Download Astronomy Exam Notes.docx

Astronomy 2B03 Exam Notes/Practice:
Midterm Questions:
1. The star Betelgeuse is about 500 light years away from us. If this star underwent a supernova
explosion right now, how long would it be until we found out about it?
a) almost immediately.
b) 8 minutes.
c) 10 years.
d) 500 years.
e) 500 light years.
2. The expression "order of magnitude" corresponds to
a) one factor of ten
b) one factor of two
c) a factor of 2.5
d) two factors of ten
e) none of the above
3. The distances of nearby stars can be measured by observing their apparent motion as
a) the Earth orbits around the Sun.
b) the Earth rotates on its axis.
c) the Sun orbits around the center of the Galaxy. d) the planets cross their path.
e) they orbit the Sun.
4. If the Sun were suddenly replaced by a black hole of the same mass, the Earth would
a) remain in the same orbit.
b) move into a smaller orbit.
c) move off the current orbit in a straight line. d) be pulled into the black hole.
e) be burned to a crisp.
5. When you are on the top floor of a building, your weight is _______ when you are on the
ground floor.
a) much greater than
b) slightly greater than
c) equal to
d) slightly less than
e) much less than
6. What causes light from a star to be Doppler-shifted?
a) the distance between us and the star
b) the gas and dust between us and the star
c) the speed of the star toward or away from us
d) temperature differences between us and the star
e) the change in the speed of light as the star moves toward or away from us
7. We can detect the Doppler effect by
a) measuring the shift in distance of the star.
b) taking photographs six months apart.
c) measuring brightness.
d) measuring the shift in wavelength of a spectral line.
e) measuring the transfer of momentum to the interstellar medium.
8. Suppose the universe were not expanding, but was in some kind of steady state. How should
galaxy recession velocities correlate with distance? They should
a) be directly proportional to distance.
b) reverse the trend we see today and correlate inversely with distance.
c) show a scatter plot with most recession velocities positive.
d) show a scatter plot with equal numbers of positive and negative recession velocities.
e) none of the above.
9. Suppose the Hubble Constant were measured and found to be twice as large as it is now
believed to be. The maximum age of the universe in a Big Bang model would be
a) halved.
b) the same.
c) doubled.
d) squared.
10. From the spectrum of a star’s light we can learn
a) that all stars are made up of hydrogen, mostly
b) the numerical value of Planck’s constant
c) the numerical value of Hubble’s constant
d) the parallax of the star
e) none of the above
11. Galaxies
a) all have a spiral-like structure
b) are gradually shrinking under their own gravity
c) are gradually expanding by the action of Hubble’s Law
d) can be bigger than the Milky Way is
e) all of the above
12. Which of the following characteristics does NOT apply to giant elliptical galaxies?
a) rapidly rotating
b) low rate of star formation
c) lacking spiral arms
d) found in the centres of galaxy clusters
13. Compared to spiral galaxies, elliptical galaxies are
a) redder and rounder
b) bluer and rounder
c) bluer and flattened
d) redder and flattened
e) always much smaller
14. The age of the universe is
a) between 100 billion and 200 billion years
b) between 100 million and 200 million years
c) between 1 billion and 2 billion years
d) between 10 billion and 20 billion years
e) between 10 million and 20 million years
15. A spaceship moves by you at a high speed. Compared to how they would appear to you if
the spaceship were at rest, objects on the spaceship:
a) appear longer, and have greater mass
b) appear shorter, and have greater mass
c) appear longer, and have smaller mass
d) appear shorter, and have smaller mass
e) none of the above
16. Why should galaxy collisions have been more common in the past than they are today?
a) galaxies were more active in the past and therefore would have collided with each other more
frequently
b) galaxies were much bigger in the past since they had not contracted completely
c) galaxies were closer together in the past because the Universe was smaller
d) galaxies were more massive in the past
e) galaxy collisions shouldn't have been more common in the past than they are now
17. The Milky Way star Procyon is 11 light-years from the Sun while the Milky Way star Acrux is
320 light-years from the Sun. Hubble’s Law implies that: Procyon is moving at the same speed
as Acrux
a) Procyon is moving at the same speed as Acrux
b) Procyon is moving more slowly than Acrux
c) Procyon and Acrux are BOTH moving away from the Sun
d) bothb&c
e) none of the above
18. Which of the following is NOT an implication of Hubble's law?
a) the Universe is expanding
b) we are at the center of the Universe
c) the Universe had a beginning
d) the Universe was once denser than it now is e) none of the above
19. Rather than being a planet, Pluto is now considered to be a large member of
a) the Oort cloud
b) the asteroid belt
c) an extrasolar planetary system
d) the Kuiper Belt
e) the moon system of Neptune
20. During one lecture a thought experiment was discussed that involved a relativistic
skateboarder. The main point of the discussion was to show
a) that the speed of light is constant
b) that different observers could obtain different measures of time
c) that gravity and acceleration are equivalent
d) that light follows a curved path
e) none of the above
21. What important physics was demonstrated with the Photoelectric effect?
a) the speed of light is finite
b) metals are conducting
c) light has momentum
d) the speed of light is constant for all observers
e) blackbody radiation
22. Which of the following has the smallest wavelength
a) microwaves
b) ultraviolet light
c) visible light
d) gamma-rays
e) X-rays
23. The strong force is the force that a) drives nuclear decay
b) keeps planets in orbit around the sun
c) keeps light in a black hole
d) attracts electrons to protons
e) something else
24. Compare the light emitted by our Sun with that emitted from an identical distant star that is
receding from us.
