another. Diagram (a) has a wavelength with two peaks. The length of the wavelength is measured from the first peak to the second peak. The amplitude distance is measured from the peak down to the zero line. Diagram (b) shows a wave and a dotted wave that are traveling towards the right. The waves travel at a velocity of v. Diagram (c) shows a wave with a longer wavelength and a lower frequency. The wave has two peaks and the length from one peak to the other peak is denoted by the symbol lambda. Diagram (d) shows a wave with a shorter wavelength and a higher frequency. The wave has five peaks and the length from one peak to another peak is denoted by the symbol lambda.Wavelength and Frequency Relationship. Credit: 21st Century Astronomy, W.W. Norton.4. Our eye recognize f (frequency) as color. Light with all color is white light. Visible spectrum is a small range of wavelengths that humans can see. Red light has longest wavelength, smallest f; Violet light has shortest wavelength, largest f. "Roy G. Biv." can be used to remember the spectrum of visible light from red to violet. The whole electromagnetic spectrum consists of (from high f): gamma ray, x ray, ultraviolet, visible, infrared, microwave, radio wave. An electromagnetic spectrum that shows the relationships between frequency, wavelength, and the types of electromagnetic radiation. It ranges from gamma rays to radio waves. The x axis on top is labeled with frequency (Hertz) that ranges from 3 times 10 to the power of 20 to 3 times 10 to the power of 6. The x axis on the bottom is labeled with wavelength measurements that range from nanometers, micrometers, millimeters, centimeters, meters, and kilometers. Gamma rays are shown from between 3 times 10 to the power of 20 to about 3 times 10 to the power of 18 Hertz and the wavelength measures from 0.001 nanometers to about 0.1 nanometer. X-rays are shown from 3 times 10 to the power of 18 to about 3 times 10 to the power of 15.5 Hertz and the wavelength measures from 0.1 nanometers to about 50 nanometers. Ultraviolet is shown from about 3 times 10 to the power of 15.5 to about 3 times 10 to the power of 14.5 Hertz and the wavelength measures from about 50 nanometers to about 200 nanometers. Infrared is shown from 3 times 10 to the power of 14 to about 3 times 10 to the power of 11 Hertz and the wavelength measures from 1 micrometer to about 800 micrometers. Microwave is shown from about 3 times 10 to the power of 11 to about 3 times 10 to the power of 9.5 Hertz and the wavelength measures from 1 millimeter to about 5 centimeters. Radio is shown from about 3 times 10 to the power of 9.5 to 3 times 10 to the power of 5 Hertz and the wavelength measures from 5 centimeters to 1 kilometer. FM radio is between 3 times 10 to the power of 8 and 3 times 10 to the power of 7 and the wavelength measures between 2 meters to 5 meters. AM radio is between 3 times 10 to the power of 6 and 3 times 10 to the power of 5 and the wavelength measures between 100 meters and 600 meters. Television is shown between 3 times 10 to the power of 9 and 3 times 10 to the power of 7 and the wavelength measures from between 50 centimeters to 5 meters. Below the spectrum is a zoomed in view of the visible light spectrum. The x axis is labeled with wavelength (nanometers) that range from 350 to 750. Violet ranges from 380 to 450 nanometers. Blue ranges from 450 to 495 nanometers. Green ranges from 495 to 570 nanometers. Yellow ranges from 570 to 590 nanometers. Orange ranges from 590 to 620 nanometers. Red ranges from 620 to 750 nanometers.Electromagnetic SpectrumElectromagnetic Spectrum. Credit: 21st Century Astronomy, W.W. Norton.5. Light behave as particles when interacting with matter: photons – packets of energy. Energy carried by photon depends on its frequency (color), E = hf ["h" is called Planck's Constant]. Bluer light (here this bluer means higher f) carries more energy per photon. That is why x-ray with high f can penetrate our body and UV (ultra-violet) light can penetrate our skin and are harmful. Study Tool: AstroTour6. Atomic Energy levels: Electrons can only have certain energies; The energy is quantized (not continuous). Each type of atom has a unique set of energies. Lowest energy is the ground state. Study Tool : AstroTour7. Emission Spectrum: when an electron drops to a lower energy state, it emits a photon and the photon's energy is equal to the energy difference between the two levels. Absorption: Spectrum: when an electron absorbs the energy of a photon, moving the electron to a