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Astronomy 1020 Stellar Astronomy Spring_2016 Day-15 Course Announcements • 1st “Hot Topics in Science”: Coming Soon • • Topics this semester are: Human Cloning, Environmental Toxicology, & Fracking … includes pizza. • Dark Night Observing: Mon. 2/29 & Wed. 3/2 – 7:30pm at the APSU Observatory Exam-2 – Fri. 3/4 Chapters 5 & 6 Smartworks Chapters 5 & 6: Due Fri. 3/4 Spring Break Mar. 5-13 (Sat.-Sun.) • APSU Research and Creativity Forum April 15, 2016 • • • • • Abstracts are due: 4:00pm Fri., March 18 Feb. 29 – Last day to drop with an automatic “W” Apr. 1 – Last day to drop a class with W, F, FA The wavelengths at which atoms emit and absorb radiation form unique spectral fingerprints for each atom. They help determine a star’s composition, temperature, and more. The motion of a light source toward or away from us changes our perception of the wavelength of the waves reaching us. Doppler effect. MATH TOOLS 5.2 If you know the wavelength of light you are observing as well as the wavelength of light the object would be emitting if it were at rest, you can find the speed of the object using the Doppler effect. Light from approaching objects is blueshifted; the waves crowd together. Light from receding objects is redshifted; the waves are spaced farther apart. The motion of a light source toward or away from us changes our perception of the wavelength of the waves reaching us. Doppler effect. Lecture Tutorial Doppler Shift: (pg. 75) • Work with a partner! • Read the instructions and questions carefully. • Discuss the concepts and your answers with one another. Take time to understand it now!!!! • Come to a consensus answer you both agree on. • If you get stuck or are not sure of your answer, ask another group. Concept Quiz—Doppler Shift Hydrogen emits light at = 656 nm. You see a distant galaxy in which the light from hydrogen has = 696 nm. This galaxy is A. moving toward us. B. moving away from us. Temperature is a measure of the average speed of the motions of atoms. Kelvin scale: Water freezes/boils at 273 K / 373 K. Absolute zero is when thermal motion stops. Emitted Light Luminosity: amount of light leaving a source. The amount and type of light leaving a source changes as an object heats up or cools down. The hotter an object is, the more luminous it is. The hotter an object is, the bluer it is. Dense objects emit a blackbody (or Planck) spectrum. Continuous. Gives light at all wavelengths. Example: incandescent light bulb. For two objects of the same size, the hotter one will: • Emit more total light at all wavelengths. • Emit more total energy every second. • Emit light at shorter wavelengths, on average. Stefan’s Law Flux is the total amount of energy emitted per square meter every second (the luminosity per area). Then: F T 4 where T is the temperature, F is the flux, and (sigma) is called the StefanBoltzmann constant. Hotter objects emit much more energy (per square meter per second) than cool objects. Wien’s Law The peak wavelength of a blackbody is inversely proportional to its temperature. 2 , 900 , 000 nm K peak T Peak wavelength peak : the wavelength of light of a blackbody that is emitted the most. Here the wavelength is in nanometers and the temperature is in kelvin. “Hotter means bluer.” MATH TOOLS 5.3 With the Stefan-Boltzmann law, you can find Earth’s flux using its average temperature of 288 K. Using Wien’s law, you can find the Sun’s surface temperature using the fact that its peak wavelength is around 500 nm. Luminosity is the total energy (light) emitted by an object in each second. Stefan-Boltzmann law Luminosity depends on an surface area (A), 4 and its temperature (T ); Surface Area ∝ R Luminosity = 4π R T 2 2 4 Big and Hot objects have greater luminosity than small cool objects Great Blizzard of 2015 – Part 3 Exam Sadistics Metric Number Mean StdDev Median Mode High Low Ex-1 28/32 70.7 15.3 73.2 --95.2 40 How BIG Are the Stars? While We Wait for Everyone Solar Flare Luminosity is the total energy (light) emitted by an object in each second. Stefan-Boltzmann law Luminosity depends on an surface area (A), 4 and its temperature (T ); Surface Area ∝ R Luminosity = 4π R T 2 2 4 Big and Hot objects have greater luminosity than small cool objects Lecture Tutorial Luminosity: (pg 55) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. Hertzsprung-Russell Diagram Luminosity (solar units) 10,000 1 4 1,000 100 10 3 1 0.1 0.01 2 