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?

A. Yes, alwaysB. SometimesC. No! Light does NOT have mass!

Clicker Question—Light

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

A. Yes, alwaysB. SometimesC. 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 energyHas 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 outsideto 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 EclipsesShadow 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?

A. Full moonB. Exactly half moonC. New moonD. 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?

A. Full moonB. Exactly half moonC. New moonD. 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?

A. GreenB. BlackC. GrayD. White

Clicker Question – Shadow colors

What color is this shadow?

A. GreenB. BlackC. GrayD. 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 Temperaturebut a continuous, broad spectrum

Physics can predict exactly the spectrumPlanck’s Law of blackbody radiation

Remember this: Peak frequency of light proportional to Temperature

fpeak 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=relatedScientists identified this creature based on it’s infrared spectrum

http://www.youtube.com/watch?v=xQVPTlSaoysI 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?

A. Glowing redB. Glowing yellowC. 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?

A. Glowing redB. Glowing yellowC. 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

1. Viewing infrared radiation

2. 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% HeliumLet’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?

A. The Sun is a terrible approximation of a blackbody

B. The Sun is opaque so we can’t “see” the interior. We see the outer part which is actually cooler.

C. The Earth’s atmosphere modifies the Sun’s spectrum severely, so we don’t see it as 15,000,000 K

D. 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?

A. The Sun is a terrible approximation of a blackbody

B. The Sun is opaque so we can’t “see” the interior. We see the outer part which is actually cooler.

C. The Earth’s atmosphere modifies the Sun’s spectrum severely, so we don’t see it as 15,000,000 K

D. 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?

A. WhiteB. YellowC. BlueD. GreenE. 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?

A. WhiteB. YellowC. BlueD. GreenE. Red

Clicker Question – What color is the moon?

If you take a picture of the high moon, what color would it be?

A. WhiteB. YellowC. BlueD. GreenE. 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 sunhttp://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