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09 Feb 19 Blackbody, Sun
 

09 Feb 19 Blackbody, Sun

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More about visible light; blackbody radiation; facts about the sun; looking at an image of the sun (unfortunately no sunspots); eclipses

More about visible light; blackbody radiation; facts about the sun; looking at an image of the sun (unfortunately no sunspots); eclipses

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    09 Feb 19 Blackbody, Sun 09 Feb 19 Blackbody, Sun Presentation Transcript

    • Today: Shadows, Eclipses, Blackbody Radiation, The Sun (also eliminating some crayon bias)
      • This weekend: more reading, HW question to turn in, quiz for next Thurs.
      Hydrogen clouds on the Sun
    • Clicker Question—Light
      • Hopefully you know that light carries energy . But does light carry momentum?
      • Yes, always
      • Sometimes
      • No! Light does NOT have mass!
    • Clicker Question—Light
      • Hopefully you know that light carries energy . But does light carry momentum?
      • Yes, always
      • Sometimes
      • No! Light does NOT have mass!
      Optical tweezers! Solar sails! http://en.wikipedia.org/wiki/Solar_sail; JPL
    • Light is an electromagnetic wave, so all of this still holds true
        • Carries energy
        • Has momentum (oomph) (but does NOT have mass)
        • In a vacuum travels at “light speed” (duh?)
        • Behaves like particle AND wave (what the???)
      Many light phenomena can be understood by treating visible light as if it were particles Shadows and Eclipses Lunar Eclipse, Wikipedia http://www.flickr.com/photos/zen/2516147072/ Study the crispness of shadows you see outside to see effects of umbra and penumbra
    • Shadows and Eclipses Lunar Eclipse, Wikipedia View from perspective of observer on earth, looking up at moon
    • Shadows and Eclipses
      • Shadow demo; Eclipses
      http://aa.usno.navy.mil/data/docs/LunarEclipse.html Wikipedia David Ball
    • Clicker Question – Lunar Eclipse
      • What phase is the moon in a few minutes before and a few minutes after a total lunar eclipse?
      • Full moon
      • Exactly half moon
      • New moon
      • Any phase, depending on when the eclipse happens!
    • Clicker Question – Lunar Eclipse
      • What phase is the moon in a few minutes before and a few minutes after a total lunar eclipse?
      • Full moon
      • Exactly half moon
      • New moon
      • Any phase, depending on when the eclipse happens!
    • Solar Eclipses Solar Eclipse viewed from the space station Next total solar eclipse in US: August 27, 2017 http://xjubier.free.fr/en/site_pages/solar_eclipses/TSE_2017_GoogleMapFull.html
    • Clicker Question – Shadow colors
      • What color is this shadow?
      • Green
      • Black
      • Gray
      • White
    • Clicker Question – Shadow colors
      • What color is this shadow?
      • Green
      • Black
      • Gray
      • White
      I say it’s green!
    • From atomic emission lines to incandescence (blackbody radiation) http://www.physics.umd.edu High pressure mercury Solar spectrum Low pressure mercury
    • EVERY object emits radiation, even you and me!
      • Solid objects usually emit blackbody radiation
      • peak frequency  Temperature
      • but a continuous, broad spectrum
      • Physics can predict exactly the spectrum
      • Planck’s Law of blackbody radiation
      Remember this: Peak frequency of light proportional to Temperature f peak  T (Wein’s displacement law) (Don’t remember this)
    • Infrared cameras—we can’t miss this fun http://www.youtube.com/watch?v=1th1MYyosQk&feature=related Scientists identified this creature based on it’s infrared spectrum http://www.youtube.com/watch?v=xQVPTlSaoys I don’t know what this is, but it’s awesome
    • Clicker Question—Blackbody spectrum
      • You are looking at several different very hot objects of differing temperatures. Which one is hotter, one that glows red, yellow or white?
      • Glowing red
      • Glowing yellow
      • Glowing white
