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sun is not on fire

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1

sun is not on fire

true

19th century

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2

past estimation of sun’s age

3,000-5,000 years

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3

JJ Waterston

Meteoric Infall lead to meteors hitting the sun → heat energy

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4

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

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5

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

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6

how old is earth? how do we know?

4.5 billion years old

sedimintation

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7

early predictions of earth’s age

1927: earth is 3 billion years

1940: 4.5 billion years

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8

how old is the sun

10 billion years

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9

sun’s composition

  • 74% hydrogen

  • 25% helium

  • 1% metal

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10

Arthur Holmes

  • K-Arg Dating: used to date earth

  • says earth is 370 million years old

  • unaware of isotopes

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11

half-life

time it takes for radioactive sample to decay by half

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12

nuclear fission

splitting larger nuclei into smaller nuclei

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13

nuclear fusion

combining two smaller nuclei to make one larger nuclei

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14

energy mass defect

mass lost when combining smaller nuclei

mass lost during fusion transfers into energy

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15

Arthur Eddington predicts…

  • nuclear fusion in sun

  • observes a variable star get bigger and smaller → eliminates gravitational collapse

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16

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

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17

proton-proton chain

take 4 hydrogens → make 1 He

98% of what happens in the sun

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18

CNO cycle

  • carbon-nitrogen-oxygen

  • used as a catalyst

  • 2% of what happens in the sun

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19

stellar nebula

giant cloud of gas in space

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20

solar nebula

sun

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21

catalyst for collapse in stellar nebula

1- supernova shockwave

2- passing dwarf galaxy

3- passing star

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22

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

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23

where does fusion take place in the sun?

core

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24

hydrostatic equilibrium

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

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25

AU

  • astronomical unit

  • average distance between earth and sun

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26

parallax

apparent shift in object due to a shift in viewpoint

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27

stellar parallax

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

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28

limit of parallax

~326 ly = 100 pc (parsec)

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29

stellar parallax equation

  • D = 1 / p

  • d is in pc

  • p is in arcseconds

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30

1 parsec is equal to how many light years

3.26 ly

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31

Friedrich bessel

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

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32

inverse square law

brightness of a star is determined by its distance

  • closer = brighter

  • farther = dimmer

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33

luminosity

power of a star emitted into space

  • relies on surface temperature and size

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34

apparent brightness

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

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35

absolute magnitude

apparent magnitude if star was 10 pc away

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36

apparent magnitude = magnitude scale

  • 1st magnitude = bright star

  • 6th magnitude = dim star

  • sun = -26 (really bright)

  • polaris = 1

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37

spectrum of light

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

  • short wavelength -------------- long wavelength

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38

absorption

electron absorbs light, jumps up in energy level

  • small jump = small energy = red

  • big jump = big energy = blue

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39

emission

electron jumps down, emits light

  • small jump = red

  • big jump = blue

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40

continuous spectrum

shows all colors

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41

emission spectrum

few lines of colors

unique to each element

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42

absorption spectrum

colors with black lines “missing”

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43

Henry draper

  • pioneer of astrophotography

  • saw spectral lines of stars

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44

Mary-Anne Draper

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

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45

Edward pickering

  • HCO director

  • uses $ to classify stars using pictures

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46

Harvard computers

  • all women

  • paid half

  • pictures taken of stars on glass plates

  • use prisms on plates to analyze stars

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47

Antonia Maury

own version of complicated classification and plushes work

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48

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

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49

Annie jump cannon

  • FASTEST at classifying stars

  • 350,000 stars total

  • use OBAFGKM to classify

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50

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

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51

harlow shapely

Payne’s advisor

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52

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

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53

star classification scheme

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

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54

O star

hotter, bigger, blue

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55

M

cooler, smaller, red

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56

what type of star is the sun? color?

G2 star, green

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57

B star

blue-white

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58

A star

white (slight blue tint)

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59

F star

white

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60

G

white (yellow tint)

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61

K star

orange-red

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62

most stars in the universe are what classification? why?

M stars because they are the most efficient at burning hydrogen

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63

what stars have longer life span?

cooler stars (such as M)

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