a) the photons received on Earth from the distant star are less energetic
b) the photons received on Earth from the distant star have higher frequency
c) the photons received on Earth are the same from both stars except there are many more
from our sun
d) the photons from the distant star are bluer
e) not enough information to tell
25. Infrared light waves have __________ compared with visible electromagnetic radiation.
a) high energy and long wavelength
b) low energy and long wavelength
c) low energy and short wavelength
d) high energy and short wavelength
e) none of the above
26. According to what we learned about Hubble’s Law which of the following objects are moving
away from each other?
a) 2 galaxies in a galaxy cluster
b) you and the person in the seat next to you c) stars in the Milky Way
d) 2 isolated galaxies
e) all of the above
27. Which of the following is not a form of electromagnetic radiation?
a) radio waves
b) X-rays
c) electrons
d) sunlight
e) gamma-rays
28. Which of the following are correctly placed in order of decreasing distance (ordered from
furthest to closest) from here:
a) Alpha Centauri, Sun, Pluto, Andromeda Galaxy
b) Andromeda Galaxy, Alpha Centauri, Pluto, Sun
c) Andromeda Galaxy, Sun, Pluto, Jupiter
d) Alpha Centauri, Sun, Pluto, Jupiter, Moon, Toronto
e) Sun, Jupiter, Pluto, Moon, Toronto
29. Which colour of star is the hottest in temperature?
a) yellow
b) red
c) infrared
d) blue
e) green
30. Why would it be easier to measure parallaxes of stars from Pluto than from Earth?
a) Pluto is closer to other stars than the Earth
b) Pluto is colder than the Earth
c) Pluto is a dwarf planet
d) Pluto's orbit is larger than the Earth's orbit
e) Pluto's orbit is more stable than the Earth's orbit
Midterm from 2007:
1. Gamma rays travel
a. faster than c
b. slower than c
c. at speed c
d. at a speed depending on their energy
2. Which of the following is not a result of gravity?
a. the sun orbits the centre of the galaxy
b. jupiter orbits the sun
c. the earth orbits the sun
d. an electron orbits the nucleus
3. Which of the following is not one of the fundamental forces?
a. friction force
b. weak force
c. gravitational force
d. strong force
e. electromagnetic force
4. suppose you saw your friend passing by you at very great speed in a spaceship. you
notices a number of things about her and her spaceship. which of the following is false?
a. her clock was running slowly
b. her mass was smaller
c. her spaceship appeared to be shortened
5. a gedanken experiment was illustrated in class where an attempt was made to turn on
two lights at the same time. this was done to illustrate:
a. the speed of light is independent of the observer
b. the speed of light is independent of the sender
c. events that are simultaneous for one set of observes are not necessarily
simultaneous for another set
d. simultaneous events are always simultaneous
6. Arrange the following from the largest to the smallest; the nucleus, the atom, the proton,
a quark.
a. atom, nucleus, proton, quark
b. atom, proton, quark, nucleus
c. nucleus, atom, proton, quark.
d. atom, quark, nucleus, proton
7. suppose that a black hole and a normal star have the same mass. Suppose also that
they each have an earth- sized planet orbiting them at the same distance as the earth is
from the sun.
a. the black hole pulls harder on its planet than the normal str does
b. the normal star pulls harder on its planet than the black hole does.
c. the planet is suckes into the black hole.
d. the planets feel identical pulls
8. a theory of quantum gravity would be needed to understand
a. the universe at the instant of the big bang
b. the photoelectric effect
c. a relative skateboarder
d. how the earth orbits the sun
9. a quantum of light has
a. no mass and no momentum
b. no mass but it has energy
c. mass and momentum
d. mass and energy
e. no momentum because it is a wave
10. The CBR
a. alight from early universe
b. antimatter tunneling from black holes
c. big-bang nucleosynthesis
d. the radius of the cosmological horizon
11. matter curves space around it, which explains
a. the shapes of the spiral galaxies
b. gravitational lensing of distant galaxies
c. the photoelectric effect
d. the large look back times of distant galaxies
12. from the spectrum of a starts light we can learn about
a. the CBR
b. Planck's constant
c. the elements in the star
d. its lookback time
13. an electron in an atom can go to a higher, more energetic orbit by
a. absorbing a photon
b. emitting a photon
c. changing to a proton
d. emitting neutrinos
14. from hubble’s law we can deduce that
a. the earth and sun will gradually separate
b. we are at the centre of expansion
c. the CRB could tunnel into black holes
d. the universe may have a finite age
15. stars are made mostly of
a. carbon, nitrogen and oxygen from big bang nucleosynthesis
b. spectrum lines
c. black holes surrounded by helium gas
d. hydrogen from the early universe
16. The nearest star to our sun
a. have lookback times of a few years
b. are about as far away as jupiter
c. are too far away for parallax measurement
d. are obscured by the CBR
17. the equation E=mc^2 tells us that
a. mass m has energy equivalent to E
b. mass m has no energy if it is not moving
c. mass m has energy E if it is moving at speed c
d. the universe must expand
18. one consequences from E=mc^2 is that
a. redshifted photons are less massive
b. an object has energy E when it travels at speed c
c. photons can be converted to particles
d. the photoelectric effect can be create vacuum energy
19. the light from distant galaxies is redshifted because
a. they are moving through space
b. the wavelengths are stretched by the expansion of space
c. their lookback times are less
d. the stars in them are older at these lookback times
20. the early universe a few seconds after the Big Bang was
a. composed of stars but had no galaxies
b. has passed beyond our cosmological horizon
c. composed of helium gas, like stars
d. filled with hot radiation
21. the big bang
a. cannot be disproven as a scientific idea
b. created the earth 4.5 billion years ago
c. is the initial expansion of space
d. was the emergence of the solar system from a black hole
Sample Questions:
1. Our solar system is located in the
a) Milky Way's galactic halo
b) Milky Way's central nucleus
c) Milky Way's galactic disk
d) space between the Milky Way and its neighbouring galaxies
e) none of the above
2. The terrestrial planets are
a) Mercury, Mars, Earth, and Venus.
