• An easy star to study because it is so close
• Pretty typical star
• Surface Temperature 5800K
• Diameter 1.4 X 10⁶ km (about 100 X the Earth)

92.0   %  atoms - Hydrogen

 7.8   %      "     - Helium

Trace elements: .03 Carbon, . 01 Nitrogen, .06 Oxygen, etc...

In the sun's core, 4H nuclei fused to form 1He nucleus

-4 protons -> 2 protons + 2 neutrons

Mass turned into energy according to

E = mc²

^{*5 million tons of matter converted to energy every second.}

• Need 6 Hydrogens to make cycle happen
• 6 Hydrogen going in
• 1 Helium 4 and 2 Hydrogen out
• 4 in 1 Helium out

The Sun will not burn forever

The solar core will fill with HE ash

Hydrogen fuel will be exhausted in 5 billion years

The Sun dies

• we look for the neutrinos (v)
• neutrinos (v) almost never interact with matter
• pass through a light year of Lead (Pb) and not hit anything
  
• Solar neutrinos (v) pass through the sun and out into the solar system
• neutrinos (v) apparent massless and travel at the speed of light

• 1000,000 gal of dry cleaning fluid in South Dakota Gold Mine
• Buried to avoid cosmic rays (1 mile deep)
• Because neutrinos (v) rarely interact, needed lots of dry cleaning fluid
• Looked for the reaction v and Cl (Chlorine) -> Ar (Argon)
• Observed only 1/3 the number expected

All wrong for various reasons:

• Neutrino (v) Oscillation
  - more than one type of neutrino (actually 3 types)
  - v may change form from one type to another
• Recent experiments to detect v oscillation
  - Super Kamiokande Experiment
  - Subbery Neutrino Canada

All of the sun's energy is made in it's core

How does the energy get out?

3 forms of transport:

Conduction

Radiation

Convection

Heat transported by direct contact between heated materials

• requires close contact between atoms
• stars are gaseous; conduction is unimportant

Radiation

Heat transported via em radiation

• principal means of heat transport in Solar interior. 
• photons absorbed and re-emitted in random directions.
• takes about 1 million years for photon to reach surface of the sun.

Heat transported by movement of heated material.

• Smoke goes up chimney (ex)
• part heated water
• Convection currents in stars important
• Convection currents transport energy to the surface and mix up stellar material.

[image]

• Center
• Core extends from center to about 200,000 km
• Temperature 15,000,000 K
• Defining Property: Energy generated by nuclear fusion

• 2nd layer extends from 200,000 to 500,000 km
• Temperature 7,000,000
• Defining Property: Energy transported by electromatic radiation

• Extends from 500,000 to 700,000
• Temperature 2,000,000
• Defining Property: Energy carried by convection

Hydrostatic Equilibrum

the visable surface of the Sun

• 
  defining property: EM Radiation can escape - the part of the sun we can see.

- light comes from the photosphere
- 500 km thick
- Convection Zone just below photosphere
- above photosphere gas is too thin to emit much light
(can see the light during a total eclipse of the sun)

-below photosphere the gas is too dense for light to escape (convection zone)

The photosphere has a mottled appearance referred to as granulation

• each granule appears as a bright spot surrounded by a dark area
• Granules are about 1000 km across (about the same sixe as Texas)
• The granules are due to the convection currents just below the photosphere
• Granules are constantly moving

directly above photosphere

defining property: Cool lower atmosphere

10,000 km thick

1/1000 as bright as photosphere - gas to thin to emit much light
-for a few seconds just before/just after totality it can be seen as a thin line of pink

spectrum of chromosphere taken during an eclipse

-chromosphere exhibits an emission spectrum
-Ha line gives it its pink color

- temperature ranges from about 10,000K at bottom to almost 10⁶ K at top

- density range 1/10⁴ to 1/10¹³ of air

solar atmosphere extending above chromosphere

defining property: Hot, low density upper atmosphere

can be seen during total eclipse of sun (blue halo)

Temperature- lower 500,000K, upper 3,500,000 K

• exhibits continuous spectrum from sunlight scattered from dust particles in corona
• emission spectrum produced by low density ionized gases
• density 1 to 10 atom per cm³
• hot gases in upper corona escape the sun's gravity and form solar wind.

solar wind

mostly made of ionized hydrogen which is just protons

defining property: Solar material escapes into space and flows outward through the dolar system.

the apparent shift of an object against a more distant background due to changes in the observers position

on earth when viewing a star at 6 month intervals, the baseline is 2 A.U.

above chromospere below corona

defining property: Rapid increase in temperature

• Galileo discovered them
• cool, dark features on solar surface
• last about 2 months
• dark because they are cooler than the surrounding photosphere
• Galileo used them to measure the suns rotation period (27 days)
• Associated with a large magnetic field
• The magnetic field disrupts the convection current below the photosphere  which causes the cooling
• umbrs (center) penumbra (outer)

