Final exam
Astronomy 1120 with Hornstein at University of Colorado Boulder
About this deck
By: Jamie Anderson
Textbook:
Cosmic Perspective, The (5th Edition)
Essential Cosmic Perspective, The (5th Edition)
Created: 2011-04-29
Size: 93 flashcards
Views: 84
Textbook:
Cosmic Perspective, The (5th Edition) Essential Cosmic Perspective, The (5th Edition)Created: 2011-04-29
Size: 93 flashcards
Views: 84
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Lookback time
o The farther we look in distance, the further we look back in time
Light-year
o Speed= distance/time, Distance= speed X time o The distance that light can travel in 1 year which is about 9.46 trillion km
Scale of the solar system
o Consists of Sun and all the objects that orbit it: the planets and their moons, and countless smaller objects including rocky asteroids and icy comets o It is often applied to other star systems o Size: 1010 km which is about 60 AU
Electromagnetic spectrum
o The complete spectrum of light, including radio waves, infrared light, visible light, UV light, X-rays, and gamma rays
Wavelength, frequency
o Wavelength: the distance between peaks of a wave o Frequency: The rate at which peaks of a wave pass by a point, measured in units of 1/s often called cycles per second or hertz
Photon
o little bundles (bullets) of energy
Spectral lines
o Bright or dark lines that appear in an object’s spectrum, which we can see when we pass the object’s light through a prism-like device that spreads out the light like a rainbow
Kirchoff's laws
o A set of rules that summarizes the conditions under which objects produce thermal, absorption line, or emission line spectra. o 1. An opaque object produces thermal radiation o 2. An absorption line spectrum occurs when thermal radiation passes through a thin gas that is cooler than the object emitting the thermal radiation o 3. An emission line spectrum occurs when we view a cloud of gas that is warmer than any background source of light
Emission line spectrum
o Most common visible light emission line: Hydrogen alpha o Emission for thin, hot gas: gas glows in specific colors § Colors represent electrons “falling down” energy levels § This is a fingerprint of the elements in the gas § No two elements have the same emission spectrum § The universe is mostly red
Absorption line spectrum
o Hot object viewed through cooler gas: dark lines on top of a rainbow § Gas can only absorb photons of the bright energies to move electrons to excited states
Continuous line spectrum
o Also called blackbody or thermal spectrum o The spectrum of an ordinary (incandescent) light bulb is a rainbow of color. Because the rainbow spans a broad range of wavelengths without interruption, we call it a continuous spectrum. o Hot solids (or dense liquid): emit a continuous rainbow of light
Parallax
o Helps measure distance: measure the apparent movement of stars over a year § Apparent movement is caused by Earth’s actual movement around the Sun o New distance unit invented for just this method of distance measurement § Parsec: (parallax-arcsecond) § An object at a distance of one parsec has a parallax of 1 arcsecond o Distance (parsecs): 1/p (arc sec)
Parsec
o The distance to an object with a parallax angle of 1 arc second; approximately equal to 3.26 light years
Reflecting telescopes
o Largest: Keck telescopes (10m) o A mirror only needs a high-quality surface coating, the rest of the glass doesn’t matter o Surface can be recoated as necessary o Newest telescopes use multiple smaller mirrors o Uses a precisely curved primary mirror to gather light. § This mirror reflects the gathered light to a secondary mirror that lies in front of it § The secondary mirror then reflects the light to a focus at a place where the eye or instruments can observe it
Refracting telescopes
o Largest: Yerkes (1m) o Big lenses are heavy o Lenses focus different colors of light at different places o Operates much like an eye using transparent glass lenses to collect and focus light. o The earliest telescopes, including those that Galileo built, were refracting telescopes.
Angular resolution
o Diffraction limit is proportional to wavelength/distance o The angle between two objects that can be seen as separated o Smaller is BETTER o High resolution= small angular resolution o Telescopes that are larger are capable of taking images with greater detail
Diffraction limit
o Best angular resolution a telescope can get § 2 points are just barely able to be recognized o Measured in arc seconds § 60 arcminutes in a degree o Better (smaller) for shorter wavelengths or larger telescopes
Light gathering power
o LCP is proportional to area o A telescope is a photon bucket collecting photons from the sky § Bigger bucket= more photons o The larger the telescope diameter, the more light rays it intercepts (larger area) o To make up for light collecting power you could just take longer images (Time= 1/diameter) o Telescopes that are larger are capable of taking images with greater detail
Interferometry
o Join multiple telescopes together to simulate one large telescope.