b) Jupiter, Saturn, Uranus, and Neptune.
c) Jupiter, Saturn, Uranus, Neptune, and Pluto. d) Venus, Earth, and Mars.
e) none of the above combinations
3. The four physical forces at work in the universe are gravitation, electromagnetic,
strong and weak forces. Which two of these are very short-ranged?
a) strong and electromagnetic forces
b) strong and weak forces
c) gravitation and electromagnetic forces
d) electromagnetic and weak forces
e) none of the above, the are all long range forces
4. From lowest frequency to highest frequency, which of the following correctly orders the
different categories of electromagnetic radiation?
a) gamma rays, X rays, visible light, ultraviolet, infrared, radio
b) visible light, infrared, X rays, ultraviolet, gamma rays, radio
c) radio, infrared, visible light, ultraviolet, X rays, gamma rays d) infrared, visible light, ultraviolet,
X rays, gamma rays, radio
e) radio, X rays, visible light, ultraviolet, infrared, gamma rays
5. Evidence of the expansion of the universe is shown by
a) The Einstein Cross
b) The 4.5 billion year age of the Earth
c) The abundances of the elements in stars
d) The redshifts of distant galaxies
e) time dilation
6. Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that
case,
a) Galaxy 1 must be twice as big as Galaxy 2
b) we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than
Galaxy 2
c) we are seeing Galaxy 1 as it looked at a later time in the history of the universe than Galaxy 2
d) Galaxy 2 must be twice as old as Galaxy 1. e) none of the above
7. A black hole and a normal star have the same mass. They each have an Earth-sized planet
orbiting them at the same distance as the Earth is from the Sun.
a) the black hole pulls harder on its planet than the normal star does
b) the two planets feel identical pulls
c) the normal star pulls harder on its planet than the black hole does
d) the planet is sucked into the black hole
e) none of the above statements are correct
8. Which of the following is not part of the official International Astronomical Union definition of a
planet? A planet ...
a) is close to round in shape
b) is a satellite
c) is in orbit around the Sun
d) has "cleared the neighbourhood" around its orbit e) none of the above
9. We can determine the distance to a galaxy that contains Cepheid variable stars by using
a) the period-colour relation
b) the mass-luminosity relation
c) the mass-radius relation
d) the period-luminosity relation
e) none of the above
10. Ann sees Bob travel by her in a very fast spaceship
a) Ann observes Bob’s clock to be running slowly and Bob observes Ann’s clock to be running
slowly
b) Ann observes Bob’s clock to be running slowly and Bob observes Ann’s clock to be running
fast
c) Ann observes Bob’s clock to be running fast and Bob observes Ann’s clock to be running
slowly
d) Ann observes Bob’s clock to be running fast and Bob observes Ann’s clock to be running fast
e) something else
11. Which is largest?
a)1.1 solar mass normal
b)1.3 solar mass white dwarf
c)2 solar mass neutron star
d)8 solar mass blackhole
Midterm Notes:
·
Dr. Parker is an observational astronomer
o
Galaxies and dark matter
·
Hierarchy of Universe:
o
Planets
o
Stars
o
Galaxies
o
Universe as a whole
Our Solar System
·
Size understanding
o
Moon=tennis ball, Earth = basketball
o
Sun =beach ball, Earth = marble
o
Massive planets are still much smaller than star (think Jupiter)
o
1 million Earths fit inside sun
o
900 Jupiters fit inside sun
o
50 Moons fit inside Earth
·
Terrestrial Planets: Mercury, Venus, Earth, Mars
o
have solid surface
o
may have atmosphere
·
·
·
·
·
·
·
·
·
·
·
·
Gas Planets
o
No solid surface
o
May have solid or liquid cores
The Earth
o
Land (terrestrial) + water, atmosphere, clouds, weather, temperature range
The Moon
o
Earth’s natural satellite
o
Rocky, ancient surface, airless, geologically dead, huge temp. Range
Mars
o
Terrestrial, “red” planet, cross between Earth and Moon
o
Old surface, some frozen water, thin atmosphere, geologically dead, potentially
habitable with help
Jupiter
o
King of planets (largest in our solar system)
o
Large ball of gas many “moons” (64 satellites) like a mini solar system
Saturn
o
Gaseous
o
Rings composed of ice, dust, small rocks
o
Many satellites “moons” (more than Jupiter)
Uranus
o
Gaseous
o
Cold
Neptune
o
Farthest “true” planet from the sun – 30 times farther from Sun than Earth is
o
Less noticeable rings
o
Space between Uranus and Neptune
Kuiper Belt
o
Lies beyond Neptune
o
Contains Kuiper Belt objects (KBO)
o
Includes Pluto and many other smaller asteroid-like objects
o
Pluto and other like objects (Eris) called dwarf planets
