Transcript Light
Sally Seebode Teacher San Mateo High School CSTA San Jose, October 2012 How do we Experiment? We interact with objects and make observations. How do you interact with a star? All we can do is collect the light stars send us. We learn about stars by collecting and interpreting the light they send us. Artists concept of Giant Magellan Telescope Understanding information from light • What is light? • What creates light? • What information can we get from light? What is light? • Light is a common term used to refer to Electromagnetic Radiation • Types of electro magnetic radiation: Visible light, radio wave, X-rays, infra red waves (heat), ultra violet waves, gamma rays, microwaves Teaching Light Spectrum White light is composed of many different wavelengths Demonstration: make a rainbow Equipment: Overhead projector, 2 sheets of paper to make a slit, a diffraction grating (Edmund Scientific 2 12” x 6” sheets $8.95 or 15 gratings $7.95) With sheets of paper, make a thin slit on overhead. Place diffraction grating over projector lens. Show students that white light splits into rainbow of colors. Discuss colors and order/energy if appropriate. Students record colors as they see them and label them appropriately. Making the Invisible, Visible Introducing Infra-red The Herschel Experiment: Many online sources. http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/h erschel_experiment.html Making the Invisible, Visible Introducing Infra-red The Herschel Experiment: Students find that the thermometer just outside the light gets the hottest. Use this to instruct that there is light that our eyes cannot detect. Be careful not to interpret that it is the most energetic light. Making the Invisible, Visible Introducing Infra-red Get the fire department to bring their thermal camera to class for the day. Or Have students look through following website IR images Understanding information from light •• What is light? •• What creates light? •• What information can we get from light? How light is created? • Light originates from a vibration of a charged particle (typically an electron) • This vibration causes a pattern of electric and magnetic fields that spread away from the source in all directions. Electron What type of things emit light? To emit light, an object must have thermal energy: moving particles. What types of things have these? Anything with temperature All matter emits light All bodies in the Universe have some temperature. • All bodies are composed of molecules/atoms • When molecules “jiggle” = thermal motion • Temperature is a measure of thermal motion • Temperature of the Universe > 0 Kelvin So,…. All matter emits light: black body radiation Type of Light links to Temperature • Background Cosmic Radiation – radio waves, no visible light • People (300 K) – Infrared, no visible light • Hot Stove (700 K) – Red, orange • Hot Iron (1000 K) – Red, yellow, blue-white • Star (3000 – 15000 K) – “cool” = reddish white Betelgeuse – “hot” = bluish white Sirius Understanding information from light •• What is light? •• What creates light? •• What information can we get from light? Interpreting Light • Objects do not emit just one wavelength of light. They emit ranges. Their peak λ corresponds to their temperature Spectral Energy Distributions A spectral energy distribution (SED) is a plot of brightness (flux) versus wavelength of light from a given star or stellar system. Objects at different temperatures have distinguishable SEDs. Example: Star Spectral Types: O,B,A,F,G,K,M SED Tool SED Tool Students identify a main sequence star’s: • spectral type • temperature • radius • Distance from us SED 1 Focuses on spectral type and temperature SED Tool Students determine distance and spectral type of a star. SED II You can use given data or get archival data from SIMBAD, or make photometric measurements from a telescope. Planetary Nebula White Dwarf Active Galactic Nuclei A team of students worked identifying stellar objects from photometric data from the Kepler survey (KIC). Planetary nebula, white dwarfs, X-ray binaries, cataclysmic variables, Using SEDs, able to identify with about 80% accuracy Further ways to interpret light Noticing light that is missing also informs us about objects and helps us describe them. Analogy: cloud passes over head, you may not have to see it to know it is there. Teaching Spectroscopy When light passes through a medium, some light is removed Demonstration: spectroscopy with filters Equipment: Overhead projector, 2 sheets of paper to make a slit, diffraction grating, Arbor Scientific Color Filter Set (6 pack) ($12) Place filters over half of slit on overhead so diffraction grating is splitting white light and filtered light. Students record colors from filtered light as they see them. They make statements next to each spectrum stating filter used and color(s) missing (absorbed). Teaching Spectroscopy Knowing what light is removed, tells us about the substance the light passed through. Spectrum of Sun Describe what you see? What did the sunlight pass through to create these black lines (absorption lines)? Photo from the Canadian Space Agency Teaching Spectroscopy Connect rainbow type spectra to 2 D graphical representation. Indicates Calcium H delta Indicates 4101 Å Hydrogen H gamma 4340 Å Epsilon Aurigae April 19, 2009 Spectroscopy Resources CSM Catalog website:http://collegeofsanmateo.edu/astronomy/i mages/SpectraCatalog.pdf ARBSE NOAO Astronomy Research Based Science Education website Kepler Transit Resources website Thank You Please email me if you would like a copy of this presentation or particular links/websites or if you have questions about what was presented here. [email protected]