Adaptive optics
o Use a laser to create an artificial star and correct for the distortion caused by the Earth’s atmosphere § If you bounce the incoming light off a “deformable mirror” the light comes off corrected o Its like reversing the effect of a funhouse mirror
Absolute luminosity or absolute magnitude
o Based on putting all the stars at a common distance (a measure of the stars luminosities) o A measure of an object’s luminosity; defined to be the apparent magnitude the object would have if it were located exactly 10 parsecs away
Apparent luminosity or apparent magnitude
o Based on the apparent brightness (how bright they appear to our eyes) o A measure of the apparent brightness of an object in the skiy
Inverse square law of brightness
o An object’s apparent brightness depends on its actual luminosity and the inverse square of its distance from the observer o Apparent brightness: luminosity/4pi X (distance2)
Spectral type
o OBAFGKM o A way of classifying a star by the lines that appear in its spectrum; it is related to surface temperature o O is hottest, M is coolest
Luminosity class
o I to V o A category describing the region of the H-R diagram in which a star falls o Luminosity class I represents supergiants o III represents giants o V represents main-sequence stars o II and IV are intermediate to the others
Stefan Boltzman law
o Brightness of hot, solid objects o Hotter objects emit more light at all wavelengths per square meter of surface area o Intensity is proportional to temperature4
Wien's law
o Colors of hot, solid objects o Hotter objects peak at bluer wavelengths (photons with a shorter wavelength, higher frequency, and higher average energy) o Length of peak is proportional to 1/temperature (if temp goes down, peak wavelength up, frequency down)
Gravitational equilibrium
o High pressure created by fusion at center o Pull of gravity = push of pressure o Spherical nature of gravity makes it round
Neutrinos
o Evidence for fusion in the Sun o Extremely small masses § Travel close to the speed of light o Almost don’t interact with other matter § Requires lead wall 1 light year thick to stop a neutrino o Lots of them: § 1038 neutrinos/sec from the Sun, 1015 coming through you each second o We still can catch some using massive underground detectors
Solar thermostat
o An example of negative feedback o One process happens and then second process happens to reverse the effects of the first process o Slight rise in core temp- leads to large increase in fusion rate- that raises core pressure- causing the core to expand and cool down o Slight drop in core temp- leads to large decrease in fusion rate- that lowers core pressure- causing the core to contract and heat up
Sunspots
o Darker= cooler (still 4,000 K) o Sunspots caused by magnetic fields § Magnetic fields trap gas in huge bubbling loops § Cooler areas at liftoff cause dark sunspots
Flares
o When magnetic field lines in a prominence snap, energy and light are released
Prominences
o If we see the sunspot edge on we can see the loop standing off the surface
Helium Flash
o The event that marks the sudden onset of helium fusion in the previously inert helium core of a low-mass star
Proton-proton fusion cycle
o The chain of reactions by which low-mass stars (including the Sun) fuse hydrogen into helium
Radiation zone in sun
o Gamma ray photons leave the core and move into an area known as the radiation zone § Neutrinos? No interaction because they are gone § Positrons? Quickly find electrons in the core to annihilate with o So dense that photons can’t get very far without running into something o Energy is transported primarily by radiative diffusion
Convection zone in sun
o Eventually gas has cooled (2 million K) § No longer redirects photons, now absorbs them o Main wavelength of photons present: X-rays o Convection: hotter regions rise, cooler regions sink o Energy continues to work its way out (nearly 1 million years total to get to surface)
Open cluster
o A cluster of up to several thousand stars; open clusters are found only in the disks of galaxies and often contain young stars
Globular cluster
o A spherically shaped cluster of up to a million or more stars; are found primarily in the halos of galaxies and contain only very old stars
HR diagram
o A graph plotting individual stars as points, with stellar luminosity on the vertical axis and spectral type (or surface temp) on the horizontal axis
MS turnoff on HR diagram
o The point on a cluster’s HR diagram where its stars turn off from the MS; the age of the cluster is equal to the MS lifetime of stars at the MS turnoff point
E=MC2 (mass energy equivalence
o The potential energy of mass
Wavelength-frequency relation
o Lambda X frequency = c
Gas clouds (dark molecular)
o Clouds that are made mostly of complex molecules such as carbon dioxide and sulfur dioxide o Cool dense, interstellar clouds in which the low temps allow H atoms to pair up into H molecules (H2)