Definition of a Planet (IAU- International Astronomical Union)
o
In orbit around our Sun
o
Close to round in shape
o
“Cleared the neibourhood” around its orbit
o
Applies ONLY TO OUR SOLAR SYSTEM
IAU Definition of a Dwarf Planet
o
Is in orbit around the Sun
o
Is close to round in shape
o
Has NOT “cleared the neighbourhood of its orbit”
o
Is not a satellite- no moons
Small Solar System Bodies
o
Not round
o
Orbit around sun
·
The Sun
o
Center of our solar system
o
Typical star
o
Purely gaseous
o
Always activity on the surface
o
8 mins for light to reach Earth from Sun
o
Makes up 99.8% od the mass in our solar system
o
4.5 billion years old – expected to last 5 billion more years
o
Will get hotter as it grows older
§ Eventually burn away Earth’s life
o
Sun revolves around our Milky Way Galaxy every 225-250 million yrs
o
Located 25000 light years from our galactic center
Outside our Solar System
·
Average distances between stars = 1 million times the distance between our SS
planets
·
Parallax Effect
o
Used to measure distances to nearby stars
o
Effect of when you hold your thumb out and blink with each eye alternately and
object appears to move
o
Know how much it moves at distance X ,can figure out how far away it is by
how much it moves
o
Measure the change after about 6 months after carefully determining where in
space it was, and know how much the earth is moving
o
Can’t use for really far stars father stars – smaller parallax effect
o
Measured in Parsecs
·
Parsec
o
1 parsec = 3.3 light years
o
Nearest star (Alpha Centauri) is 1.3 parsecs (4 light years) away
·
Interstellar space
o
Space between stars in a galaxy
o
Contains raw, gaseous materials from which stars are composed
·
Galaxies
o
Stars are the building blocks of Galaxies
o
Galaxies are the building blocks of the universe
o
Billions of visible galaxies
o
We live in the Milky Way Galaxy
o
Up to 100 billion stars
o
About 80 000 light years
o
Eliptical, Spiral, dwarf and giant types of galaxies
§ Spirals
·
Flat rotating disks of stars,
·
gas and dust, visible spiral arms,
·
lots of new star (blue) formation in the spiral arms
§ Ellipticals
·
3-dimensional (not flat)
·
No visible spiral arms
·
Not much rotation
·
Not forming new stars
o
Generally found in groups
§ Large groups are called clusters (may contain up to thousands of galaxies,
trillions of stars)
·
Millions of light years across (star clusters are about 50 light
years across)
·
Weighs up to a trillion times the sun (star clusters are about 1
million suns)
·
Intergalactic Space
o
Space between galaxies
o
distances are about 1 million times larger than interstellar space
o
Measured in megaparsecs (millions of light years)
Theories of Astronomy/Physics
·
Lookback time
o
Time needed for light to travel to us from a distant galaxy
o
We see galaxies as they looked a long time ago
§ However, they are probably quite similar in their current states as stars
have lifespans of billions of years
o
Lookback time for stars in our galaxy are hundreds to thousands of years
§ Far away galaxies can be millions to billions of years away
o
Looking out in space, we look back in time-galaxies created within the first
billion years of the creation of our Universe
o
***Review Primer****
·
Universe Expansion
o
Stars and galaxies are getting farther from each other as time goes on
o
To prove, must measure the distance to other galaxies (can’t use parallax,
stars are too far away)
§ Must use Standard Candles
·
Standard Candles
o
Used to measure distance
o
Object has an intrinsic brightness
§ How much light you receive from it depends on how far away it is
o
However, measurements aren’t precise enough to see movement of planet
each year
o
The rate of motion of the galaxie is measured instead, using the Doppler Shift
of it’s light
·
·
·
·
·
·
·
Doppler Shift
o
Used to measure motion
o
If an object moves towards us we see a BLUESHIFT (SHORTER
WAVELENGTH)
o
If an object moves away from us we see a REDSHIFT (LONGER
WAVELENGTH)
o
We compare these shifts to the characteristic specrum lines of the dominant
element of the object to see how it is shifting and how much
§ Hydrogen and Helium are common
o
Spectrum acts are a “bar code”-possible to make very precise measurements
of movement!
o
Now can finally measure distance and motion of distance galaxies!
Hubble’s Law
o
Describes the relation between the motion of a galaxy and its distance from us
§ Speed measured by amount of Doppler Shift
§ Distance measured with standard candle technique
o
Speed is proportional to distance
o
V=Hd (velocity = hubles contant times distance)
