Quarks to Cosmos Midterm 1

astronomical unit (AU)

distance between the sun and the earth

parsec

the distance at which a star subtends one second of arc in parrallax

Kepler's first law

planets move around the sun in ellipses, with the sun at one focus

Kepler's second law

the area swept out by a planet in any time interval is always the same

Kepler's third law

the period P of the planet is related to its semimajor axis a(roughly the same as the radius in our solar system) by:
P^2 = a^3

Newton's first law

Law of inertial bodies:
bodies in motion tend to stay in motion, bodies at rest tend to stay at rest

"uniform motion"

if a body's instantaneous velocity is constant, then the sum of the forces acting on the body are zero

Newton's second law

the rate of change of momentum of a body is proportional to the total force acting on the body

Newton's second law means...

force is required to change a body's momentum

Newton's third law

when one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body

Constructive interference

the waves add together to make a single bigger wave

Destructive interference

waves cancel each other and the wave goes away

Doppler Effect

if an emitter of sound is moving, the time between receiving successive waves will change. Thus, the frequency of the wave will change

Energy is...

proportional to the frequency of the wave

Frequency times _______ is the speed of the wave

wavelength

Redshift

When an object moves away from an observer, the light waves it emits stretch out, increasing the wavelength and decreasing the frequency of the light. This shifts the light towards the red end of the spectrum.

Blueshift

When an object moves towards an observer, the light waves it emits bunch up, decreasing the wavelength and increasing the frequency of the light. This shifts the light towards the blue end of the spectrum

Blackbody Spectrum

an object that absorbs all light that hits it

How are light and energy related?

-it's considered a form of energy
-The energy of light is directly related to its wavelength, with shorter wavelengths representing higher energy and longer wavelengths representing lower energy

formula for converting wavelength of light to energy

E = hc / λ

E: is the energy of a photon in Joules

h: is Planck's constant (approximately 6.626 x 10^-34 J·s)

c: is the speed of light (approximately 3 x 10^8 m/s)

λ: is the wavelength of light in meters

First thing to know about blackbodies

Blackbodies emit light at all wavelengths. It
may not be very much light when you get to
really high or really low energies, but there is a non-zero probability of light from 0 to infinity

second thing to know about blackbodies (wein's law)

The "peak" moves to the left as Temp goes up

third thing to know about blackbodies (stefan's law)

When the temperature goes up, the light emitted at ALL wavelengths goes up

absorption line spectrum

The exact wavelengths of the lines depends on the properties of the atoms in the
gas. Different atoms will create lines in different wavelengths
-COLD GAS, electrons get dropped

emission line spectrum

-same cloud of gas produces emission/absorption spectra

-all depends on which direction you're looking at the cloud

-off to the side, not at the source, you see emission
- HOT GAS, electrons get kicked up

where do the lines come from?

electrons moving energy levels

why are they lines?

when electrons jump to a different energy level, they emit a photo of light which creates a line in the spectrum

What is atomic physics that gives us the wavelengths (energies) of those lines?

-electron is not just a particle. It is also a wave
-it can orbit where the circumference is equal to an integer number of wavelengths

the sun is in a state of

hydrostatic equilibrium

"hydro"

behaves like a fluid

“static'“

does not change

"equilibrium"

a balance

where is energy in the sun generated?

the core

energy is transport through what in the sun?

photons through the radiation zone

process of energy generation for the sun

starts with four H atoms and ending up with 1 He atom releases energy in the form of a gamma ray

radiation zone

energy is transported by photons

convection zone

energy transported by hot gas bubbles physically moving (like boiling)

why is the sun stable?

-hydrostatic equilibrium
-pressure outtake matches gravity intake

how does expected lifetime change with stars of different masses?

as mass increase, the main sequence lifetime decreases

y-axis of HR diagram

luminosity or "absolute magnitude"

x-axis of HR diagram

stars "color"

main sequence of the HR diagram

a diagonal band of stars that stretches from the upper left corner (hot, luminous stars) to the lower right corner (cool,less luminous stars)

where are the giants/super giants on the HR diagram?

upper right (cool but bright)

where are the white dwarfs in the HR diagram?

lower left (dead stars with no fusion. only give off light because they are hot)

where are the pre main sequence stars in the HR diagram?

above and to the right of the main sequence

In both the pre-main-sequence evolution and the post-main-sequence evolution (ie, the giant phase) what is happening if a star changes luminosity without changing temperature (very much).

the total area goes up according to stefan's law

What is the general notion about how stars form?

stars form in clouds of gas that are denser than an average cloud of gas

Why is it that stars form in clusters?

because they originate from large, dense clouds of gas , where gravity pulls the material together in concentrated regions, causing multiple stars to form close to each other within the same area,

why do galaxies leave the main sequence?

when it significantly reduces its rate of star formation

why do galaxies' luminosities increase when they leave the main sequence?

they expand and become red giants

why do galaxies stop creating energy from fusion when they leave the main sequence?

they run out of hydrogen fuel in their core

what happens to galaxies' temperature and luminosity when they leave the main sequence?

its temperature generally decreases while its luminosity increases
-red giant phase

How do variable stars help us with the distance ladder?

by observing the apparent brightness and knowing its luminosity, astronomers can calculate its distance using the inverse square law

What is a globular cluster?

a spherical group of stars held together by gravity

how does a globular cluster's HR diagram change with time?

the cluster appears more "reddened" on the HR diagram as time passes

How do we age-date a globular cluster?

by using the HR diagram (measuring stars, plotting them,finding main sequence)

traditional way of dating a globular cluster

match the luminosity of the turnoff point on the cluster CDM

How do globular clusters tell us how old the universe is?

by studying the evolutionary stages of stars within these clusters, astronomers can determine their age