Nebulae
A cloud of gas in space, usually one that is glowing
Protostar
o A forming star that has not yet reached the point where sustained fusion can occur in its core
Main sequence
o Stars whose temp and luminosity place them on the MS of the HR diagram, all releasing energy by fusing H into He in their cores
Red giant/ supergiant (shell burning)
Supergiants have inert He cores and H burning shells
Horizontal branch star
o Helium main sequence o Our star is happily fusing helium to carbon as a horizontal branch star o Outer layers stopped being pushed out, luminosity decreases o Gravitational equilibrium is restored
Electron degeneracy pressure
o Pressure exerted by electron, as in brown dwarfs and white dwarfs o Supports the core of high-mass stars o Degeneracy pressure supports the core for a bit until the mass of iron gets too heavy
Neutron degeneracy pressure
o Degeneracy pressure exerted by neutrons, as in neutron stars o Low-mass stars
Brown dwarf
o An object too small to become an ordinary star because electron degeneracy pressure halts its gravitational collapse before fusion becomes self-sustaining: have less mass than 0.08Msun
Supernova
o The light weight atmosphere impacts on the heavy core and is bounced off in a huge explosion o Plus huge energy release from neutrinos o Exploding remnant of massive star disperses heavy elements through the galaxy o Inside may be a neutron star: a remnant core of pure neutrons
White dwarf supernova
o If enough mass is accreted, electron degeneracy pressure is overcome (limit: 1.4 M sun (known as the Chandrasekhar limit)) o Star then collapses, carbon fusion begins explosively almost everywhere in WD (bye white dwarf) o Occurs in only binary systems and older star systems o Nothing left and every white dwarf supernova looks the same each time
Massive star supernova
o Found in young star formation regions o Makes a neutron star or black hole o Luminosity of about 10 billion suns
Neutron star
o Structure determined by gravity vs. neutron degeneracy pressure o Size: 10 km o Mass: 1 to 3 Msun o Made of degenerate neutrons o Crushing gravity at its surface § Sun’s worth of mass compressed into a city size o Neutrons spinning very rapidly
X-ray binary
binary star system that emits substantial amounts of X-rays, thought to be from an accretion disk around a neutron star or black hole
X-ray burster
o an object that emits a burst of X-rays every few days; each burst lasts a few seconds and is thought to be caused by helium fusion on the surface of an accreting neutron star in a binary system, means its not a black hole
Pulsar
o A neutron star from which we can see rapid pulses of radiation as it rotates
Mass exchange
o (in close binary star systems) the process in which tidal forces cause matter to spill from on star to a companion star in a close binary system
Black hole
o Object’s whose escape velocity is faster than the speed of light o Inside this radius not even light can escape (can fall in but never get out) o We can’t see any light coming from inside § Black hole o NO hard surface § Event horizon is a mathematical point of no return § Matter only exists at the singularity (with infinite density)
Accretion disk
o A rapidly rotating disk of material that gradually falls inward as it orbits a star-like object (white dwarf, neutron star, or black hole)
Equivalence principle
o The fundamental starting point for general relativity which states that the effects of gravity are exactly equivalent to the effects of acceleration
Event horizon (Schwarzschild radius)
o Is the point at which escape velocity equals speed of light
Spiral galaxy
o Disks (with spiral arms) o Spheroids (bulges and halos) o Look like flat white disks with yellowish bulges at their centers o Disks are filled with cool gas and dust, interspersed with hotter ionized gas, and usually display spiral arms
Elliptical galaxy
o All bulge/halo (no disk) o Very few young stars o Very little cool dust/gas o Reddish color= old stars (red giants, red main sequence)
Irregular galaxy
o Galaxies in formation? o Or transition? o Or failed? o Often LOTS of star birth o Look neither spiral or elliptical
Rotation curve (spiral galaxy)
o A graph that plots rotational (or orbital) velocity against distance from the center for any object or set of objects o Nearly all galaxies show similar rotation curves o Flat rotation curves of these galaxies indicates large amounts of matter in the outer regions (dark matter)
Gravitational lensing
o The magnification or distortion (into arcs, rings, or multiple images) of an image caused by light bending through a gravitational field, as predicted by Einstein’s general theory of relativity
Dark energy/dark matter
o More the 90% of the mass of the universe is dark matter (invisible , “missing” matter) o Detectable only via its gravitational force on “luminous” matter (gas and stars) o Name sometimes given to energy that could be causing the expansion of the universe to accelerate o Matter that we infer to exist from its gravitational effects but from which we have not detected any light; apparently dominates the total mass of the universe