o
The overall appearance of the universe should be changing with time
§ Galaxies get further apart as time goes on
§ Thus, as we look farther away (more lookback time) galaxies appear closer
together
o
The Universe may have had a beginning
§ Earlier times, galaxies much closer together
§ Rearrange equation and 1/H = 13 billion years ago
§ Therefore our Universe is about 13 billion years old
o
Distance between galaxies expands, not the galaxies themselves
§ Held together by gravitational forces
Space and Distance
o
Meter is based on the particular rod of metal kept under particular conditions
Time
o
A second is a measure of time
§ Defined as a certain # of vibrations of a cesium atom
Mass
o
Mass is the measure of inertia of an object
§ Greater mass=harder to accelerate
o
Measured in Kilograms
Speed
o
Speed is the distance travelled in a second
§ Jogger goes about 3m/s
o
C = speed of light
Distance Travelled
o
Speed multiplied by the time travelled
o
D-vt
·
Gravity
o
One of four basic forces of nature
o
HOWEVER VERY WEAK in comparison to other forces
o
Galaxies are kept in line by a combination of gravity between the stars and
motion of stars
o
10^-38 = smaller than force that causes nuclear decay, electromagnetic force
and the force that holds nuclei together
o
Gravitational forces are only large when large masses are involved
·
4 Dimensions?!
o
Can include time as a fourth dimension
o
Gravity may be larger in an upper dimension
o
Possibility of MANY more dimensions than what we see
Relativity
·
Theory of Einstein
·
Special Relativity
o
All observers should measure the same speed of light independent of how fast
they are moving
§ NOT intuitive (generally velocities are additive, like javlin throwing)
§ People moving away from each other think the other persons clock is
running more slowly
§ Not relevant at small speeds
o
Consequences of SR
§ Time dilation
§ Length Contraction
§ No absolute simultaneity
§ GPS technology , Cosmic rays detected (time dilation)
·
Normally, the speed measured for something depends on how fast the observer is
moving (NOT in special relativity)
o
Not true for speed of light
·
Speed of light (Special Relativity)
o
Speed of light is the same for all observers
o
Time passes differently depending on speed (however, change in speed needs
to be very large in order for this to take effect) = TIME DILATION
·
E=MC^2
o
All mass has energy
o
Mass times speed of light squared is the energy which a mass has
o
Therefore energy and mass are equivalent descriptions of something as they
are related by a CONSTANT
o
Mass would be infinite if it’s velocity was the speed of light
o
Increase in mass costs energy, decrease in mass releases energy
o
Given some energy, mass can be created
§ Uncertainty principle allows us to borrow energy for a short time
§ With this energy, matter can be created (electron + positron)
§ They self-annihilate and give the energy back
§ Therefore vacuums are not empty
·
General Relativity
o
All laws of nature are the same for observers moving in an arbitrary way
relative to one another
o
Makes the curvature of space a physical variable
o
No experiment performed in one place can distinguish a gravitational field from
an accelerated reference frame (rocket ship up ball drop vs ball drop on earth)
Gravitational lensing
·
Large mass between us and a distant galaxy gives us a distorted image of the galaxy
as light bends around the gravity of the mass
·
Gravity waves-not much evidence but gravity thought to move like waves (as
mass moves/is disturbed)
·
GR Includes:
o
Principle of equivalence
o
Gravitational redshift
o
Gravitational time dilation
o
Gravitational waves
o
Gravitational lensing
o
Curved space time
Space-Time
·
“world line” – line which represents distance per time, only in this case, distance
represented by X axis as the “dependent variable”
o
A world line lower than speed of light cannot exist on a graph of distance vs c
*time
§ Would indicate movement faster than the speed of light
·
Cannot move faster than the speed of light due to causality
o
No picture of how the future looks if information travels faster than the speed of
light
§ Cause MUST come before effects or Physics falls apart
§ Grandfather paradox-go back in time, kill your grandfather, you cease to
exist
·
Time advances more slowly for observers closer to a gravitational source (plane vs
ground)
·
Space time can be thought of as a fabric
o
Grid can be distorted or “warped”
o
Larger mass = larger gravitational force=more warping
§ Warping = gravity!
o
Light does not change direction, it follows the curvature of space
o
Tells matter how to move!
·
Black Holes
o
o
o
Quantum
·
Light
o
o
o
o
o
When energy of light goes to zero as it tries to leave a strong gravitational field,
black holes can form
Time appears to run slowly
Gravitational strength is the same as for a regular star of equal mass
§ Therefore NO SUCKING :D!
Behaves as a wave and a particle-duality
C=F*wavelength
Wavelength increases, f decreases
F increases, Wavelength decreases
When you run towards light, speed is contant but you encounter more crests ->
BLUESHIFT
o
Light bends very slightly due in gravitational field or accelerated reference
frame
·
Momentum
o
P=mv -> momentum = mass times speed
·
Quantum Mechanics
o
Newton’s laws break down when applied to extremely small distances (atomic)
o
Blackbody Radiation
§ Hot objects glow with a spectrum of colors that depend on temperature, not
composition
o
Plank-light energy comes in small quanta (chunks)
§ Einstein – Photoelectric effect came from this
o
Photoelectric effect
§ Light behaves as a particle (photons)
§ Light has momentum but no mass
o
Cannot measure momentum and position simultaneously, precisely.
§ Heisenburg’s Uncertainty Principle
§ Particle can’t have momentum and position simultaneously as a
measurement of 1 disrupts the other
o
Evidence for existence of quantum physics: black body radiation, photoelectric
effect, double slit experiment, quantum tunneling, spectral lines
o
Quantum in life: lasers, transistors, accuracy of atomic clocks, quantum
cryptography, fluorescence
Quantum Gravity
·
Combines general relativity and quantum mechanics
o
Large and small extremes
·
At small distances, quantum jitter is introduced, uncertainty principle is so big that
space time fluctuates a lot
·
Every particle exerts a gravitational pull on other particles
·
String theory
o
Small objects called string
o
o
Tidal forces
·
·
·
·
·
·
·
Vibration of sting gives an elementary particle
Strings are vibrating in 10 dimensions of space
In real gravitational fields the acceleration is NOT constant
Gravity pulls towards the Earth’s center
Tidal forces (ie tides which are affected by moon’s gravity)
You can tell you are in a gravitational field as opposed to an accelerated fram of
references if tidal forces play apart (dropped balls will fall towards the center of
gravity, rather than completely straight down)
Needed to explain extremely small scales
Visit Atoms primer on Avenue
Astronomical Research
Finding planets outside of our own solar system
o
The IAU “working definition” for extracellular planets
§ Objects with masses below the limiting mass for thermonuclear fusion (13
Jupiter masses) which orbit stars are “planets”
§ Minimum mass for a planet to be considered a planet should be the same
as in our solar system
·
If mass was larger than this it would be a star
§ Substellar objects with true mass above the limiting mass of thermonuclear
fusion of deuterium are “brown dwarfs” no matter how they were formed
or where they work
§ Cannot be free-floating
o
Summary, can’t be free floating, can’t be a star, must orbit a star
Planets are dim and hard to find in comparison to stars
o
Transit method for finding planets
§ Measure brightness of star for many weeks
§ If planet orbits on your side of the star, there will be a fainter amount of
light
§ However, the star light is not perfectly constant, so it can be difficult to see
if there is a real transition, or just “noise”
§ Don’t see the disk of the star, just a point of light
§ Need a large planet relative to the size of star
§ Must be “edge on” – meaning orbit must be aligned relative to you
§ Very difficult to measure
o
HAT-P-7 Light Curves
§ Satellite which collects images for transit method gets very clear results
o
Doppler (Velocity) Technique for finding planets:
§ uses the spectrum of the star to measure its speed of motion towards or
away from us
§ Changes cyclically as its planet orbits around us
·
Watch the star move back and forth around orbit by seeing the
cyclic change in the spectrum lines (light based on planets
velocity)
·
·
§ When planet moves from left to right, blue shift, right to left, red shift
§ The star and the planet each orbit around the center of mass of both of
them together
§ Decent telescope from earth can get a good Doppler shift
§ We see star is redshifted and blueshifted because of the planet
§ If there is a non-standard pattern to the shifts, then there are probably
other larger planets
§ *THIS IS THE PREFERRED METHOD*
·
What we are measuring is the period of the wave, and the
amplitude (how high is the blue and the red shift)
·
Tells us the orbital period
o
Longer orbital periods = large orbit
o
Amplitude tells us mass of planet
o
Lets us find out the period and the amplitude
·
Measurement is challenging- must find cyclic motions of just a
few meters per second (very precise)
·
Couldn’t be done until the 1990’s
·
Pioneered by a Canadian Astronomy team (mostly international
now however)
§ Jupiter is on a 12 year orbit and causes sun to experience a velocity
change of +/- 13 m/s
§ Jupiter-like planet in far away star orbits it’s sun in only 4 days! J
§ Roughly5 % of nearby stars have Jupiter-sized planets which are very
near their sun’s
§ Over 700 confirmed, 1200 candidates
§ There are currently 33 extra solar planet systems with up to 6 planets
around 1 star!
