January 24, 2000

And then there was light...


 
"The simple have something more than do learned doctors, who often become lost in their search for broad, general laws...The simple grasp the truth of their own, perhaps truer than that of the doctors [of the church] but then they destroy it in unthinking actions."

Umberto Eco, The Name of the Rose, 1980

Assignments:

Read Chapter 4.1, 4.2 of your text, if you haven't already. Also: HW#1
 Also: Look at the reflection of the sun from a window,  the neon signs across from the Bull Run Inn or at the 45th & 15th junction, small white clouds, car headlights, with the "glasses" that you got. 

Name: Ran "Ron" Sivron, Hobbies, 

Something about myself, thanks for Emailing me the information!

Part 1 of today's class: review of some terms from Astronomy 101; Part II: Properties of light.

From the end of Friday's class: Using c=2.9979 x 105 km/s how long does it take to get from: 
Q1: How long for light to arrive from the sun to earth, a mere 150 million km? (500 seconds, 8 minutes 20 seconds)
Q2: to one of the nearest star; Sirius, the brightest star in the night sky, a mere 72 trillion km from earth? (2.4 x 108 seconds, 8 years); 

M32 in Andromeda, the only galaxy visible with the naked eye (2 million years); 

The edge of the observable universe (12-15 billion years).

So, What can we tell about those stars by just looking at them with the naked eye?\

Not Much:

Starting next week, observations. (Redshift2 presentation)

You can tell that they rise in the east, set in the west. 
Evidence that the earth is spinning on its axis.

You can tell that the same groups of stars rise at sunset every day of the year, but that zodiac constellation gemini crosses rises in december evenings, Cancer in January, Leo in February, Virgo in March etc. 
That's just because the earth is orbiting the sun.(explain on board).

So what CAN we tell about the stars from observing them?

Their Brightness! 

Their Color!

Both related to the light's behavior as a wave.

Look at the stars this week, if you can, and see that they do have colors!

Color of a star is related to its wave properties.

Waves: 

In a puddle:

Q3: Which wave is moving faster? Both same.

Q4: What direction will the red dot in the water move? It will not move. 

Restoring force & mass dependent. 

Mass of water larger/ restoring force is larger. 

So depending on depth of the water.

In a rope: on tension / mass of rope.
 
 

Wave breaker near ocean with two openings.

Two waves meeting: (We will work on that on Wednesday again): Constructive & Destructive intereference.

"Junk piles" where waves come together near wave breakers.

Hand out "glasses"

Show laser light. "Junk piles" analogy.

Show white light. Wow. Note 2nd order rainbows, 3rd order, etc. 

Give out "glasses", Show pillars of light, barcodes of light.

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