Critical universe
o Density of matter= “critical density” o Decelerating universe: will expand forever but just barely o Will never collapse, but expands more and more slowly as time progresses, in the absence of a repulsive force o Average mass density equals the critical density
Coasting universe
o The universe has always expanded at the same rate § Constant expansion § No deceleration due to gravity o Actual mass density is smaller than the critical density
Recollapsing universe
o Dark matter density is greater than critical density o Decelerating universe: § Expansion will stop in the future, then collapse (Gnab Gib, oscillations?) o Collective gravity of all its matter eventually halts and reverses the expansion, causing the galaxies to come crashing back together and the universe to end in a fiery Big Crunch
Accelerating universe
o “Dark energy”: more prevalent than every other form of mass/energy o A force that counteracts gravity? § Truly an unknown force in all of physics o The cosmological constant actually exists (Einstein) o It will become cold and dark more quickly than a coasting universe
Disk
o Portion of a spiral galaxy that looks like a disk and contains an interstellar medium with cool gas and dust; stars of many ages are found in the disk
Bulge
o Central portion of a spiral galaxy that is roughly spherical and bulges above and below the plane of the galactic disk
Halo
o Spherical region surrounding the disk of a spiral galaxy
Sagittarius A
o Source of radio emission o In the center of the galaxy o Several hundred stars crowd the region within about 1 ly of Sgr A o Turbulent region
Clusters of galaxies
o A collection of a few dozen or more galaxies bound together by gravity, smaller collections of galaxies are simply called groups
Local group
o The group of about 40 galaxies to which the Milky Way Galaxy belongs
Hubble's law of recession
o V=hubble’s constant X d o Mathematical expression of the idea that more distant galaxies move away from us faster o V is the galaxy’s speed away from us o D is its distance
Chandrasekhar limit
o White dwarf limit o The maximum possible mass for a white dwarf which is about 1.4 Msun
Standard candles
o An object for which we have some means of knowing its true luminosity, so that we can use its apparent brightness to determine its distance with the luminosity-distance formula
Cepheid variables
o A particularly luminous type of pulsating variable star that follows a period-luminosity relation and hence is very useful for measuring cosmic distances
Cosmological principle
o The idea that matter is distributed uniformly throughout the universe on very large scales, meaning that the universe has neither a center nor an edge
Big Bang Theory
o States that all matter in our observable universe came into being at a single moment in time as an extremely hot, dense mixture of subatomic particles and radiation
Inflation
o A sudden and dramatic expansion of the universe thought to have occurred at the end of the GUT era
Cosmic radiation background
o The remnant radiation from the Big Bang, which we detect using radio telescopes sensitive to microwaves (which are short-wavelength radio waves)
Olber's paradox
o A paradox pointing out that if the universe were infinite in both age and size (with stars found throughout the universe), then the sky would not be dark at night
Hubble constant
o Expresses current rate of expansion of the universe o Reciprocal is the age the universe would have if the expansion rate had never changed
Doppler redshift
o A Doppler shift in which spectral features are shifted to longer wavelengths, observed when an object is moving away from the observer
Gravitational redshift
o A redshift caused by the fact that time runs slowly in gravitational fields
Cosmological redshift
o The redshift we see from distant galaxies, caused by the fact that expansion of the universe stretches all the photons within it to longer, redder wavelengths
About this deck
By: Jamie Anderson
Textbook: Cosmic Perspective, The (5th Edition)
Essential Cosmic Perspective, The (5th Edition)
Created: 2011-04-29
Size: 93 flashcards
Views: 84
Textbook:
Cosmic Perspective, The (5th Edition) Essential Cosmic Perspective, The (5th Edition)Created: 2011-04-29
Size: 93 flashcards
Views: 84
About StudyBlue
STUDYBLUE makes things that make you better at school.
Things like online flashcards with photos and audio.
Things like personalized quizzes and friendly reminders about when (and what) to study next.
Think of it as a digital backpack™: access to all of your study materials online and on your phone.
STUDYBLUE exists to make studying efficient and effective for every student, for free. Join us.
“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy
Kathy