Midterm Flashcards
Astronomical Unit
The average distance between the Earth and the Sun
(1.5 x 10^8 km)
Parsec
The typical distance between stars as defined by the angular wobble caused by Earth’s orbit
(3.1 x 10^13 km)
Light-year
The distance light can travel in one year
(9.5 x 10^12 km)
Let’s reduce the size of the solar system by a factor of
10 billion; the Sun is now the size of a large grapefruit
(14 cm diameter)
How big is Earth on this scale?
A ball point
(100x smaller than the Sun)
Light travels at a finite speed of…
300,000 km/s
Speed
Rate at which object moves
speed= distance/time
(units of m/s)
Velocity
Speed and direction
Acceleration
Change in velocity
Units of speed/time
(m/s^2)
What is the acceleration of gravity on Earth?
10 m/s^2
Galileo showed that g is the (same/different) for all falling objects, regardless of their mass
same
Momentum
mass x velocity
What changes momentum, causing acceleration?
a net force
Angular momentum
The rotational momentum of a spinning or orbiting object
mass x velocity x distance from axis
Mass
the amount of matter in an object
Weight
the force that acts upon an object; depends on the acceleration of gravity
Newton’s 1st Law of Motion
An object moves at a constant velocity unless a net force acts to change its speed or direction
Newton’s 2nd Law of Motion
Force= mass x acceleration
Newton’s 3rd Law of Motion
For every force, their is always an equal and opposite reaction force
Kinetic energy
The energy of motion
= 1/2 m v^2
Radiative energy
The energy of light
Potential energy
Stored energy
Thermal energy
A measure of the total kinetic energy of all the particles in a substance
Depends on temperature & density
Temperature (energy)
Measures average kinetic energy of the many particles in a substance
The Universal Law of Gravitation
- Every mass attracts every other mass.
- Attraction is directly proportional to the product of their masses.
- Attraction is inversely proportional to the square of the distance between their centers
Fg= G (M1M2/d^2)
Newton’s Version of Kepler’s 3rd Law
(M1+M2)p^2=a^3
p= orbital period (yrs)
a= AU
M1+M2= sum of masses (solar masses)
Atomic Number
The number of protons in nucleus
Atomic Mass Number
The # of protons + neutrons
Molecules
Consists of 2 or more atoms
(H20, CO2)
Quantum Theory
Electrons in atoms are restricted to particular energy levels
In energy level transitions, what does jumping up or down cause?
Jump up= can occur by the absorption of a photon
Jump down= can lead to the emission of a photon of light
Wavelength
the distance between 2 wave peaks
Frequency
the number of times per second that a wave
vibrates up and down
The Electromagnetic Spectrum
Gamma rays S WL/ H F
X-rays
UV
Visible
Infrared
Microwave
Radio L WL/ S F
Continuous Spectrum
contains all wavelengths of light in a certain range
Emission Line Spectrum
the source emits specific wavelengths of radiation
Absorption Line Spectrum
dark lines or gaps in the spectrum corresponding to wavelengths that are absorbed by the gas
The Doppler Shift
Tells us only about the part of an object’s motion toward or away from us
Approaching us- smaller wavelength
Moving away from us- longer wavelength
Hydrostatic Equilibrium
Inward gravitational force= outward pressure changes
What does pressure depend on?
temperature and density
Core
Hot enough for nuclear fusion
Layers of the sun
Core
Radiation zone
Convection zone
Photosphere
Chromosphere
Corona
Solar Wind
Proton-Proton Chain
The Sun releases energy by fusing 4 hydrogen nuclei into 1 helium nucleus
What stays in the core and what is released as gamma rays?
Helium stays in the core
Energy is released as gamma rays
Radiation zone
Hotter and is relatively transparent
(energy flow by light)
Convection zone
Cooler and is more opaque
(energy flow by convection)
Convection at surface of the Sun
The visible top layer shows granulation with areas of rising gas surrounded by areas of sinking gas
Rising gas vs Sinking gas
Rising gas is hotter and brighter
Sinking gas is cooler and darker
Sunspots
Cooler than other parts of the Sun’s surface
Solar prominences
Erupt high above the Sun’s surface and caused by magnetic activity
Solar flares
Send fast bursts of x-rays and charged particles into space caused by magnetic activity
Coronal mass ejections
Send bursts of energetic charged particles out through the solar system
The Hertzsprung-Russel Diagram (HRD)
Plots the luminosity and temperature of stars
Distance from “spectroscopic parallax”
- Measure the star’s apparent magnitude m
and spectral classification - Use spectral classification to estimate luminosity (absolute magnitude M) from HRD
- Apply inverse-square law to find the distance
Magnitude version: m – M = 5 log d - 5
What 5 things does the H-R diagram depict?
Temperature
Color
Spectral Type
Luminosity
Radius
Luminosity
from brightness and distance
Temperature (stellar)
from color and spectral types
Star clusters
Groups of stars with the same age, distance, motions, and chemical composition
Open cluster
A few thousand loosely packed stars (Pleiades)
Globular cluster
Up to a million or more stars in a dense ball
Where do stars form?
In dark clouds of dusty gas in interstellar space
Interstellar medium
The gas between stars
Most of the matter in star-forming clouds is in the form of …
Molecules
(H2 and CO)
Interstellar dust causes background stars to appear…
fainter and redder
What passes through a cloud more easily than visible light?
Long-wavelength infrared light
What from a newborn star is often blocked by dusty clouds where the star is formed?
Visible light
Dust grain that absorb visible light heat up and emit…
Infrared light
Gravity can create stars only if…
it can overcome the force of thermal pressure in a cloud
Emission lines from molecules in a cloud can prevent a pressure buildup by converting thermal energy into…
Infrared and radio photons
Disks
probable birthplace of planets
Protostar
looks like a star but its core is not yet hot enough for fusion to take place
(baby star)
What leads to disks and jets?
Angular momentum of cloud
Main sequence star
Stars that are fusing hydrogen into helium
Degeneracy Pressure
Laws of quantum mechanics prohibit 2 electrons from occupying same state in same place
Brown Dwarfs
Starlike objects not massive enough to start fusion
Low mass stars
<2 solar masses
core helium burning, end up as white dwarf stars
Intermediate mass stars
2-8 solar masses
advanced nuclear burning, end up as white dwarf stars
Massive stars
> 8 solar masses
very advanced nuclear burning, become neutron stars, black holes, or worse
Stars become what 3 things after its time on the main sequence is over?
Larger, redder, and more luminous
Life Stages of a High-Mass Star
- Main Sequence: H fuses to He in core
- Red Supergiant: H fuses to He in shell around He core
- Helium Core Burning:
He fuses to C in core while H
fuses to He in shell - Multiple Shell Burning: Many elements fuse in shells
- Supernova leaves neutron star or black hole behind
H to He by the CNO cycle
High-mass main sequence stars fuse
H to He at a higher rate using carbon,
nitrogen, and oxygen as catalysts (helpers)
He fuses to C in core
Then He can fuse with C and heavier
atoms
Why is iron a dead end for fusion?
nuclear reactions involving iron do not release energy
Energy and neutrons released in a supernova explosion enable elements heavier than iron to form including …
Gold (Au) and Uranium (U)
