exam 1

sun is not on fire

true

19th century

past estimation of sun’s age

3,000-5,000 years

JJ Waterston

Meteoric Infall lead to meteors hitting the sun → heat energy

problems with JJ Waterson’s meteoric infall theory

1- lack of of enough meteor craters seen in sky

2- not enough meteor craters on earth

Lord Kelvin and Helmholtz theory

gravitational collapse & meteoric infall:

* sun shrinks every year
* shrinks → heat
* estimation: sun would last 32,000 years
* revised estimation: sun would last 30 million years

how old is earth? how do we know?

4\.5 billion years old

sedimintation

early predictions of earth’s age

1927: earth is 3 billion years

1940: 4.5 billion years

how old is the sun

10 billion years

sun’s composition

* 74% hydrogen
* 25% helium
* 1% metal

Arthur Holmes

* K-Arg Dating: used to date earth
* says earth is 370 million years old
* unaware of isotopes

half-life

time it takes for radioactive sample to decay by half

nuclear fission

splitting larger nuclei into smaller nuclei

nuclear fusion

combining two smaller nuclei to make one larger nuclei

energy mass defect

mass lost when combining smaller nuclei

mass lost during fusion transfers into energy

Arthur Eddington predicts…

* nuclear fusion in sun
* observes a variable star get bigger and smaller → eliminates gravitational collapse

Hans Bethe

* proton-proton chain (used by fainter stars)
* CNO cycle (most important nuclear reaction in brilliant stars)


* CNO > 1.3 Ms (mass of sun) > p-p chain

proton-proton chain

take 4 hydrogens → make 1 He

98% of what happens in the sun

CNO cycle

* carbon-nitrogen-oxygen
* used as a catalyst
* 2% of what happens in the sun

stellar nebula

giant cloud of gas in space

solar nebula

sun

catalyst for collapse in stellar nebula

1- supernova shockwave

2- passing dwarf galaxy

3- passing star

prostar to star

* when mass gathers in center, protostar will turn into a star with gas pressure and gravity
* has to sustain HYDROGEN nuclear FUSION

where does fusion take place in the sun?

core

hydrostatic equilibrium

balance between inward gravity and outward thermal pressure that prevents stars from collapsing

AU

* astronomical unit
* average distance between earth and sun

parallax

apparent shift in object due to a shift in viewpoint

stellar parallax

apparent shift in a star relative to distant background due to earth’s orbit around the sun

limit of parallax

\~326 ly = 100 pc (parsec)

stellar parallax equation

* D = 1 / p
* d is in pc
* p is in arcseconds

1 parsec is equal to how many light years

3\.26 ly

Friedrich bessel

1st person to use stellar parallax to determine distance to stars

inverse square law

brightness of a star is determined by its distance

* closer = brighter
* farther = dimmer

luminosity

power of a star emitted into space

* relies on surface temperature and size

apparent brightness

power / area of sphere (watts / m^2)

absolute magnitude

apparent magnitude if star was 10 pc away

apparent magnitude = magnitude scale

* 1st magnitude = bright star
* 6th magnitude = dim star
* sun = -26 (really bright)
* polaris = 1

spectrum of light

y rays, x rays, UV, color, IR, microwave, radio

* short wavelength -------------- long wavelength

absorption

electron absorbs light, jumps up in energy level

* small jump = small energy = red
* big jump = big energy = blue

emission

electron jumps down, emits light

* small jump = red
* big jump = blue

continuous spectrum

shows all colors

emission spectrum

few lines of colors

unique to each element

absorption spectrum

colors with black lines “missing”

Henry draper

* pioneer of astrophotography
* saw spectral lines of stars

Mary-Anne Draper

gives money to HCO (Harvard College Observatory) to honor Henry Draper (hubby) & continue astrophotography

Edward pickering

* HCO director
* uses $ to classify stars using pictures

Harvard computers

* all women
* paid half
* pictures taken of stars on glass plates
* use prisms on plates to analyze stars

Antonia Maury

own version of complicated classification and plushes work

williamina flemming

* In charge of classifying stars
* first publishers of classifying stars in Henry draper catalogue
* classification: alphabetical order & hydrogen lines
* A → stronger
* Z → weaker

Annie jump cannon

* FASTEST at classifying stars
* 350,000 stars total
* use OBAFGKM to classify

Cecilia payne

* england
* lecture by Arthur Eddington on solar eclipse
* 1st PhD in astronomy at Radcliff
* discoveries
* determines cannon’s classification scale was based on surface temperature
* all stars made of mostly hydrogen and some helium (published) = “what is the universe made of”
* never got full credit for ^ this discovery

harlow shapely

Payne’s advisor

Henry norris russell

* stars were though to be the same composition as earth
* made Payne put “probably not real” on dissertation
* credited discovery of “what universe if made of” even tho it was rly payne

star classification scheme

O, B, A, F, G, K, M

O star

hotter, bigger, blue

M

cooler, smaller, red

what type of star is the sun? color?

G2 star, green

B star

blue-white

A star

white (slight blue tint)

F star

white

G

white (yellow tint)

K star

orange-red

most stars in the universe are what classification? why?

M stars because they are the most efficient at burning hydrogen

what stars have longer life span?

cooler stars (such as M)