• number of spots vary over 11 years period
• -0 to 100 spots
• 11 yrs max - 5 1.2 yr min - 5 1/2 yr max
• Maunder minimum between 1650 -1700 - during this time wx in England cooler than usual "Little Ice Age"
  Maunder minimum - practically no sun spots at all

• loops of gas ejected from an active region of the solar surface
• last about an hour
• consist of ionized gases trapped by magnetic field
• red color corresponding to Ha line
• can rise up to 500,000 km above solar surface

• violent eruptions on the solar surface
• last about an hour
• emit lots of x-rays, uv, light
• xrays and uv from flare will increase ionization of earth's upper atmosphere affecting shortwave radio and causing aurora borealis

The temperature of the Sun starts out at its core very hot approx 15,000,000 K as you go out towards surface, the  temperature decreases until you get to the photosphere, When you get to the chromosphere the temperature goes back up until you get away from the surface.

The parallax angle is one half the apparent shift in the stars position

one parsec = 3.26 ly

If a star has a parallax of 1 arc second its distance is 1 parsec

1/2 arc second = 2 parsecs    1/3 arc second = 3 parsecs

distance in parsecs = 1/parallax in arc seconds

If a star has a parallax of .25 arc seconds then

d = 1/.25 = 4 parsecs
d is about 13 ly (4X3.26=13.04)

The nearest star Centauri has a parallax of .76
d = 1/.76 = 1.3 parsecs
d is about 4 ly (1.3X3.26=4.2)

the apparent change in wavelength (frequency) of radiation due to the relative motion between the wave source and the wave observer.

ex: Police Car

Blue Shifted = the source approaches the observer, wavelength decreases/frequency increases

(i.e. high freq/small wavelength)

Red Shifted = the source moves away from the observer, wavelength increases/frequency decreases

(i.e. low frequency/long wavelength)

The greater the shift the faster the star is moving.

"Doppler can ONLY tell us the speed of an object along our line of sight"

due to the motion of a star across our line of sight

-over a period of time (many years) a star may change position slightly

speed of the star across our line of sight

we need both Transverse and Radial velocity to know the stars entire velocity in space

a Aquilae has proper motion of .662 arc sec yr

Bernard's star has the highest proper motion in the sky 10.3 arc sec yr

Transverse velocity can be calculated if we know the proper motion and the star's distance.

Hipparchus (2 century bc) classified stars according to their brightness into 6 classes.

1 brightest/6 barely visable

Astronomers have defined the apparent magnitude (m_v) scale based on Hippy's classification. However their scale does not stop at 1 it goes into negative numbers

ex: Sirius is -1.5  and Vega is 0

**The smaller the magnitude the brighter the star.

Difference in magnitude of 5 means a difference in brightness by a factor of 100

Each change in magnitude of 1 means a change in brightness by a factor of 2.51

ex: If star A has an apparent magnitude of 3 and star B has an apparent magnitude of 5

A is 2.51 X 2.51 = 6.3 times brighter than B

If A is 3 and B is 6 then 2.51X2.51X2.51 = 15.8 times brighter

how bright a star appears to us

It is not a measure of intrinsic brightness

sun = 26.7

Full Moon = 12.5

Venus = 4.4

Sirius = 1.5

a Centuri = 0

the apparent magnitude of a star if the star was 10 parsecs away

To calculate the absolute magnitude we must know the stars apparent magnitude and the distance.

*** Apparent Magnitude (m_v), Absolute Magnitude (M_v), Distance
If we have any two - we can calculate the third.

total amount of energy a star radiates in one second

energy radiated at ALL wavelengths

Measured in Watts

Suns luminosity is 4 X 10²⁶

^{a stars luminosity is usually stated in terms of solar luminosity}

ex 100 watt light bulb luminosity of 100 watts very little of the energy emitted from an incandesent light bulb is invisable light, only about 3% - Congress banned 100 watt light bulbs for that reason.

Two things determine a stars luminosity
Temperature and Surface area

*If we know absolute magnitude, we know luminosity

Because stars are approximate blackbody radiators (the hotter the bluer) we estimate a stars temperature by its color.

Red Stars =cool    Blue Stars = hot

We can measure a stars temp by observing the prominence of the Hydrogen Balmer Lines (lines visable to the eye)

stars are classified according to feature in their spectra

system of classification is about 100 yrs old. Annie Jump Cannon Harvard University.

Spectral class is desinated by letter and is indicative of a stars surface temp.