·
This 6 planet system is called Kepler 11
o
Doesn’t resemble our solar system
§ Lowest mass exoplanet found so far is 2 times larger than the Earth
o
Earth-like exoplanet found
§ Gliese 581d
§ 20 light years away
§ 7.8 times more massive than the sun
§ 0.25% radius of the Earth
§ First possible “habitable zone” planet found during the last year
Finding Earth-Like Planets
o
Planets found so far are large and very close to their star
o
Much harder to find smaller and farther planets from stars like EARTH J
Observing Smaller Planets
o
Must block out light from nearby star-or will override the light from planets
§ Can be done with a ground built telescope
o
Want to look for signs of life
§ Signatures of chemicals which we need to live
·
·
·
·
·
§ Oxygen
§ Atmosphere
o
Not able to study chemistry of far away planets
§ Have directly images, but not very well
·
Biased – large planets + large orbits easier to see
§ Infrared telescopes can see planets more easily than in the optical light
3 important methods for finding planets:
o
Direct imaging
o
Doppler (Velocity) Technique
o
Transit Method
Young stars
o
Have discs around them of matter
§ Planets are formed from this
Creation of LIFE!
Formation of Planetary Systems
o
Natural consequence of star formation
o
Piece of molecular clouds collapses into a disk
§ Stars form at center
§ Dust grains form and then come together to form rocky chunks
·
Chunks come together to make planets! (rocky)
§ Ice form at a larger radii – too hot when close to star
·
Gas giants are formed from ice cores
·
More material to form ices than rocks (thus giants)
·
Gas blown out of forming systems, but if some left when there
are ice cores, the ice cores can attract H and He, and make
planets like Jupiter and Saturn
o
Ice giants = large radii for formation
o
Terrestrial = close radii to sun for formation
Habitable Zone
o
Region of space where conditions are favorable for life (as we know it)
o
Must include liquid water
o
Atmosphere
o
Criticisms:
§ Life elsewhere could have different requirements than us
§ Other circumstances can make more distant planets habitable (volcanoes,
oceans etc)
§ Planets may migrate
Life on Earth
o
Not only arise, but survive
o
Connected to habitable zone
o
1.LOCATION
§ Liquid water
§ “Goldilocks” – not too hot, not too cold, JUSST RIGHHHTT :D
o
Habitable zone shifts outwards with time (sun gets hotter and brighter with
time)
o
In 1 billion years Earth will be too hot
o
2. TIMING
§ Life doesn’t happen quickly (evolution)
§ Need a star which lives for 4 billion years in order for life to evolve
§ Ideally want 9-10 billion year life span
§ Low mass stars will live longer
·
However, dimmer so have a smaller habitable zone
§ Binary (partner) stars not suitable generally
§ May have already wiped out life
§ Many planets may be too low mass at this time
o
3.ATMOSPHERE
§ Greenhouse gasses in atmosphere (CO2, H2O, N) hold in heat
§ Too little atmosphere (MARS) = larger temp swings
§ Too much atmosphere (Venus)= HOT all time
o
4. WATER
§ No water = no medium for OUR biochemical reactions =life
§ Too much water = no shallow continental shelves which are thought to be
important for rapid development
§ Was the early heavy phase responsible for sending water to earth through
comets?
o
5.GLOBAL CLIMATE ISSUES
§ Catastrophic changes in climate are possible
·
Snowball Earth episode aprox 500 years ago
§ If occurs for too long, we get glaciation
§ Ice reflects more sunlight and causes further cooling
§ Only reverses if geological changes in crust occur (volcano’s etc)
o
6.GIANT IMPACTS
§ Mass extinctions (dinosaurs +asteroids)
§ Severe disruption of food chain on both land and in ocean (dust cloud = no
sunlight=no photosynthesis)
§ May have caused a global firestorm
§ Asteroid was probably 10 km wide
Big bang – universe started out small and hot.
·
Foggy to transparent – key prediction.
o
Also, big bang nucleosynthesis, expansion…
Will the universe expand forever?
·
Balance between stuff in the universe vs energy in the expansion.
o
If more energy than gravity (matter), then expansion forever.
o
iF matter more, it might stop.
o
Dark energy complicates this.
Boomerang Balloon Project
·
CBR
·
Lots of matter - more blobs.
·
Very good evidence that we live ina universe that is spatially flat. And we have lots of
matter, but not so much that it will recollapse on itself.
We live in a universe that is expanding forever
1 thing that we haven’t spoken about – first fraction of a second.
·
So far – nucleosynthesis, CBR – predicted observed.
·
Today - less certain.
Inflation era of universe –topic of the day.
Not a fundamental part of the big bang but an addon
·
Inflation model 1980s.