higher energy level. The photon's energy equals to the energy difference between the two levels. Study Tour: AstroTour A diagram that shows a photon with energy emitting when an atom in a higher energy state decays to a lower energy state. The downward arrow indicates that the atom went from a higher state with energy E subscript 2 to a lower state with energy E subscript 1. The decay caused by this emits a photon as depicted by the squiggly arrow. Next to the energy states is an energy diagram that increases in energy the more is goes up. E subscript 1 is shown on the lower half of the arrow and E subscript 2 is shown on the top half of the arrow. An arrow traveling from E subscript 2 to E subscript 1 shows that E subscript photon equals E subscript 2 minus E subscript 1 and that lambda subscript 2 becomes subscript 1. A text box that points to the squiggly arrow reads, Emission and AbsorptionEmission and Absorption. Credit: 21st Century Astronomy, W.W. Norton.9. Each element has its own distinctive set of electron energy levels, emits (or absorbs) its own pattern of colors, called emission (absorption) line spectrum, like fingerprints. By identify the unique pattern, the spectrum reveals a star's composition, temperature, and more.An emission spectra for helium, Argon, neon, and sodium. The x axis is labeled with wavelength, lambda (nanometers) that ranges from 350 to 650. Each type of atom has a unique spectral fingerprint. Sodium has yellow wavelengths.Emission Spectrum for Helium, Argon, Neon and SodiumCredit: 21st Century Astronomy, W.W. Norton.10. A hot, dense glowing object (blackbody) emits a continuous spectrum. Hotter objects emit more light at all frequencies and hotter objects emit photons with a higher average energy (or higher f). As a result, a bluer object is hotter than a redder one. Our Sun peak at Yellow-Green wavelength, a hotter star could peak at blue light and make it blue in color. Study Tool: AstronomyInAction A graph that shows blackbody spectra emitted by sources with temperatures of 2,000 Kelvin, 3,000 Kelvin, 4,000 Kelvin, 5,000 Kelvin, and 6,000 Kelvin. The x axis is labeled with wavelength, lambda (nanometers) that ranges from 0 to 3,000 nanometers. The y axis is labeled with intensity. On the graph, the visible light spectrum is shown ranging from 380 to 750 nanometers. There are five wavelengths present on the graph. The wavelength's equations at 6,000 Kelvin are: Upper T equals 6,000 Kelvin and lambda subscript peak equals 480 nanometers. The wavelength's equations at 5,000 Kelvin are: Upper T equals 5,000 K and lambda subscript peak equals 580 nanometers. The wavelength's equations at 4,000 Kelvin are: Upper T equals 4,000 K and lambda subscript peak equals 730 nanometers. The wavelength's equations at 3,000 Kelvin are: Upper T equals 3,000 K and lambda subscript peak equals 970 nanometers. The wavelength's equations at 2,000 Kelvin are: Upper T equals 2,000 Kelvin and lambda subscript peak equals 1,450 nanometers. Making an object hotter makes it more luminous and shifts the peak of its Planck spectrum to shorter wavelengths.Blackbody spectrum with different temperatureBlackbody spectrum, the higher the temperature, the more the radiation and the higher the photon's energy. Credit: 21st Century Astronomy, W.W. Norton. 11. Doppler's effect: The motion of a light source toward or away from an observer changes his/her perception of the wavelength of the waves reaching us. When moving towards, the wavelength is squeezed shorter or higher frequency, "blue shifted" When moving away, the wavelength is stretched longer or lower frequency, "red shifted". The same is true if the observer moves or both of the source and observer moved away or towards each other. When source and observer motion is perpendicular, then no Doppler's effect (see picture below).Title: Doppler Effect - Description: A diagram showing the motion of a light or sound source relative to an observer. The moving source of light is in the center and is traveling to the right. There are three observers, one to the left of the source light, one to the right of the source light, and one below the source light. The waves that reach the observer to the left are spread out to longer 11. Doppler shift applies to any waves. If it is sound wave, then the shift can be heard as pitch change. If it is visible light wave, then the shift can be seen as color change. When The more the speed that an observer and source moving towards or away from each other, the more the shift. Study Tool: AstroTour