If you set a meeting with me outside office hours: Send Email & Its verified once I Email back. (Several cases of misunderstandings)

Monday: Help session, 7:30-9:30pm. If plans, come to 1st hour. Second hour answer questions.

Observations: Very few people came to Wednesday Obs. lab, the best day so far!  Remember 1/3 letter grade for missing ONE of the observation labs! (You may miss one afternoon lab without penalty, but that is not recommended either. We choose the best 7 out of 8).

Afternoon labs: Only people that had Dean's excuse to miss afternoon lab the 1st two weeks of classes: Makeup labs next thursday, Feb 17, 7:00pm.

Give back HW#2.

Handins: Formulas page. (Will be attached to exam 1, but learn to use it).

Regarding subject matter:
Note that we are slightly off the syllabus pace, due teaching chapter 24 before 26. (Basically weeks 4 & 5 were switched.)

The reason is the following: We are following the scientific method more rigorously: First we gather all the evidence, then we try fit a theory that will explain what makes the stars "tick". 

Evidence gathering: Today: HW#2 correction to formulas & solutions. Note that we are "mopping up" the Stefan-Bolzman Law (I=sigma T^4), not covered in class before: (On board, the I vs color graph).

Intensity is the power per area. I=P/A

I, the intensity, is the power (Watts) per unit area (m²).

 I=constant T⁴
 Already power per area!
Every unit area produces power of const x T⁴ , that's const x TxTxTxT !!!!

(the constant, named sigma, or s in the book pg. 366, is equal to 5.67 x 10^-8 Watt / (m² K⁴).)

Everything else as in now corrected HW solution page. 

On board: Two spheres, Big and Little. For problems 2-4. 
For problem 5: A sphere around the original star of 1.5 x 10^11 m radius to find I! 

Coming up next: The HR diagram and lives of star. Why do we think stars live turning a lot of m into E through
E=mc^2?

Which stars die young?

How can one find stars that are just being born?

What's in the "grave yard" of stars?

Tutorial solutions. Click here.