·
Big bang 1950s
millionth of a second A.B
·
very soon – particles named different than before.
·
Few minutes old to 300,000 - fundamental particles were protons, nuetrons,
electrons.
·
now, there ar eno protons or neutrons. what exist are quarks – able to form very
early in the universe (fraction of second).
·
light constantly interacting w/ particles.
·
state of matter - quark plasma .
as time goes on, universe expands and cool – reaches temp where protons and nuetrons
will form.
after quark plasma, nucleosyntehsis and CBR.
ifnlation era – incomprehensibly small time after big bang.
·
First suggested in 1980. Theory not really worked out.
·
Like string theory – can develop theories, but have to be falsifiable and testable.
·
favoured theory for early universe.
not 4 fundamental forces, no particles -> false vacuum – at extreme energies, everything
exists in this state called the false vacuum.
·
No objects in the false vacuum, and theres no light, False vacuum looks like nothing.
·
there’s no stuff – just energy.
false vacuum - empty but filled w/ energ.
if you have lots of energy in a space, it has propensity to expand.
·
Built in springiness. Like the peanut box that comes out.
·
Coordinate system stretching.
·
early universe can expand faster than the speed of light.
o
Not a violation because it has no mass, so special realtivity okay.
today, can’t have expansion faster than c.
@ some point – some little piece of universe breaks off (bubble) for whatever reason
converts energy into mass (e=mc2).
·
When you do that, you can no longer be expanding faster than c.
·
bubble – where particles created. results in universe today.
·
1 little bubble turned e into m - that is OUR universe.
·
that it our universe at its earliest stages.
space grows exponentially quickly, and some piece becomes our universe.
region of space that we can see stuff – where light has had time to reach us.
·
Volume of space where time allowed light to reach us.
·
horizon – limit that we can see.
if part of the universe turns into our universe, what happened to the rest of space.
·
It is still in the false vacccum state.
·
So our universe is a bubble in a false vacuum.
·
Our visible universe ( is only a small portion of our whole universe)
Interesting implication – other universes could have formed bubbles.
inflation implies that tere are other universes out there.
·
No reason why other bubbles break off.
·
implies that there could be many universes.
·
because they are so vastly distant, no way to detect presence.
fundamental constants could be different in different universe.
·
Ours started out from the same seed, so it’s the same here.
having my parents live in some village and coming to see this prof running around the
floor speaking about different universe is quite comical.
·
naturally cynical.
Why Inflation?
·
Flatness problem –
why everywhere has same laws of physics.
·
Causally connected.
in 2 different direcitons, no reason why universe should be the same
·
w/ inflation, expect it to be the same.
monopole – magnet has n and s pole.
·
Should be objects that exist that have only 1. We don’t see them. We expect them to
exist. W/ inflation growing, rare objects become so rare that we don’t expect to see them.
·
flatness problem – cant just be a coincidence.
is inflation testable/falsifiable?
never forgetting to mention nobel prize.
false vacuum always growing larger than speed of lifht.
·
not possible for multiverses to interact.
Speed of light is independent of motion (observer)
·
Led Einstein to theory of special relativity.
Special Relativity:
·
1) If you’ve got people moving at different speeds, if they are moving at a constant
speed, the laws of physics will be the same.
·
Time must be observer dependent.
High-speed train thought experiment.
Person outside would see light at the back of the train first (wouldn’t be simultaneous
like before).
Another thought experiment – mirror and light source
·
Me sitting in my seat observing the light observe it to be longer than the skateboard
himself.
o
I think his clock running slowly, and he thinks my clock is running slowly.
Simultaneity does not exist for observers moving at different speeds.
"Moving clocks run slowly”
·
Effect size depends on speed.
o
Closer to speed of light, larger the effect.
We never detect relativistic effects because nothing in our earth really moves at the
speed of light or anywhere close it.
You cant tell which one is moving fast (A, B).
·
A thinks A is not moving and B is moving to the right.
·
B thinks B is not moving and A is moving to the left.
As an observer is moving quickly, his clock slows down – special relativity.
·
Experiments done w/ clocks.
·
Experiments done w/ particle physics.
2 main effects of special relativity:
·
1) time dilation
·
2) length contraction
·
3) in special relativity, there wont be AGREEMENT on SIMULTANEITY.
o
It will be RELATIVE, not ABSOLUTE.
Special relativity does affect our practical world.
·
GPS
·
Observing rays or some shit.
GENERAL POINTS FOR Special relativity – imp for speeds close to C.
·
Effects – time dilation and length contractiojn
EINSTEIN FEST
Energy and mass are equal descriptions of something (c is just a constant; it is “one”)
A tiny bit of mass multiplied by the HUGE C value means that a tiny bit of mass equal
ENORMOUS amounts of energy.
As you get to higher and higher ratios of speed of light (x axis (proportions of speed of
light)), gamma increases
·
EFFECT? Moving mass increases?? Don’t know
Ultimate Speed limit
·
neutrinos are the smallest massed particles in the universe?
·
we don’t know the mass – but the are massive (have mass)
o
really tiny though.
·
Neutrinos don’t interactor with stuff – light does.
o
That’s how they did the experiment.
Consider any reaction that causes a change in energy:
·
All reactions that occur in nature that involve an exchange of energy.
·
Increase in mass costs energy
·
A decrease in mass releases energy
E=mc2 – that’s why nuclear reaction so powerful
·
only need a little mass to create crazy amount of energy.
Modern definition of the metre.
·
Vs. the historic piece of metal sitting in France.
Mass – piece of metal sitting in France.
·
Defined by.
GRAVITY
4 fundamental forces of nature.
Strength of gravity:
·
Strong enough to kee moon in orbit around earth
·
Keeps galaxies together
o
Balance between gravity of mass and motions of the stars.
Gravity acts on short as well as really long ranges.
