Ast 2hn23

THE SUN & STARS

Morgan George, Samantha Giddinge

What is the Sun made of? • It

is a huge ball of hydrogen and helium gas held together by gravity

• The

gasses get heavier and are more condensed was you move further towards the core

• GRAVITATIONAL

CONTRACTION: The contraction of the Sun when it was formed was slowed down by the energy that was being heated at its core

• ‘GRAVITATIONAL

EQUILIBRIUM: the reason the Sun’s core stays so hot is because the energy from nuclear fusion

• SOLAR

WIND: Charged particles from off the surface

• CORONA:

Outer most gaseous layer of the thin atmosphere of fast moving particles

• CHROMOSPHERE:

Middle layer of the atmosphere which is pinkish due to hydrogen emission

• PHOTOSPHERE:

The visible outer ‘surface’ of the Sun. It is so dense that it is all we see of the Sun

• CONVECTION

ZONE: Moving gases that cause bubbling (granulation) which looks like the surface is boiling

• RADIATION

ZONE: Hot, dense region where energy moves via protons

• CORE:

Hotter and denser where energy is made from nuclear fusion

Difference between Fusion and Fission Fusion

Fission

•A

• Smaller

bigger piece going into smaller pieces

pieces going into a larger piece

Nuclear Fusion and the Sun • Electrostatic

repulsion is overcome by a strong force – a nuclear biding force – taking over and forcing them together

In the Sun, four hydrogens bond with one helium to make energy. This occurs in a proton-proton chain.

How does heat leave the Sun? • Photons

are absorbed at the top of the radiation zone and this makes a tower of hot gas that moves the energy to the surface

• Granulation

is also occurring at this point due to the movement of particles

• It

sometimes takes over 100,000 years for a photon to reach the surface of the Sun because it bounces around so much

How do we know things about the Sun? • Just

like Earth, we learn through ‘sun quakes’ or observing neutrinos which are tiny particles with no charge and receive little to no interaction with anything and fly directly out of the Sun

• Doppler

is also used

Characteristics of a Star • LUMINOSITY:

Amount of power a star radiates per second

• APPARENT

BRIGHTNESS: Amount of starlight that reaches Earth – the energy per second per square meter • Depends on luminosity and distance

• How

are theses two related? • Divide luminosity by area to get the brightness

Laws of Thermal Radiation 1.

Hotter objects emit more light wavelengths

2.

Hotter objects emit light at shorter wavelengths

Stellar Spectrum • Dark

lines in a star’s spectrum correspond to a spectral type that reveals its temperature HOTTEST

COOLEST

O B A F G K M

Gravitationally Bound Stars • BINARY:

Two stars orbiting each other • Almost half the stars in the universe are binary

• Types • Visual • Eclipsing • Spectroscopic

Visual Binary • Stars

that we can directly observe the orbital motions of

Eclipsing Binary • Inclination

of the orbit is essentially zero making eclipses. The periodic eclipse implies the orbital period and the duration tells the radius

Spectroscopic Binary • Able

to find the orbit (period and velocity) by using and measuring Doppler shifts

Star Mass • Newton’s

version of Kepler’s 3rd law is that direct mass measurements are possible Only for stars in binary star systems

• Stellar

Sun

masses run from 0.08 to 150 times the mass of the

• BROWN

DWARFS: Objects that are less massive than 0.08 (discovered first in 1995)

High Mass •High

luminosity

•Short

lived

•Large

radius

•Blue

Low Mass •Low

luminosity

•Long

lived •Small radius •Red

*the Sun

Hertzsprung-Russell Diagram • Normal

stars that are burning hydrogen reside in the main sequence area

• Mass

goes up from lower right to top left

Star Clusters • OPEN

CLUSTERS: Several thousand stars, like the disk of the Milky Way

• GLOBULAR

CLUSTERS: Hundreds of thousands all packed tightly together found in the ‘halo’ of the galaxy

• Their

age is found from the main sequence turnoff point • The age is equal to the hydrogen burning lifetime of the hottest most luminous star that have not evolved into red giants