Welcome to Phys333-16S

Course Instructor: Prof. Stan Owocki205 Sharp Lab(302)831-8357astroprof@bartol.udel.edu

Fundamentals of Astrophysics

Course Theme

• The physical laws and forces that govern our lives...–  e.g. gravity, electricity & magnetism, nuclear binding

•  Also govern the cosmos...–  planets, stars, galaxies, even the universe itself

• Use geometry, logic, physics, & math to:–  quantitatively determine the physical properties of

astrophysical objects, e.g.– Stars, Clusters, ISM, Galaxies, Gal. Clusters, and

ultimately, the Universe and “Big Bang”!

- Albert Einstein (1879-1955)

"The most incomprehensible thing about the universe is that it is comprehensible."

AstroPhysics

• Based on a triad...–  observations (mostly of light)–  theory (physical laws)–  computation (by hand and computer)

Why am I taking this class??

Should I take this class?

Science & Math Disclaimer

• This is a Quantitative Science course• Language of Science is Math• Science of Astronomy is Astrophysics–  Not just “Descriptive” Astronomy”

• Mostly use “freshman physics” (Phys207/208) and calculus

• But also some (basic) Quantum and Relativity• LOTS OF COMPUTATION, –  e.g. HW, Class, Exams

Chinese ProverbI hear

and I forgetI see

and I rememberI do

and I understand

So to learn by doing...

• HW problems– Work with others ok– But must be open, acknowledge• i-clicker quizzes, in class

exercises•  Class participation– Ask questions. Engage!

Course web page

http://www.bartol.udel.edu/~owocki/phys333

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Syallabus• 1 mid-term (20%) + 1 final (30%)• HW 20%: about one set a week,–  due classtime on date; NO LATE –  drop lowest HW in final grade

•  class participation 15% (i-clicker ~ 10%)•  term paper/project 15% (details later)• Any questions??

Assignment for Thursday–  Review the course Syllabus–  Read secs. 1-3 of DocONotes-Stars1.pdf–  Be prepared to answer Quick Questions for sec. 2 –  Look over website: http://scaleofuniverse.com/

–  view movies on “Powers of Ten” & “Most Astounding Fact”–  play with “scale of the universe” app

3 basic observables for stars

• 1. position on the sky• 2. apparent brightness• 3. color or spectrum

• From this, we can infer physical properties:–  distance, size, temperature, mass, age, luminosity, etc.

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QQ1: a. An astronomer living on the equator watches two stars pass directly overhead (i.e. through the local "zenith"), with a clock time difference of 1 minute. 

- What is the declination of the two stars (in degrees)? - What's their difference in Right Ascension?

- What is the angular separation of the two stars on the sky (a.k.a. celestial sphere). Give your answer in degrees?

0o

1 min

1/4 o

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QQ1: a. An astronomer living on the equator watches two stars pass directly overhead (i.e. through the local "zenith"), with a clock time difference of 1 minute. 

- What is the declination of the two stars (in degrees)? - What's their difference in Right Ascension?

- What is the angular separation of the two stars on the sky (a.k.a. celestial sphere). Give your answer in degrees?

- But appearing close in the sky, does NOT mean two stars are physically close!

0o

1 min

1/4 o

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An astronomer living on the equator watches two stars pass directly overhead (i.e. through the local "zenith"), with a clock time difference of 1 minute. 

What is the angular separation (in degrees) of the two stars on the sky (a.k.a. celestial sphere).

A.  1 degree

B.  4 degrees

C.  ¼ degree

D.  ½ degree

E.  There is insufficient information to answer

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An astronomer living on the equator watches two stars pass directly overhead (i.e. through the local "zenith"), with a clock time difference of 1 minute. 

What is the angular separation (in degrees) of the two stars on the sky (a.k.a. celestial sphere).

A.  1 degree

B.  4 degrees

C.  ¼ degree

D.  ½ degree

E.  There is insufficient information to answer

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How to infer distance

•  In every day world, we use two methods:–  angular size assuming physical size–  stereoscopic vision

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Size Illusion

Angular size, distance, & parallax

•  How do we infer distance?

1.  Decline of angular size for a given fixed size

2.  Stereoscopic eyes -- bending angle

How to infer distance

•  In every day world, we use two methods:–  angular size assuming physical size–  stereoscopic vision

•  In astronomy we formalize this via–  angular size = physical size / distance• a = s/d

–  trigonometric parallax• d = s/p 24

Angular size

a D s�

a = 360° s2πD

s a = 360o ______ 2π D

Class Example

a D

At distance D = 6 paces ~= 4 m

Person of size s = 2 m

Angle a = 360 2/(2π 4) = 90/π = 30o

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sin α2

⎛⎝⎜

⎞⎠⎟=Rd

for α << 1, α 2R

d

Parallax

aD

sa

s

For earth’s orbit with size/radius s =1 au, then a (in arcsec) represents the parallax angle to an star/object at distance D in parsec (pc).

*

s/auD/pc = ______ a/arcsec

1D/pc = ______ a/arcsec

Assignment for Thursday–  Review the course Syllabus–  Read secs. 1-3 of DocONotes-Stars1.pdf–  Be prepared to answer Quick Questions for sec. 2 –  Look over website: http://scaleofuniverse.com/

–  view movies on “Powers of Ten” & “Most Astounding Fact”–  play with “scale of the universe” app