Is it a strong force (relative to other forces?)
·
The Big Crunch idea -> possible scenario for outcome of the universe (not the
favoured model).
·
It is strong - the big crunch has gravity at its base.
Gravitational attraction between neighbour and I are small.
·
Force is too small.
Other fundamental forces:
·
1) Strong force – only imp. on incredibly small scales
o
Keeping protons and neutrons in the nucleus -> keeps corks together.
o
*We are using strong force as our metric.
·
2) Electromagnetic force –
o
interaction of light w/ matter -> keeps atoms together
o
100x less strong than Strong force.
o
Infinite range.
·
3) Weak force – main importance in nuclear decay (fission processes).
o
Only force imp. for neutrinos.
o
Pretty weak
o
Significantly weaker than Strong force.
·
IMP. forces for atoms & molecules.
·
4) Gravity – force of attraction of one amass on another
o
Strength of gravity is extremely weak -> absolutely not. BUT, still really imp.
Numerator – product of 2 masses.
·
Distance.
Constant (g) real small – masses real large.
·
That’s why gravity becomes so imp.
Extra dimensions hint at the explanation of the force’s strength (g in particular).
·
We should consider ourselves living in a 3+1 dimensional system (we shouldn’t
separate space from time -> reasoning from relativity).
·
May be more dimensions of space.
·
Other dimensions might result in a small g.
String theorizes other dimensions.
Weight vs mass distinction.
G depends on distance -> diff. on mountains and sea level (measurable, we wouldn’t feel
shit (most likely).
Blackholes don’t suck.
·
Material that goes close may fall in, but they don’t suck.
Neptune inferred to exist because of its gravitational effect on Uranus.
·
Couldn’t see it with a telescope.
RELATIVITY – study of relative motion
Speed of javelin is larger relative to the ground if he runs.
Speed of light is constant for all observers.
·
Even if we run, it not going to “add up” like previous ex.
o
It is constant, and the same for all observers.
§ Counter-intuitive.
All electromagnetic radiation (light) moves at the same, speed of light…
When you are outside the train, you don’t see both sides lighting up at the same time.
·
Unlike the 1st example where it would light up the same for observers inside
(simultaneous)
·
Outside, it is not simultaneous.
Recent research (last day or two):
·
Discovery -> neutrinos (small massed particles) observed to move faster than light.
o
Given the distance (Italy to Switzerland [between 2 particle labs]).
o
Prof has spoken to other profs and they believe it can’t be true (there has to be
some error). The researchers said they were really conservative and cant find any errors.
o
Main criticism -> error of 10 nanoseconds (others believe it should be bigger)
o
Likely a systematic error, but if no one can explain this -> big finding.
o
60-80 nanosecond difference between light and neutrino speed (in the expt)
§ Everything in special relatively comes from the idea that nothing can travel faster than
c.
Main concept of last time – raisin bread shit.
Visible light is a tiny portion of all electromagnetic radiation in the universe.
Gamma Rays
·
Very energetic
·
Used in medical procedures
X-Rays
·
Still very energetic
Reason why UV light is damaging is because it is high energy.
Really long wave lengths -> radio waves -> transmitting communication.
Not expected to know the slide that has the vertical spectrum.
Gamma ray bursts – first detected by cold war
·
Nuclear bomb also gives off high energy gamma rays.
·
Soviets were pissed that Americans were testing, but it was really an astronomical
event.
X-Rays
·
Things that emit x rays are hot gas, AGN (active galactic nuclei) –x ray coming from
the centre of galaxies, they are associated w/ black holes.
UV
·
Young hot stars
Infrared we detect stuff with dust in the universe.
·
We use all different cameras for all the spectrum wavelengths.
Radio - 21-cm radiation
·
Atomic (neutral) hydrogen dominates the universe, but we cant normally see it. Only
at this wavelength.
Back in the day, we only had the ability to detect it only at the visible spectrum.
·
Now, we got the technology to look at all spectrum light.
Earth’s atmosphere can only take in certain wavelengths:
·
100% (atmospheric opacity) -> no light gets through (0% all gets in) – atmosphere
doesn’t allow these parts of the spectrum.
o
We would get cancer and radiation and shit.
o
Our atmosphere lets visible light through - > infrared, some gets through and some
don’t.
o
Radio waves get through.
§ Remember this is radio LIGHTwaves -> not radio audiowaves.
(Picture of all the wavelengths)
You see diff. features in diff. wavelengths.
·
In optical (visible) – you see a dark band
·
In others, you can see through the dust.
In astronomy, we only take greyscale pictures.
RGB pictures;
·
We take pictures at a particular light spectrum (for example, only at red light) – we
detect a greyscale image (its not colour, never is)
·
Then we take one that’s between red and blue (in between), and then we take ones
that blue (in the blue spectrum).
·
We assign colours to the greyscale and then we add them up, and then we get a
colour.
·
The image added up is similar to what our eye would see but not identical (our
receptors will create some variation)
The psychedelic picture on the next slide is just a compilation of different pictures taken
at different wavelengths and then compiled.
that’s what we do w/ our pictures -> we take many and then compile them! The significant
portions of each dominate that portion on the master copy.
In the centre of the galaxy, there is an AGN and shit is falling into the black hole and then
it gashes out (the gash spreads so far that it is like as far as the galaxy itself)
You cant get small pixels from observations on the ground (on earth). If we take pictures
of outer space we get to see much more.
·
Atmosphere blurs the picture and shit.
Subaru telescope – huge, owned by the Japs. Sits in Hawaii.
·
One of the best on the earth.
·
The Hubble telescope is better resolution, obviously.
Meter – rod of metal held in Paris under controlled conditions.
Time – seconds come from the number of vibrations in a cesium atom.
Light Beams
·
Right – travelling (+)
·
Left – travelling (-)
·