5 0.001 0.0001 20,000 10,000 Temperature (K) 5,000 Which star is Hot and Dim? Luminosity (solar units) 10,000 1 4 1,000 100 10 3 1 0.1 0.01 2 5 0.001 Temperature (K) 0.0001 20,000 10,000 Temperature (K) 5,000 Which star is Cool and Dim? Luminosity (solar units) 10,000 1 4 1,000 100 10 3 1 0.1 0.01 5 0.001 2 Temperature (K) 0.0001 20,000 10,000 Temperature (K) 5,000 Which star is Largest? Luminosity (solar units) 10,000 1 4 1,000 100 10 3 1 0.1 0.01 2 5 0.001 0.0001 20,000 10,000 Temperature (K) 5,000 Which star is smallest? Luminosity (solar units) 10,000 1 4 1,000 100 10 3 1 0.1 0.01 5 0.001 Temperature (K) 0.0001 20,000 10,000 Temperature (K) 5,000 2 L B 2 4r Brightness is the amount of light arriving at a particular place. Decreases as the distance from a light source increases, obeying an inverse square law. The light spreads out over a greater area. Lecture - Tutorial: Blackbody Radiation (pg. 59) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. Star A Star A Star A Star D Energy Star C Output per second Star B VIBGYOR VIBGYOR Wavelength VIBGYOR Which has the longer peak wavelength? 1. Star A 2. Star C Star A Energy Output per 3. Same Star C second VIBGYOR Wavelength Which has the lower surface temperature? 1. Star A 2. Star C Star A Energy Output per 3. Same Star C second VIBGYOR Wavelength Which star looks red? 1. Star A Star A Energy 2. Star C 3. Both 4. Neither Output per Star C second VIBGYOR Wavelength Which has the greater energy output? 1. Star A Star A Energy 2. 3. Star C Same Output per Star C second VIBGYOR Wavelength Which star is larger? 1. Star A 2. Star C Star A Energy Output per 3. Same Star C second VIBGYOR Wavelength Which star is larger? 1. Star A 2. Star D 3. Same Star A Star D Energy Output per second VIBGYOR Wavelength Try to determine EVERYTHING about how these four stars compare!! Temp, Energy output, color, size (area)….. Object A Energy Output per second VIBGYOR range Object C Wavelength visible range Object B Wavelength visible VIBGYOR Energy Output per second range VIBGYOR Energy Output per second Energy Output per second visible Wavelength visible range Object D VIBGYOR Wavelength The telescope is the astronomer’s most important tool. Purpose: to gather light of all kinds. Two kinds of optical telescopes: reflecting and refracting. Invented in 1608 by Hans Lippershey. Telescopes Telescopes have three functions: 1. Gather light 2. Resolve objects 3. LGP ∝ Area = πR2 Θ = 2.06 X 105 (λ/D) Magnify EXTENDED objects CONNECTIONS 6.1 When light encounters a new material, it can either experience reflection or refraction. In refraction, the light will be bent depending on the value of the index of refraction relative to the first material. CONNECTIONS 6.1 Refraction depends on the wavelength— violet light is bent more than red. Dispersion: the resulting spreading out of the wavelengths of light. Causes chromatic aberration in lenses, which can be fixed by a compound lens. Refracting telescopes use lenses. Objective lens: refracts the light. Aperture: size of the objective lens (larger aperture gathers more light). The objective lens is placed in the aperture. Focal length: distance between lens and the image (longer = larger image). Aperture sets the light-collecting power. Focal length determines the image size. The largest refracting telescope has a 1-meter aperture. Problems with refractors: • Need to be large to have a long focal length. • Lenses suffer from chromatic aberration. Reflecting telescopes use mirrors. There are primary and secondary mirrors. Focal length is determined by the path the light takes reflecting off the mirrors. Reflectors have advantages over refractors. No chromatic aberration. Bigger telescopes due to increased focal length in the same amount of physical space and no need for massive lenses. The largest telescopes in the world are reflectors. A concave mirror focuses light Spherical Aberration Correcting S.A. Spherical aberration can be eliminated by a parabolic shape or a corrector plate Focal Arrangements There are several types of reflecting telescopes Schmidt-Cassegrain MATH TOOLS 6.1 The light-gathering power of a telescope is proportional to the square of the aperture size. A telescope’s magnification depends on the focal lengths of the objective lens or mirror and the eyepiece. Lab This Week • The Spectrometer • What you need to know: You get to visualize the spectra from various sources. Reading ahead in Chapter 5 will help. • •