{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

lecture4

# lecture4 - Lecture 4 From Light to Stellar Properties...

This preview shows pages 1–15. Sign up to view the full content.

Lecture 4: From Light to Stellar Properties

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Think/Pair/Share Planet Zork's star emits most of its radiation at a wavelength twice as long as the Sun's peak wavelength, about 1 micrometer. What can you conclude about the temperature of Zork's star? A. Twice the temperature of the Sun B. Same temperature as the Sun C. Half the temperature of the Sun D. Not enough information to tell
Think/Pair/Share Which star is hotter? A. Star A B. They are the same temperature. C. Star C D. Not enough information to tell

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Think/Pair/Share Which star is hotter? A. Star A B. Star B C. They are the same temperature. D. Not enough information to tell
Think/Pair/Share Which star is larger? A. Star A B. They are the same temperature. C. Not enough information to tell D. Star D

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Why not just measure the sizes of stars directly? O (observer) Star or nebula or galaxy distance width angle θ Good approximation for astronomy (because θ is typically so small): width = distance* θ
Rough Angular Size of Stars (other than Sun) angle = diameter/distance diameter = 700,000 km or 7 x 10 8 m (assume Sun is typical) say distance = 100 lt-yr or 10 18 m angular size = 7 x 10 -10 radian or 4x10 -8 deg or 0.0001” (arcsec) cannot be resolved with current telescopes (0.1” is best we can do with Hubble Space Telescope (HST)) => For most stars, size can only be inferred from the Stefan-Boltzmann law!

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Think/Pair/Share Which star is larger? A. Star A B. Star B C. They are the same size. D. Not enough information to tell
Rank from least to most luminous Temperature key: Sizes and temperatures: A. D,B=C=E,A B. D,B,C,E,A C. A,E,C,B,D D. B=D,C,A=E E. None of the above

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Stefan-Boltzman law relates: surface area luminosity temperature I f we know any 2 of these quantities, we can infer the third. Temperature can (in principle) be measured using ______ law. Can surface area and luminosity be measured?
Inverse-Square Law

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Measuring Luminosity with the Inverse-Square Law f=L/4 π d 2 where: f is apparent brightness (power per unit area captured by your telescope), aka intensity or flux d is distance to the star We need to know the distance to the star to infer the luminosity!
Example: Sun

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Sanity Check: the Sun if the Sun is a thermal emitter, we can also compute L sun a completely different way...
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern