Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7The Sun is One of Many StarsSlide 9Slide 10Slide 11Parsec = distance where a star shifts by 1” over a 1/2 yearAngular SizesSlide 14Slide 15Slide 16In this class we’ll often mush both views together.1. WavelengthSlide 19Slide 20Slide 21Slide 22Slide 23Slide 242. Frequency3. VelocitySlide 27But, distances between objects in space get really big, really fast…Slide 29Slide 304. EnergySlide 32Slide 33Which has a longer wavelength?Slide 35Slide 36Slide 37Slide 38PowerPoint PresentationSlide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46The Magnitude ScaleSlide 48Slide 49Astronomy 101Astronomical Observations:Distance & Light7/2/09Astronomy 101Astronomy Picture of the DayAstronomy 101Something Cool:Lasers on the MoonAstronomy 101Outline for TodayAstronomy Picture of the DaySomething Cool BusinessReturn Lab 2 Q&A session Distance LectureLight LectureMinute WritingBreakLab 4Astronomy 101Questions for TodayHow big is the Solar System, Galaxy, Universe?How can we use parallax to find distance?What is light?What is the electromagnetic spectrum and how does wavelength relate to energy?What are brightness and luminosity and how do they change with distance?How can we use standard rods and candles to find distance?Astronomy 101Solar SystemAstronomy 101Solar SystemThe Sun is One of Many StarsSolar SystemMilky WayThe Local Group of GalaxiesAstronomy 101htt://xkcd.com/482htt://xkcd.com/482Astronomy 101Place in Order from Smallest to Largest:Galaxy, Solar System, Universe, Local Galaxy ClusterA) Solar System, Galaxy, Local Cluster, UniverseB) Local Cluster, Galaxy, Solar System, UniverseC) Galaxy, Solar System, Universe, Local ClusterD) Solar System, Universe, Galaxy, Local ClusterAstronomy 101Place in Order from Smallest to Largest:Galaxy, Solar System, Universe, Local Galaxy ClusterA) Solar System, Galaxy, Local Cluster, UniverseB) Local Cluster, Galaxy, Solar System, UniverseC) Galaxy, Solar System, Universe, Local ClusterD) Solar System, Universe, Galaxy, Local ClusterParallaxAngular SizesWe measure how big objects appear to be in degrees, arcminutes, & arcseconds.1 degree = 60 arcminutes = 3600 arcsecondsAngular Sizes1 degree = 60 arcminutes = 3600 arcsecondsParallax -> Distance Parallax Angle ⇩, Distance ⇧distance ∝ 1/(parallax angle)The Facts of LightEmission of Light = RadiationLight sometimes acts like a massless particleLight also acts like a wave.Light as Wave & Particle• We’ll talk about emission and absorption of individual photons.• We’ll also often assign wave-like qualities to it1.Wavelength2.Frequency3.Velocity4.EnergyWavelengthThe distance over which the wave pattern repeats is the wavelength.WavelengthThe color of light depends upon its wavelength. Short wavelengths areBlue Long wavelengths areRed(radio)Wavelength We see with our eyes only a tiny fraction of the range of possible wavelengths“Logarithmic scale”: each tic mark represents a factor of ten increase. Size of atomic nucleus!Size of Mt. Everest!1. Wavelength(radio)If you were to design a pair ofglasses for seeing animals atnight, you would want them toconvertA) Infrared photons to X-ray photonsB) X-ray photons to optical photonsC) Infrared photons to optical photonsD) Optical photons to UV photonsIf you were to design a pair ofglasses for seeing animals atnight, you would want them toconvertA) Infrared photons to X-ray photonsB) X-ray photons to optical photonsC) Infrared photons to optical photonsD) Optical photons to UV photonsFrequencyThe rate at which peaks pass a given location is the frequency.VelocityThe speed of light is constant.The speed of light is closely related to its wavelength and its frequency.If you know one, you can calculate the other! Speed of light (c) = distance between peaks = wavelength X frequencytime between peaksLight YearsHow far light travels in a year–About 1016 meters–About 5.8 ∗1012 milesThe Sun is eight light minutes awayWhy use light years?Nearest Star: 40,000,000,000,000 kilometers (4 X 1013 km) = 4 light years206,000 times further than the Earth is from the Sun) (or 1.3 parsecs)It takes a green laser 2.5 secondsto reach the surface of the Moon,bounce off and return.How long does it take a radio wave to complete the same journey?A) Less time because radio waves have smaller frequencyB) More time because radio waves have longerwavelengthsC) More time because radio waves are less powerfulD) The same timeIt takes a green laser 2.5 secondsto reach the surface of the Moon,bounce off and return.How long does it take a radio wave to complete the same journey?A) Less time because radio waves have smaller frequencyB) More time because radio waves have longerwavelengthsC) More time because radio waves are less powerfulD) The same timeEnergyThe energy of a photon depends entirely on its frequency (or wavelength)FREQUENCYWAVELENGTHEnergy isgreater when…..EnergyDangerous!!!Burns you! Goes through you!Mostly Harmless.(Microwaves only hurt because they have a peculiar interaction with water)EnergyWatch your intuition here!BLUE• Short wavelength• High frequency • HIGH ENERGYRED• Long wavelength• Low frequency • LOW ENERGYWhich has a longer wavelength?A) Ultraviolet light (UV) B) Visible light C) Infrared Light (IR)Which has a longer wavelength?A) Ultraviolet light (UV) B) Visible light C) Infrared Light (IR)How does light interact with matter?EmitReflectAbsorbTransmitWhich is an example of reflected light?A) UV Light from the SunB) The green color of grassC) Heat from a stoveD) Gamma ray radiation from UraniumWhich is an example of reflected light?A) UV Light from the SunB) The green color of grassC) Heat from a stoveD) Gamma ray radiation from UraniumThe brightness of a star depends on both distance and luminosityBrightnessLuminosity: Amount of power a star radiates (energy per second = Watts) Apparent Brightness or Flux: Amount of starlight that reaches Earth (energy per second per square meter)Luminosity And Apparent BrightnessThese two stars have about the same luminosity -- which one appears brighter?A. Alpha CentauriB. The SunThese two stars have about the same luminosity -- which one appears brighter?A. Alpha CentauriB. The SunAnother Inverse Distance Squared Law Flux = LuminosityDistance2How would the apparent brightness of Alpha Centauri change if it were three times farther away?A. It would be only 1/3 as brightB. It would be only 1/6
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