O B A F G K M

 (Oven Baked Apples From Grandma's Kitchen Mmmmm)

O = hotest  M= least hot

Each spectral class is subdivided into 10 sub classes
hotest to cold 0,1,2,3.....10

Sun is G2 star Surface temp 5800K

Class and SubClass of a star give accurate measurement of a stars surface temp.

an important diagram for understanding stars

HR = Herzsprung-Russell diagram

a plot of spectral classes on the x axis and luminosty on the y axis

each star has a point on the HR diagram, the location of the point is determined by the stars luminoisty and temperature.

X axis = Spectral Class or Temperature

Y axis = Absolute Magnitude or Luminosity

White Dwarfs= high temp, low luminosity

Main Sequence

Giants/Red Giants = cool, high lunminosity

Super Giants= cool, very large, high luminosity

Beatleguese is a super giant.

Near us = Red Giants few White Dwarfs.

[image]

• a method for determining a stars distance
•  
• uses HR Diagram
• It has nothing to do with parallax
• **If we know the apparent magnitude and the absolute magnitude/luminosity we can calculate the stars distance
• The HR diagram enables us to determine a stars luminosity or absolute magnitude.

Class                      Description

Ia                           Bright Super Giants

Ib                           Super Giants

II                           Bright Giants

III                          Giants

IV                          Sub Giants

V                           Main Sequence

WD                        White Dwarfs

Width of lines depends upon density of the suns photosphere. Density of photosphere is correlated with stars luminosity.

• Use luminosity to determine size.
• Luminosity is determined by 2 factors: temperature and size
• Know 2 and 3rd can be calculated.
  By determining the stars temperature and its luminosty we can determine the stars size

Antares= 500R (Supergiant)   Aldebaran= 40R

Capella = 15R,  Spica = 7R (Sub Giant)

Sirius= 2R/Sun 1R (main Sequence)

binary stars in which both can be seen seperately

Binary stars are resolved.

• after taking a number of measurements, we determine the "apparent relative orbit"
• Apparent because the orbit could be tilted at some random angle - tilted circle looks like an ellipse
• Relative because we have forced the bright star to be in the middle
• measure the orbit period of the binary
• measure the distance between the stars
• calculate the masses of the stars using Kepler's 3rd Law

Sirius is Binary A visual B not visable - 20 A.U. away fm each other
could be 40 A.U.

Correlation between a stars mass and its luminosity is called the mass luminosity relationship

the greater a stars mass the higher the luminosity

Mass luminosity relationship is ONLY TRUE for main sequence stars.

binary star system whose nature is revealed by its spectrum (too close to resolve)

lines in the spectrum move back and forth

as the stars move toward us - blue shifted

as the stars move away from us - red shifted

Capella (a Aurigae) is spectroscopic binary
45 ly - 104 day orbit - 160 L - G8III giant star, main sequence, lum class 4

Binary nature detected by variable in brightness

unresolved, orbit of stars seen on edge

as one star passes in front of the other, apparent brightness decreases due to eclipse

eclipsing binary stars are used for determining 2 stellar features: stellar mass and stellar radius

.O  Θ  O.  O .O  Θ

• The space between the stars is NOT a vaccum
• Gas and Dust between the stars
• Gas is mostly Hydrogen
• Interstellar dust grains not unlike cigarette smoke

Nebula - Nebulae plural

Interstellar cloud of gas and dust

3 types:

• Emission
• Reflection
• Dark

• emit their own light
• light comes from excited atoms
• atoms excited by radiation from nearby hot star(s)
• usually made of ionized hydrogen called HII region
• reddish color from HA line in Balmer
• some lines from ionized oxygen, OIII have a ugly greenish appearance

Reflection Nebulae

• emits light by reflecting light from nearby star
• dust specks in nebula reflecting light
• nearby star not hot enough to execute atoms in nebula
• often have bluish color
• blue color from dust grains, indicate size .003-1 mm

• dark
• do not emit light, do not reflect light
• detected because they block out light from background stars, nebulae

tips will become stars

Effects on starlight

Interstellar Reddnging

• stars appear redder than they actually are
• caused by IM preferentially scattering blue light
• light from distant star has lost some of its blue color and star appears redder
• ex: sunrise and sunset

• stars appear dimmer than they should
• IM absorbs some of the starlight
• like a very thin fog
• spectral lines of IM seen superimposed on stellar spectra

• em radiation emitted by cold neutral Hydrogen atoms
• atoms in ground state
• wavelength .21 cm
• important for mapping presence of neutral hydrogen

• H atom has 1 p and 1 e
• electron orbits proton
• both p and e rotates on its axis, spin
• e spin must be same as p spin or oppostie p spin
• when spins are in the same direction, energy of e is just a bit more than when spins opposite direction
• e can spin flip to lose energy and emit a radiowave proton
• SETI uses 21 cm radiation

Radio observations reveal presence of interstelar molecules

molecules emit distinctive wavelengths

molecules found include: carbon monoxide (CO), ammonia (NH3), formaldehyde (H2CO), and methelalcohol (CH3H) - like cigarettes