    • Clicker Question—Blackbody spectrum
      • You are looking at several different very hot objects of differing temperatures. Which one is hotter, one that glows red, yellow or white?
      • Glowing red
      • Glowing yellow
      • Glowing white
    • The blackbody spectrum can reveal the temperature of a glowing object Spectrum viewer: http://www.mhhe.com/physsci/astronomy/applets/Blackbody/applet_files/BlackBody.html Color Temperature: http://www.techmind.org/colour/coltemp.html
    • Blackbody radiation demos
      • Viewing infrared radiation
      • Even infrared or “heat waves” can behave like rays of light
          • (momentum???)
    • Some facts about the Sun (no need to memorize exact numbers!)
      • The Sun is 150 million km away (90 million miles)
      • (8 light minutes)
      • About 109 times the diameter of Earth
      • 300,000 times the mass of the Earth
      • 73% Hydrogen, 25% Helium
      Let’s watch the first minute of this video: http://www.youtube.com/watch?v=gdLaPhNBOcU
    • Clicker Question—Sun spectrum
      • The core of the Sun is approximately 15,000,000 Kelvin (fueled by thermonuclear fusion of Hydrogen into Helium). However, the spectrum we view is as if we are looking at a 5700 K blackbody. Why?
      • The Sun is a terrible approximation of a blackbody
      • The Sun is opaque so we can’t “see” the interior. We see the outer part which is actually cooler.
      • The Earth’s atmosphere modifies the Sun’s spectrum severely, so we don’t see it as 15,000,000 K
      • The spectrum is drastically red-shifted because of the distance to Earth.
    • Clicker Question—Sun spectrum
      • The core of the Sun is approximately 15,000,000 Kelvin (fueled by thermonuclear fusion of Hydrogen into Helium). However, the spectrum we view is as if we are looking at a 5700 K blackbody. Why?
      • The Sun is a terrible approximation of a blackbody
      • The Sun is opaque so we can’t “see” the interior. We see the outer part which is actually cooler.
      • The Earth’s atmosphere modifies the Sun’s spectrum severely, so we don’t see it as 15,000,000 K
      • The spectrum is drastically red-shifted because of the distance to Earth.
    • The Sun has layers and atomosphere just like Earth
      • Just like in the Earth’s atmosphere, the gasses of the sun are cooler farther away from the center (mostly)
    • The solar spectrum Solar spectrum demo – see continuous spectrum & also absorption spectra (hydrogen)
    • Clicker Question – What color is the sun?
      • If you take a picture of the noon-time sun (very very short exposure!), what color would it be?
      • White
      • Yellow
      • Blue
      • Green
      • Red
    • Clicker Question – What color is the sun?
      • If you take a picture of the noon-time sun (very very short exposure!), what color would it be?
      • White
      • Yellow
      • Blue
      • Green
      • Red
    • Clicker Question – What color is the moon?
      • If you take a picture of the high moon, what color would it be?
      • White
      • Yellow
      • Blue
      • Green
      • Red
    • Looking at the various “colors” emitted by the sun produces fascinating images.
      • Image of sun at particular frequency absorbed / emitted by hydrogen.
      • Dark lines are “clouds” of hydrogen in the atmosphere of the sun (absorption)
      Many faces of the sun http://www.spaceweathercenter.org/SWOP/Interactives/1.html
    • The Sun’s atmosphere is visible during total eclipse
      • Currently there is a huge mystery about the Sun’s atmosphere…it is MUCH hotter than the “photosphere” that we “see!” It’s still a mystery why!
      • “ Sunspots” are cooler spots on the sun…as low as 4000K apparent temperature compared with 5700K normal.
      Image of sun this morning Solar image demo – The disc on the wall is actual image of the sun! What color is it? Can we see spots?
    • In addition to eclipses, we are unlucky with sunpots too!
      • Apparently at a minimum for sunspots right now.
      Current image of the sun: http://nsosp.nso.edu/VIDEOIMG/isoon/latest_w.jpg