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

This weekend: more reading, HW question to turn in, quiz for next Thurs.

Clicker Question—Light Hopefully you know that light carries energy . But does light carry momentum? Yes, always Sometimes No! Light does NOT have mass!

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

Hopefully you know that light carries energy . But does light carry momentum?

Yes, always

Sometimes

No! Light does NOT have mass!

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

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???)

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

Shadow demo; Eclipses

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!

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!

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

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!

What color is this shadow?

Green

Black

Gray

White

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)

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

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

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

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???)

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

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

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 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 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)

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

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

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

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

Image of sun at particular frequency absorbed / emitted by hydrogen.

Dark lines are “clouds” of hydrogen in the atmosphere of the sun (absorption)

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!

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?

“ Sunspots” are cooler spots on the sun…as low as 4000K apparent temperature compared with 5700K normal.

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

Apparently at a minimum for sunspots right now.